WW-0545 Reviewed 1997
Apricots are fast-growing small trees with a life expectancy of 20 to 30 years. They grow best on a well-drained soil in full sun. Flower buds are often killed during the winter. When this happens there is no fruit or bloom the following year. The attractive white to pink flowers open very early in May and are some times killed by spring frosts. Cool, wet weather inhibits bee pollination activities, often resulting in a small amount of fruit set. Since apricot trees require cross-pollination, plant two or more varieties to ensure fruiting. Fruits make excellent preserves or sauce. Autumn foliage is golden yellow. The apricots listed here are the hardiest available. Trial in zone 4.
Manchurian Apricot (Prunus armeniaca mandshurica), 20 ft. This is the hardiest of the fruiting apricots.
MANDAN APRICOT (Prunus armeniaca mandshurica 'Mandan'), 20 ft., is a vase-shaped tree. Fruits are 1¼ inches in diameter and have a red blush.
MOONGOLD APRICOT (Prunus armeniaca mandshurica 'Moongold'), 15 ft., is a University of Minnesota introduction of 1961. The golden fruits are 1 inch in diameter. Moongold and Sungold apricots are often planted as a pair to ensure fruiting.
SCOUT APRICOT (Prunus armeniaca mandshurica 'Scout'), 15 ft., is a Canadian introduction of 1937. It has 1½-inch fruits.
SUNGOLD APRICOT (Prunus armeniaca mandshurica 'Sungold'), 15 ft., is a University of Minnesota introduction of 1961. Fruits are 1 inch in diameter.
This tree can tolerate soils with a wide range of moisture and fertility. It grows fast and is long-lived. Female trees can produce numerous seeds which can be a nuisance when they germinate in other parts of the landscape. Nurseries often sell grafted male trees to eliminate this problem.
Black Ash (Fraxinus nigra), 40 ft. This native ash grows largely in swamps and wet soils. It has dark green foliage and grows satisfactorily on upland soils. It is the first of the ash to defoliate in the fall. Interest in this species is recent; several selections that hold their leaves longer in the fall have been made in Manitoba and in North Dakota. Zones 3 and 4.
Blue Ash (Fraxinus quadrangulata), 30-40 ft., is a slow-growing ash with a rounded form and glossy, dark green foliage. The twigs are square in cross section with four corky ridges. Trial in zone 4.
Green Ash (Fraxinus pennsylvanica), 50-60 ft., is the most common species of ash planted in shelterbelts, windbreaks, along streets, and on lawns in Minnesota. Although this tree is quite upright when young, it later develops a well-rounded crown. Leaves come out late in the spring and drop soon after the first fall frost. Fall color is yellow. Green ash is very hardy, drought resistant, and alkali tolerant. Male selections are usually planted unless used for shelterbelts and windbreaks. Zones 3 and 4.
KINDRED GREEN ASH (Fraxinus pennsylvanica 'Kindred'), is a fast-growing tree with a straight trunk and good foliage. It is seedless. Zones 3 and 4.
MARSHALL SEEDLESS GREEN ASH (Fraxinus pennsylvanica 'Marshall Seedless') is an ash that recovers quickly after transplanting. It is broad and has good quality foliage. Zones 3 and 4.
SUMMIT GREEN ASH (Fraxinus pennsylvanica 'Summit') is narrower than most seedlings of green ash trees, making it useful for boulevard plantings. At the arboretum, the ash plant bug has been more of a problem on this selection than on other green ash cultivars. Zones 3 and 4.
White Ash (Fraxinus americana), 50-60 ft., is a native tree tolerant of dry soils. It is similar to the green ash, but has a purple fall color. The selections Rosehill and Autumn Purple have not been dependably hardy. Minnesota nurseries are beginning to grow trees started from trees native to the area south of Mille Lacs Lake. These should be hardy in zones 3 and 4.Picture of a Marshall seedless green ash tree Picture of River birch bark
BASSWOOD (See LINDEN)
Beech is a common name applied to two unrelated genera. Both kinds do best on a fertile, moist, well-drained soil. Both are shade tolerant, but grow better with more light.
American Beech (Fagus grandifolia), 65 ft. or more. The American beech tree is quite dense and has a shallow root system. It has good quality dark green foliage that turns yellow in the fall. Bark is smooth and gray. Trial on protected sites in zone 4.
Blue Beech (Carpinus caroliniana), 20 ft. The blue beech is a native small tree or large shrub with smooth, muscle-like stems that are silvery-gray. Leaves turn orange to red in the autumn. Blue beech is an excellent plant for screening or background planting. Zones 3 and 4.
Most species of birch prefer cool, moist sites. When birches are planted in landscapes where conditions are different from their native habitat, they are likely to suffer stress and may become infested by bronze birch borers. These borers can kill birches within a few years after planting. A northern exposure is better for birch than one to the south or west.
Birch trees should be fertilized in the spring, watered through the summer, and mulched with an organic mulch to keep the soil cool beneath the trees. Keeping birches in good condition minimizes birch borer problems.
European Birch (Betula pendula), 30 ft. This white-barked birch is similar to our native paper birch, having the same site requirements, but it is very susceptible to the bronze birch borer. The cultivar Gracilis, commonly called the Cutleaf Weeping European birch is more widely planted than the species. It, too, is very susceptible to borer damage. Zones 3 and 4.
Paper Birch (Betula papyrifera) 30-40 ft., is native throughout the state on moist sites and on cool north slopes. The white, papery bark makes this a popular tree for landscaping. This species is susceptible to the bronze birch borer when planted on hot, dry sites or where the soil is likely to become compacted. Zones 3 and 4.
River Birch (Betula nigra), 40 ft., is a graceful tree with a rounded crown. The loose, papery bark is reddish brown and darkens as the tree becomes older. This tree can be grown with a single stem or as a clump tree. It has been resistant to the bronze birch borer. Although native in river bottoms in the southeast corner of the state, river birch grows well on upland soils. Hardy in zone 4, trial in the southern part of zone 3. It is growing well at the North Central Experiment Station at Grand Rapids.
BLACK LOCUST (see LOCUST)
Box Elder (Acer negundo), 50 ft., is a fast-growing, large, spreading tree. Its compound leaves have three to five leaflets. It is native throughout most of the state and is sometimes planted in shelter belts and windbreaks in western Minnesota. Although this tree is a maple, it is not recommended for lawn or street plantings because of its irregular form and susceptibility to breakage in wind and ice storms. It is tolerant of infertile dry sites. Female plants harbor the annoying boxelder bug. Zones 3 and 4.
Ohio Buckeye, (Aesculus glabra), 50 ft., is a slow-growing, round-headed tree. Flowers are creamy yellow in upright clusters and bloom in early June. Fruits are conspicuous and slightly spiny on the surface. Usually a single, rounded, shiny brown seed is produced in each fruit. These can create a litter problem. Leaves have a good green color in summer and are golden to orange in the fall. This tree is quite free of insect problems, but leaf diseases can cause leaf discoloration and defoliation in late summer. Large trees are difficult to transplant because they grow a deep tap root. Transplanting can be avoided by planting seeds in the fall where the tree is to grow. Zones 3 and 4.
Butternut (Juglans cinerea), 40 ft. A native tree as far north as Aitkin County, the butternut produces a spreading, rounded crown with large, compound leaves that are soft and hairy underneath. The edible nuts are elongated, with a deeply furrowed shell. This tree requires a rich, fertile soil. Unless butternut trees are nursery-grown or moved as seedlings, they are difficult to transplant because of a deep tap root. Hardy in zone 4; trial in the southern part of zone 3.
Catalpa (Catalpa speciosa), 40 ft. This is the largest of the catalpas and the hardiest. The leaves are very large and heart-shaped. The flowers are large and creamy white with yellowish and brown markings. They are attractive on the tree but litter the ground for a short time when they drop. Leaves fall all at one time following a killing frost. The long, narrow, fruiting pods hang on the tree all winter. Avoid dry or exposed sites. Hardy only in the southern part of zone 4. Trees grown in other areas are often disfigured by winter injury.
Cherries are a diverse group that should be grown in full sun on well-drained soils.
Amur Cherry (Prunus maackii), 30 ft. This is a small tree, native to Siberia, planted for its reddish brown, almost metallic-looking bark, which flakes off in papery strips. This tree is especially attractive in winter. Amur cherry is a close relative of our native chokecherry. Zones 3 and 4.
Black Cherry (Prunus serotina), 50 ft. Although native to Minnesota, this tree is not commonly planted. White flowers in long pendant clusters are followed by astringent cherries that are black at maturity. This tree produces a high quality wood used for furniture. Hardy in zone 4; trial in zone 3.
Canada Red Cherry (see Chokecherry).
Chokecherry (Prunus virginiana), 15 ft. This can be grown as a small tree or a large shrub. It has pendant clusters of white flowers that open in late May. Fruits ripen in July and August and turn black at maturity. They are readily taken by birds or can be used for cooking or winemaking. Chokecherries are useful in shelterbelts, windbreaks, and wildlife plantings. The selection called Shubert has green leaves that turn dark maroon several weeks after they emerge. Chokecherries often produce suckers at the base of the plant. These must be removed if the plant is to be maintained as a tree rather than a shrub. Canada red chokecherry is similar to Shubert, but is reported to have a straighter trunk and a better distribution of branches to make a better formed tree. Zones 3 and 4.
European Bird Cherry (Prunus padus), 25 ft. This small tree resembles our native chokecherry but blooms about two weeks earlier. The cultivar Commutata, called the May Day tree, has large flowers and is often in bloom by May 1. This plant is very susceptible to black knot, a fungus disease causing dark enlarged swelling of the branches, marring the beauty of the tree. Zones 3 and 4.
Shubert Chokecherry (see Chokecherry).Picture of a Shubert chokecherry
Kentucky Coffee Tree (Gymnocladus dioica), 50-65 ft., is an open, spreading tree with large, finely divided leaves. Large, broad pods add interest during the winter. Occasionally the quantity of pods can cause a litter problem. The bark is deeply furrowed and the coarse branches have few lateral twigs. It is native in southern Minnesota as far north as the Twin Cities. It is slow to leaf out in the spring; fall color is usually a golden yellow. Hardy in zone 4; trial in zone 3.Picture of a Kentucky coffee tree
Amur Cork Tree (Phellodendron amurense), 45 ft. This is the only cork tree that is available from Minnesota nurseries. It develops an open, spreading crown with coarse branches. The bark is deeply furrowed and corky. Foliage is dark green and free of insect and disease problems. Female trees produce clusters of green, berrylike fruits that turn black at maturity and are readily eaten by birds. Hardy in the southern part of zone 4; trial in the northern part of zone 4.
COTTONWOOD (see POPLAR)
CRABTREE (see FLOWERING CRABTREE)
Because of the widespread Dutch elm disease in the state, planting elms is not recommended at the present time. There are several hybrid elms that are reported to be resistant to this disease. Several are being evaluated in arboretum plantings.
American Elm (Ulmus americana), 60-65 ft. This species was widely planted throughout the Upper Midwest and is still our most common street tree even though many thousands have been lost. The vase-shaped form and arching branches are quite distinctive. The root system is quite shallow and often disrupts sidewalks and curbs. Hardy in all zones.
Red or Slippery Elm (Ulmus rubra), 60-65 ft, is a large tree that is native to river bottoms and lowlands. It is not widely planted. It is susceptible to Dutch elm disease. Hardy in zones 3 and 4.
Rock Elm (Ulmus thomasii), 60-65 ft. This species may be distinguished by corky ridges on the twigs. It has never been widely planted and is susceptible to Dutch elm disease. Zones 3 and 4.
Siberian Elm (Ulmus pumila), 40 ft. This elm is often incorrectly called Chinese elm. It is smaller than our native elm and has smaller leaves. Siberian elms grow quite fast when young. Hardiness varies with the seed source; some strains are not hardy. The Harbin strain is the hardiest. This species is more resistant than native species to Dutch elm disease but is not entirely immune. It is often planted in windbreaks and shelterbelts. Hardy strains are hardy in all zones.
Flowering Crabapples (Malus hybrids and cultivars) are some of the most useful small trees in Minnesota. Crabapples bloom abundantly in the spring and some have an attractive display of fruit for six or more months. Different kinds vary in size from 7 to 25 feet. Foliage colors vary from a light, bright green to deep maroon to silvery red. Forms may be horizontal, columnar, rounded, or weeping. Most flowering crabapples have little or no fall color, but a few do turn a clear yellow. Fruits larger than one inch can cause a litter problem when they drop.
There are two important diseases that can infect flowering crabappleapple scab and fireblight. Apple scab is a fungus disease that causes small sootlike spots on the leaves. If infection becomes severe, leaves yellow and drop. Trees that are susceptible to this disease sometimes lose their leaves in late July or early August. Scab does not kill the plant.
Fireblight is a bacterial disease that can cause severe injury or death to flowering crabapples. Infected branches turn black during the growing season. Diseased trees seem to be more susceptible to winter injury. Different species and cultivars vary in their susceptibility to fireblight. Chemical control is normally not practical, and so less susceptible selections should be planted.
Flowering crabapples are intolerant of poorly drained soil and are best planted on a soil of medium fertility. They should be grown in full sun. Shade will diminish the quantity of bloom and fruit.
Trees growing in grassy areas should be protected in the fall from rodent damage which may occur during fall and winter. Hardiness varies within the species and among cultivars. Most, but not all, flowering crabapples are hardy. Unless indicated otherwise, all those listed here are hardy in zones 3 and 4.
Almey Flowering Crabapple, 15 ft., has an irregular form and branching habit, with deep, rose-red flowers. It often loses its leaves in late July or August because of disease.
David Flowering Crabapple, 10-15 ft. An abundance of pure white flowers is followed by ½-inch fruits that turn bright red and remain on the tree until March or April, providing winter interest. Most winters David crabapples have been fully hardy, but winter injury has been known to occur. Trial in zones 3 and 4.
Dolgo Flowering Crabapple, 25 ft. This tree, which has light red flowers with a light colored center, is not normally considered an ornamental but is grown for the bright red, ¾-inch fruits which are used for jelly.
Flame Flowering Crabapple, 15 ft., was introduced by the University of Minnesota in 1934. It has white flowers and bright red fruits, ¾ inch in diameter. It is susceptible to scab, but usually the disease does not defoliate the tree.Picture of a Flame flowering crabapple
Hopa Flowering Crabapple, 25 ft., has reddish flowers and red-green leaves. It is susceptible to scab, which often causes midsummer defoliation. The oblong, 1 inch fruits are bright red and are often used for jelly. Fruits drop at maturity.
Kelsey Flowering Crabapple, 20 ft., is a Canadian introduction with deep rose-red double flowers. Spring foliage is dark red, turning to red-green. It has little or no fruit.
Pink Spires Flowering Crabapple, 15 ft., has an upright form with red-tinged leaves. Flowers are light rosy-lavender. Fruits, which measure ½ inch, are deep purple-red.
Radiant Flowering Crabapple, 15 ft., was introduced by the University of Minnesota in 1958. It has a rounded shape. Rosy-red flowers are followed by fruits, ¾ inch in diameter, that turn deep red when ripe. Apple scab can cause some premature defoliation.
Red Jade Flowering Crabapple, 10-15 ft. This is a weeping white-flowered tree with attractive medium green leaves. The bright red fruits measure ½ inch and remain on the tree into the winter. Red jade is susceptible to fireblight, which can cause slight branch injury or severe dieback.
Red Silver Flowering Crabapple, 15-25 ft., has red flowers followed by ¾-inch fruits that are deep maroon in color. Foliage is purple-red.
Red Splendor Flowering Crabapple, 25 ft. Somewhat vase-shaped when young, this tree spreads out with age. Flowers are light rose-red. Fruits, ½ inch in diameter, are showy from late July until March or April, but may be taken by birds. Seedlings of red splendor are being sold for windbreak and shelterbelt plantings, but if they are called red splendor, they are misnamed. To be called red splendor, the plants must be grafted, not seedlings. Seedlings will vary in flower color, fruit size, and in length of time that the fruits persist.
Royalty Flowering Crabapple, 20 ft., has deep crimson flowers, with deep red leaves that provide little contrast with the flowers. Leaves remain attractive through the entire season. If this selection becomes infected with fireblight, injury can be severe.
Snowdrift Flowering Crabapple, 20-25 ft. This tree has pink buds that are white when open. Foliage is a medium green. The abundant ½-inch fruits are red. This tree has a broad oval form. Some plants have shown some fireblight injury while others have not been infected.
Sparkler Flowering Crabapple, 15 ft. Introduced by the University of Minnesota in 1969, this tree starts blooming at a very young age and blooms heavily each year thereafter. Only a few ½-inch dark fruits are produced, but they persist into the winter. This tree has a broad, horizontal form.
Spring Snow Flowering Crab, 20-25 ft. This is an upright tree with white flowers, but usually without fruit. Most years it has been free of fireblight, although one year some plants at the arboretum were apparently damaged by this disease.
Ginkgo (Ginkgo biloba), 50 ft. The ginkgo is a tree of prehistoric origin that has an interesting fan-shaped leaf with parallel veins. During the summer the leaves are green. During a mild, long fall leaves will turn yellow; otherwise they often freeze on the tree and drop all at once. Leaves are usually not injured by insects, disease, or air pollution. Since female trees produce fruits that are ill-smelling when they decay, trees sold by nurseries often are grafted male trees. Seedling ginkgoes are not winter hardy in Minnesota. Once trees reach a height of 3-4 feet they survive the winters in the southern part of zone 4 without injury. For that reason it is advisable to plant one that is at least 4-5 feet tall.
Ginkgoes transplanted with a ball of soil seem to become established more quickly than those moved bare root. Trees planted bare root grow very slowly for two to three years. The growth rate of established trees in the arboretum has been about one foot annually.Picture of Ginkgo foliage
Hackberry (Celtis occidentalis), 50-60 ft. This tree has a form similar to that of elm. It will grow on many sites but grows fastest on fertile, moist soils. The deep root system makes hackberry quite drought tolerant. It often takes two years to reestablish itself after transplanting. Several problems are common to this tree. One is an insect gall that causes a wartlike growth on the leaves. However, these do not significantly affect tree growth. Clusters of twiggy outgrowths on some branches, called "witches broom," are common on hackberry, but cause no apparent damage.
Hackberry has small green berries that turn purplish at maturity. The medium-green summer foliage may turn yellow in the fall if severe weather is delayed. The bark is rough with prominent, short, corky ridges. This is a useful tree for shade, windbreaks, shelterbelts, and street plantings. Adapted to zone 4; trial in zone 3.
Hawthorns or thornapples are small trees commonly used for landscape planting. Minnesota has many native species and numerous natural hybrids. Identification is often difficult. Most of the native plants, as well as those brought in from other areas, are susceptible to cedar-hawthorn rust, which causes yellow spotting of the foliage. Some hawthorns become so badly infected that their leaves are more yellow than green. Severe infection may cause browning of the foliage and premature defoliation.
Hawthorns are trees that are adapted to well-drained soils and full sunlight. Most produce an abundance of long, sharp thorns, but selections without thorns can be planted where thorns might cause problems. Most trees produce white flowers that have an unpleasant fragrance. Most produce fruit that are ½ inch in diameter and which turn red at maturity. Some drop their fruit in late summer while others retain their fruit until spring.
Hawthorns are most commonly found in the southern half of the state, but some are native in northern areas. Other species and selections of hawthorns vary in hardiness and may not be adapted to Minnesota conditions.
Many native hawthorn trees have a horizontal growth habit, with an almost Oriental appearance. Despite the rust problem of the native hawthorns, they are an asset to the landscape.
Cockspur Hawthorn (Crataegus crus-galli), 10-15 ft. This tree has glossy, bright green leaves that are nearly resistant to cedar-hawthorn rust. Trees produce white flowers followed by fruits that are dark red at maturity. The fruits are retained on the trees until spring unless taken by birds. Flowering sometimes does not occur until several years after planting. Trees have a horizontal habit. Thorns are about two inches long. A thornless form of this hawthorn is available at nurseries. Adapted to zone 4 and the southern half of zone 3; trial in the northern half of zone 3.
THORNLESS COCKSPUR HAWTHORN (Crataegus crus-galli inermis), 10-15 ft., is similar to cockspur hawthorn, but without thorns. Hardiness zones are the same as for cockspur hawthorn.
English Hawthorn (Crataegus laevigata), 15 ft., has lacked hardiness and has frequently has tip dieback due to winter injury. Branch dieback has occurred several winters on plants in the arboretum. Zone 4.
PAUL'S SCARLET HAWTHORNE (Crataegus laevigata 'Paul's Scarlet'), 15 ft., (see English Hawthorn).
Toba Hawthorn (Crataegus x mordenensis 'Toba'), 10-16 ft. This hawthorn is susceptible to hawthorn-cedar rust, which discolors the leaves but does not cause defoliation. The long-lasting double flowers open white and turn pink as they age. The bright red ½-inch fruits drop in September. For unexplained reasons the trunk is somewhat twisted. This tree is somewhat short-lived and may last only 10 to 15 years. Hardy in Zone 4; trial in zone 3.
Washington Hawthorn (Crataegus phaenopyrum), 30 ft., has lacked hardiness in arboretum trials. Zone 4.
Hickories are not commonly planted because their deep tap roots make transplanting difficult. All do best in rich, fertile, moist soil with good drainage. Seed should be planted in the fall where the trees are to grow, eliminating the need to transplant, or they can be stored over the winter in moist sand or peat and planted in the spring.
Bitternut Hickory (Carya cordiformis), 40-50 ft. This tree is native as far north as Mille Lacs Lake. It has a nonedible nut and a smooth, gray bark. Adapted to zone 4; trial in zone 3.
Shagbark Hickory (Carya ovata), 50-80 ft. Native in southeastern Minnesota, this tree has a bark that becomes shaggy with age, separating in long narrow strips. The nut has a delicate flavor, but it is difficult to crack. Hardy in the southern part of zone 4.
Honey locusts (Gleditsia triacanthos inermis and cultivars) are fast-growing members of the pea family. They are tolerant of dry sites. They leaf out late in the spring. The foliage allows some light to penetrate the crown, making it possible to grow a lawn beneath the tree, yet it is dense enough to provide a pleasant shade. Leaflets are tiny and so, when they drop in the fall, little raking is required.
Honey locusts sold in nurseries are usually grafted thornless selections that do not produce seed pods, although occasionally they will produce a few pods. Seedlings can produce an abundance of long, flat seed pods, which creates a litter problem. Flowers are inconspicuous and green. Seedling honey locusts sometimes have branch thorns that are 6 inches or more in length.
Some honey locusts have an arching main trunk, which may not be objectionable in some landscapes. But if a large shade tree is needed, select a honey locust with a strong upright central trunk or be prepared to do some corrective pruning. Prune during periods of low humidity during the growing season.
Recently, some honey locusts in Minnesota have become infected by a fungus disease that can badly disfigure or kill these trees. Infection often occurs at the base of branches and encircles the trunk. Presently there is no chemical control. Pruning during dry periods helps minimize the chance of spreading the disease.
Honey locusts are intolerant of wet soils, and should receive full or nearly full sunlight. They are best adapted to the southern parts of zone 4 northward to the Twin Cities. When planted further north, many die back to the ground because of winter injury. There are scattered honey locusts in the northern areas of the state to Moorhead, and near Lake Superior in Duluth.
Thornless Honey Locust (Gleditsia triacanthos inermis), 50-60 ft., is reproduced from seed rather than from grafts, and so some trees will produce numerous seed pods. Size and shape of each will vary.
IMPERIAL HONEY LOCUST (Gleditsia triacanthos inermis 'Imperial'), 30-40 ft. This selection is more spreading than upright and often lacks a single central trunk. Foliage is dark green. Because the leaflet spacing is closer than most and branches are more closely spaced, this selection is denser than most honey locusts.
MAJESTIC HONEY LOCUST (Gleditsia triacanthos inermis 'Majestic'), 40-50 ft., is nearly as broad as it is tall.
RUBY LACE HONEY LOCUST (Gleditsia triacanthos inermis 'Ruby Lace'), 15 ft., is not as commonly available as in past years. It is often injured during the winter in the Twin Cities area, sometimes killed to the base. The maroon spring foliage is attractive, but turns an unattractive brown in the summer. It usually has poor tree form.
SHADEMASTER HONEY LOCUST (Gleditsia triacanthos inermis 'Shademaster'), 50-60 ft., is a selection that has a strong central trunk and ascending branches.
SKYLINE HONEY LOCUST (Gleditsia triacanthos inermis 'Skyline'), 50-60 ft. This selection develops a stronger trunk than many, giving the tree a slightly pyramidal form.
SUNBURST HONEY LOCUST (Gleditsia triacanthos inermis 'Sunburst'), 30-40 ft. New growth is a bright yellow, and so in the spring the entire tree is yellow. As the foliage ages it turns green, but the tips of the growing branches are yellow. This selection is very fast-growing, but occasionally the wind causes some branch breakage. It is slightly less hardy than the other honey locusts, with occasional winter injury occurring in the Twin Cities area.Picture of a Honey locust
HOP HORNBEAM (see IRONWOOD)
Horse Chestnut (Aesculus hippocastanum), 40-50 ft. The horse chestnut is often confused with the Ohio buckeye, but the buckeye is much hardier and therefore more common. The winter buds of the horse chestnut are large and sticky, whereas the buckeye's are small, dark brown, and dry. Horse chestnut has a long tap root making it difficult to transplant in larger sizes. Large upright clusters of cream-colored flowers appear in June and are followed by large nonedible nuts. The foliage often becomes blemished with various leaf spot diseases and marginal drying. This tree can provide dense shade. It is suggested for trial in protected locations in the southern half of zone 4.
Ironwood or Hop Hornbeam (Ostrya virginiana), 25-40 ft. This is a common native, occurring over much of the state, often growing beneath other trees. Although shade tolerant, the ironwood will grow better in full sun. It is quite free of insect and disease problems and will tolerate a wide range of soils, except poorly drained soils. It can be grown as a clump or as a single-trunk tree. Fall color is yellow to brown. Some leaves persist into winter, providing winter interest. Seeds are born in interesting hipline pods at the tips of branches. Zones 3 and 4.Picture of an Ironwood
Tree Lilac (Syringa reticulata), 20-25 ft. Has a dark cherrylike bark. The tree has an interesting irregular form, but it can be pruned to have a straighter trunk. Tree lilacs can be grown as clump trees. Tree lilacs bear large clusters of cream-colored flowers in late June. To some the flowers are fragrant, but to others they have an odor that is unpleasant at close range but that is not objectionable in the landscape. Tree lilacs tend to bloom heavily every other year. Brown seed clusters, irregular growth habit, and texture and color of bark add winter interest. Zones 3 and 4.
KENTUCKY COFFEE TREE (see COFFEE TREE)
The American basswood is native to Minnesota and is available from nurseries, but the European linden is sold more often. These trees do best on a rich moist soil, but tolerate a wide range of soils. Although tolerant of shade, they grow better in full sunlight. Trees grown in forests tend to be somewhat narrow and leggy, but when grown in the open, they develop full, rounded crowns. They are quite free of insect and disease problems.
American Linden or Basswood (Tilia americana), 50-80 ft., has small clusters of fragrant cream-colored flowers in late June. Fall color is yellow to brown. American linden makes a good single-trunk tree as well as a clump tree. Some plants tend to produce many watersprouts at the base of the trunk, which can be removed by pruning. This native species is adapted to both zones 3 and 4.Picture of an American linden
Greenspire Linden (See Little Leaf Linden).
Little Leaf Linden (Tilia cordata), 50 ft., is similar to the American linden, but it has smaller leaves and finer branches. It is also slower-growing. Little leaf linden tend to be somewhat pyramidal in form. Adapted to southern parts of zone 4. In the Twin Cities area, trees that are fertilized and watered late in the summer can be subject to winter injury.Picture of a Greenspire linden Picture of a different Greenspire linden
GREENSPIRE LINDEN (Tilia cordata 'Greenspire'), 50 ft. This is a selection of little leaf linden with a strong central trunk, which gives the tree a broad pyramidal form. Adapted to the southern part of zone 4.
Redmond Linden (Tilia x euchlora 'Redmond'), 40-50 ft. The leaves of this linden are larger and darker green than those of little leaf linden. The tree is dense with a pyramidal form. It apparently reestablishes itself more quickly after transplanting if moved with a ball of soil rather than if moved bare root. Adapted to the southern part of zone 4.
This common name is used for both honey locust and black locust trees, both members of the legume family. Black locust has showy flowers, whereas the honey locust has inconspicuous ones. Black locusts have pairs of short thorns, whereas honey locusts either are thornless or have long thorns that are sometimes branched. For information on honey locusts, see the description under Honey Locust.
Black Locust (Robinia pseudoacacia), 50 ft. In early June this tree produces long clusters of large pealike flowers that are fragrant and cream-colored. Black locust is fast-growing and will tolerate drought. Although there are some large black locusts in the southern half of the state, most have never become large because of injury caused by the locust borer. The borers weaken the trunk, and the trees are blown over. The root system often produces suckers that come up in many areas of the lawn and become a nuisance. Zones 3 and 4.
GLOBE LOCUST (Robinia pseudoacacia 'Globosa'), 10-15 ft., is a dense-growing selection grafted on a standard trunk, providing a globe of dark green foliage on a straight trunk. It is subject to borers that attack the common black locust. Zones 3 and 4.
Magnolias are commonly used in areas with milder climates. Unfortunately, most are not hardy enough in Minnesota and few are available in local nurseries. Even though some are able to survive Minnesota winters, their flower buds are killed during the winter. They will grow best on fertile, moist soil with good drainage in a protected location. Magnolias should be moved with a ball of soil when they are transplanted.
Cucumber Tree Magnolia (Magnolia acuminata), 40 ft., is an upright round-topped tree. Large, inconspicuous greenish yellow flowers appear in late May or early June. This species is one of the hardiest of the magnolias. Hardy in the southern part of zone 4 and on protected sites in the northern part of zone 4.
Merrill Magnolia (Magnolia loebneri 'Merrill'), 15 ft. This small tree has large white flowers with 8 to 15 petals that open in early May. Fruits are cucumberlike pods that expose red seeds when they are mature. Foliage is dark green. Trial in zone 4.
Saucer Magnolia (Magnolia x soulangiana), 15 ft. The large flowers on this tree range in color from white to maroon. Flower bud injury to this magnolia is severe and dieback of the plant is common on exposed sites. It is not dependably hardy for Minnesota except for protected in-town sites in the southern part of zone 4. Some saucer magnolias in the Twin Cities area bloom regularly.
Star Magnolia (Magnolia stellata), 10-16 ft., is often more shrublike than treelike in Minnesota. It is probably the hardiest of the magnolias with showy flowers. Occasionally some of the flower buds are injured, but there are normally enough left to make a good show of white blossoms. In the Twin Cities area the tree normally blooms during the first week of May. Trial in zone 4.
Umbrella Magnolia (Magnolia tripetala), 20-25 ft., has large leaves and flowers. This magnolia does not bloom until the tree is in leaf, so the white flowers, though large, are inconspicuous when they open in June. Plant in an area with wind protection. Trial in zone 4.
Maples are common in both native and planted landscapes in Minnesota. They are a diverse group, ranging in size from shrubs to large trees. Different kinds occur on different sites, and some have quite specific site requirements. All are tolerant of some shade, but most will grow better in full sunlight. Maples are one of the most colorful groups of trees, with fall color dependent on the species, the cultivar, or possibly the site.
Some maples, such as box elder and silver maple, are prolific seed bearers and the seedlings can be a nuisance. The growth rate of maples following transplanting ranges from slow to fast, depending on the species. Most young maples are susceptible to late winter sunscald injury on the trunk. To protect them from the sun, the trunks of young maples should be wrapped each fall until their bark becomes thick and corky.
Amur Maple (Acer ginnala), 20-25 ft. Most often grown as a shrub, the Amur maple makes a desirable small tree if pruned to tree form. It grows fast and can tolerate most soil conditions except wet sites. Fall color varies from plant to plant but is usually very good, often in shades of red, with some trees turning yellow or orange. Amur maple is tolerant of partial shade. Zones 3 and 4.
Norway Maple (Acer platanoides), 50 ft., is a spreading tree that provides dense shade. It grows best on fertile soil. Norway maples normally do not change color in the fall unless the season is long, in which case some will turn a clear yellow. This species and its cultivars are very sensitive to sunscald, and young trees must be wrapped in the fall to prevent sunscald injury to the trunk. They are adapted to southern parts of zone 4 north to the Twin Cities area, although on rare occasions winter injury occurs in the northern part of the zone.
CLEVELAND NORWAY MAPLE (Acer platanoides 'Cleveland') is a fast-growing dense selection with an oval form.Picture of a Cleveland Norway maple
COLUMNAR NORWAY MAPLE (Acer platanoides 'Columnare') is a narrow, upright tree.
CRIMSON KING NORWAY MAPLE (Acer platanoides 'Crimson King') has maroon-red foliage through the growing season. It is sometimes difficult to establish after transplanting, especially on windy sites.
EMERALD QUEEN NORWAY MAPLE (Acer platanoides 'Emerald Queen') has dark green, leathery foliage.
GLOBE NORWAY MAPLE (Acer platanoides 'Globosum') is a globe-shaped tree.
JADE GLEN NORWAY MAPLE (Acer platanoides 'Jade Glen') is one of the fastest growing Norway maples with a good straight trunk.
ROYAL RED NORWAY MAPLE (Acer platanoides 'Royal Red') is reported to be an improvement over Crimson King, easier to transplant and with a brighter color.
SCHWEDLER NORWAY MAPLE (Acer platanoides 'Schwedleri') is a broad tree that has reddish bronze foliage in the spring, which turns a dark green as the leaves mature.
VARIEGATED NORWAY MAPLE or HARLEQUIN NORWAY MAPLE (Acer platanoides 'Variegatum') has leaves with white variegation. This tree needs protection from wind. Sections of the tree that produce green leaves should be removed. Harlequin maple grows very slowly and is more of a novelty tree than a shade tree.
Red Maple (Acer rubrum), 50 ft., is a symmetrical tree native to the slightly acid soils of northeastern Minnesota southward to the central part of the state. This species has small red flowers in mid-April. Fall foliage is usually red, but can also be yellow or orange. Since this maple is native as far south as Florida, only northern strains started from northern seed sources should be planted. A number of cultivars have been introduced but most of these were selected in the East and have not always colored well in this area. Selections made on the West Coast have not been hardy here. Red maples will not grow on alkaline soils. Northern strains are adapted to zones 3 and 4 where soil conditions are suitable.
Silver Maple (Acer saccharinum), 80 ft., is a very large, fast-growing species that is widely planted for shade and wind protection. This species is not recommended for small yards or areas close to buildings because of its size and its brittle wood that breaks in ice and windstorms. Some trees produce a heavy crop of seed that can create litter problems. Seedlings can become a nuisance. Silver maple has a shallow, competitive root system. This tree is sometimes used temporarily in shelterbelts or windbreaks until other species reach a suitable size. Several cut-leaf selections are sometimes planted. Beebe and Weiri are selections that have finely cut leaves. Hardy in all zones.Picture of Silver maple foliage
Sugar Maple (Acer saccharum), 60 ft., is a large, round-headed native tree found in rich, moist soil throughout the wooded portions of the state where broadleaf trees occur. This is one of the most handsome maples, with bright green leaves that turn yellow to orange or scarlet in the fall. It is widely planted for ornamental and street plantings. Sugar maples require a moist, rich, deep soil. Sunscald can be a problem on young trees. It grows slowly when first transplanted, growing at a moderate rate after it is established. The dense crown and relatively shallow roots can create some problems in lawn and garden areas. There are cultivars with distinct forms but they are not commonly for sale in Minnesota. Zones 3 and 4.Picture of Sugar maple foliage
Tatarian Maple (Acer tatarica), 20 ft., is similar to Amur maple and apparently hybridizes with it. Like the Amur maple, it can be grown either as a small tree or a large shrub. Leaves are not as prominently lobed as on the Amur maple. Tatarian maples require an acid soil and are tolerant of infertile soil and partial shade. Autumn color is usually yellow. Zones 3 and 4.
Mountain ash is fast growing, but can be short-lived for several reasons. Sunscald on the trunk during the winter often can cause severe crippling. The trunks of young trees should be wrapped in the fall of each year to prevent such injury. Rings of small holes made by sapsuckers can do severe damage. Within the past decade fireblight, a bacterial disease, has damaged and killed many mountain ash trees in Minnesota. Apparently all species and cultivars are susceptible to this disease. Despite these problems many people are fond of this fast-growing, colorful tree.
In June, mountain ash trees have clusters of cream-colored flowers. In late summer most mountain ashes have pendant clusters of orange to scarlet fruits. These provide bird food from fall into the winter.
American Mountain Ash (Sorbus americana), 20 ft., is native to the cool, moist woods of northern Minnesota. It can be grown as a multistemmed shrub or as a small tree. Small, white flowers appear in dense, flat-topped clusters in June. Bright red, berrylike fruits, about 2 inches in diameter, form in late summer and fall. Birds, especially robins, are fond of the fruits and usually strip the tree of fruits in the fall. Zones 3 and 4.
European Mountain Ash (Sorbus aucuparia), 30 ft. This is the most commonly planted mountain ash. The flowers and fruits are larger than those of the American mountain ash and the orange fruits stay on the tree well into winter. Apparently freezing and thawing are required to soften the fruits to make them palatable to birds. Zones 3 and 4.
Korean Mountain Ash (Sorbus alnifolia), 30 ft., has a dense crown. Unlike most species of mountain ash, it has simple leaves that resemble those of alder. The bark is quite smooth and gray, with prominent white, diamond-shaped markings. Showy white flowers are produced in flat-topped clusters in late May or early June. The small fruits are orange to red and showy in late fall. This species is new to the nursery trade in Minnesota. Hardy in zone 4; trial in the southern part of zone 3.
Showy Mountain Ash (Sorbus decora), 30 ft. This species is native to the north shore of Lake Superior. It is similar to the American mountain ash except that the tree and the fruits are larger. The fruits are usually eaten by birds as fast as they ripen. Zones 3 and 4.
Mulberries are uncommon trees in Minnesota. If one is present, there are likely to be others nearby that grew from seed scattered by birds.
Red Mulberry (Morus rubra), 30 ft., is reported to be native in Minnesota but it is rare. Trial in the southern part of zone 4.
Tatarian Mulberry (Morus alba 'Tatarica'), 20 ft., is often a spreading tree with many dead twigs due to winter injury. The trunk is a yellowish brown. The abundant fruits have a purplish color. This tree is easily identified by its irregularly lobed leaves. Trial in the southern part of zone 4.
Oaks are prominent trees in many natural Minnesota landscapes. Very few oaks are planted because of difficulties in transplanting. Most species have long tap roots, often longer than the height of the seedling tree. Because of this problem, few oaks are sold by Minnesota nurseries at the present time.
Since oak seedlings are fast-growing, they can be started from seed that is planted where the trees are to grow. The acorns should be either planted in the fall or stored during the winter in moist sand in a cool place for planting in the spring. Keeping down competition from weeds will assist survival of the seedlings and increase the growth rate.
Oak wilt, a fungus disease, can kill mature oak trees. Red oaks (with sharp, pointed leaf lobes) are more susceptible than white oaks (with rounded lobes). Oak wilt often enters trees through wounds caused by pruning or by root damage occurring during construction. Once the disease is in a tree it can be spread from tree to tree by root grafts. Wide spacing in landscape plantings should prevent the spread of oak wilt by root grafts. Pruning of oaks should be limited to the dormant season between November and February. The roots of oak trees are very sensitive to changes in soil level. The addition of fill should be avoided because even a small change in soil level can kill the roots. Often such trees die slowly over a period of several years.
Bur oak (Quercus macrocarpa), 30-65 ft. is a picturesque, burly, native tree that will tolerate poor sites. Because of insect problems and the lack of fall color, this species is not often planted. Zones 3 and 4.
Pin Oak (Quercus palustris), 40-60 ft., is sometimes confused with a species common to northern Minnesota, the northern pin oak (Quercus ellipsoidalis). The pin oak has a well-defined central trunk, and the tree has a pyramidal form similar to that of a spruce. Planting on acid soil will avoid iron chlorosis problems. These problems usually occur after 10 to 15 years on pin oaks that are planted on alkaline soils. Fall color is a bright red. Hardy in the southern half of zone 4.
Red Oak (Quercus rubra), 65-80 ft., is a majestic oak with dark green leaves that turn red in the fall. This is one native species that is offered for sale by some Minnesota nurseries. Zones 3 and 4.
Swamp White Oak (Quercus bicolor), 35-65 ft., is a native oak occasionally found in southern Minnesota north to the Twin Cities area. It has a compact root system that lends itself to transplanting. Glossy dark green leaves turn brown in the fall. Zone 4.
White Oak (Quercus alba), 50-65 ft., has a rounded top. It grows best in a fertile, heavy soil. The leaves are green with a whitish underside; they turn red to red-maroon in fall. Some brown leaves persist on the tree into winter. Zone 4 and the southern half of zone 3.
OHIO BUCKEYE (see BUCKEYE)
Wild Plum (Prunus americana), 20 ft., is a native tree that forms thickets throughout the state. White flowers, produced in early May, are showy and fragrant. Fruits are used for jellies and preserves. This species is often planted in windbreaks, shelterbelts, and wildlife plantings. Wild plum roots provide the stock for grafting most of Minnesota's cultivated plums. Suckers are often produced. Unless suckers are removed, a thicket of wild plums will develop. Zones 3 and 4.
Poplars are common in both planted and native landscapes. Some are often planted because of their rapid rate of growth and their adaptability to a wide range of growing conditions.
Some species grow several feet a year but they usually have many problems. A major difficulty is that they are often short-lived because of fungus cankers on the trunk. Many have a shallow, competitive root system that makes it difficult to garden or grow a lawn near them. Some produce seeds in cottonlike masses that are a nuisance. Some species have wood that becomes brittle with age. A few have roots that produce unwanted suckers that come up in lawns or gardens.
Poplars have flattened leaf stems that cause the leaves to rustle in the slightest breeze. Many turn a clear yellow in the fall.
Bolleana Poplar (see White Poplar).
Cottonwood (Populus deltoides), 100 ft., is the largest tree that can be grown in Minnesota. Some cottonwoods have trunks that can be 3 feet in diameter. Because of their immense size they are too big for many landscape plantings. The cottonwood is native along stream banks and in deciduous woods and has been widely planted in western Minnesota shelterbelts. Leaves are triangular, turning a golden yellow in the fall. The 'cotton' from female trees is objectionable when trees are planted near residences. This problem can be avoided by planting male trees. Siouxland is a male selection that is resistant to rust, a disease common to the species, but it is susceptible to canker. Zones 3 and 4.
Japanese Poplar (Populus maximowiczii), 40 ft., has attractive light green bark. In the arboretum it has been fully hardy and shows promise where a fast-growing tree is desired. This species has had some canker. Hardy in zone 4; trial in zone 3.
Lombardy Poplar (Populus nigra 'Italica'), 40 ft., is a tall, upright tree with dark bark and dark, shiny green leaves. These trees are fast-growing but often die within several years or become unsightly because of partial dieback. They are often planted for a screen. Hardy in zone 4; trial in the southern part of zone 3.
Robusta Poplar (Populus x robusta), 40-70 ft., is a fast-growing hybrid poplar that is seedless. It has a broad oval form. It is often used in shelterbelts as a temporary tree until evergreens reach an effective size. They quite often die from canker disease before they reach 15 to 20 years of age. Zones 3 and 4.
Trembling Aspen (Populus tremuloides), 40 ft., is a native tree of interest because of its greenish white bark and its quivering leaves. Suckers come up around the tree so it is best to plant this species where a naturalistic, wooded setting is desired. Leaves turn a clear yellow in the fall. Hardy in all zones.
White Poplar (Populus alba), 40 ft., is a large, broad tree with grayish white bark. Leaves are covered with silvery-white hair on the underside. They are lobed like those of maples and the tree is often incorrectly called "silver maple." This tree has a shallow root system that often sends up suckers that are a nuisance. Zones 3 and 4.
BOLLEANA POPLAR (Populus alba 'Bolleana'), 40 ft., is an upright selection of white poplar that is short-lived because of fungus cankers, but survives longer than the Lombardy poplar. Zones 3 and 4.
Eastern Redbud (Cercis canadensis), 15 ft., is a spreading tree native to areas of the United States south and east of Minnesota. Leaves are large and heart-shaped, turning yellow in the fall. Flowers are rosy pink, opening before the leaves appear. Redbud is variable in hardiness, depending on the strain. Although there are a few large specimens in the Twin Cities and southward, the future for this species in Minnesota depends on the development of hardy selections. At present it is recommended for trial only in protected locations in the southern part of zone 4.
Russian Olive (Elaeagnus angustifolia), 25 ft., is a large shrub or small tree with narrow, silvery-green leaves. It is not an olive, but has an olivelike appearance. Flowers are small, yellow, and very fragrant in mid-June. The silvery fruits are small and plumlike. Russian olive is hardy, drought resistant, and alkali tolerant, but is intolerant of poorly drained soils. It is often planted as a lawn specimen or in background plantings, windbreaks, and shelterbelts. The silvery foliage offers a pleasing contrast with other foliage. Zones 3 and 4.Picture of a Russian olive
THORNAPPLE (see Hawthorn)
Black Walnut (Juglans nigra), 60 ft., is a large tree with wide-spreading branches. It has dark green, compound leaves and edible nuts that are oval, dark brown, and irregularly grooved. Black walnuts are native in southeastern Minnesota and are commonly planted in shelterbelts and as shade trees on large lawns. The dark lumber is used for quality furniture.
Walnut leaves and roots contain a growth inhibitor that adversely affects tomatoes, potatoes, eggplants, and peppers; therefore, walnuts should not be planted near vegetable gardens. This tree grows best on fertile, moist sites. Because walnuts have long tap roots, usually only smaller sizes are transplanted. They are best adapted to the southeastern and southern parts of zone 4, but are grown to a limited extent in other parts of this zone. A few are growing in the southern part of zone 3 where soils are favorable.Picture of a Black walnuts
Willows are common native trees and shrubs. Several species are used in landscape plantings. This group is adapted to a wide range in soil moisture and fertility. Willows become established shortly after transplanting and grow rapidly. The wood of willow trees is brittle, making them susceptible to wind damage.
Corkscrew Willow (Salix matsudana 'Tortuosa'), 20-25 ft., is a novelty tree because of the spiral twisting of its branches. Often older trees are killed by the winter or parts of the tree will winterkill. Younger plants appear to be less susceptible to winter injury. For this reason it is a good practice to start new plants periodically. This tree roots easily from cuttings. Flower arrangers find the branches useful. For protected sites in the southern part of zone 4.
Laurel-leaved Willow (Salix pentandra), 30-40 ft. This is grown as a large shrub or a small tree. The finely toothed leaves are a glossy, dark green. This tree grows especially well on moist sites. Zone 4.
Weeping Willow (Salix alba tristis), 50 ft., is the willow most often used for landscape planting. The golden branches hang down and often touch the ground. Branches are very brittle and are often broken by the wind, making cleanup of the litter an ongoing task. If planted away from intensively maintained landscaped areas, they can still be attractive and the litter will be out of sight. This form of the weeping willow is distinguished from weeping willows of other species by its bright yellow twig color. Hardy in the southern part of zone 3 and 4, although some winter injury can occur in both zones.
White Willow (Salix alba), 50-65 ft. This tree is often used in shelterbelt plantings. The variety of this species, chermesina, has twigs that are red during the winter. It is often grown as a shrub cut to the ground each year, since the red color is most pronounced on young stems. Zones 3 and 4.
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