Most trees bear their flowers and fruit towards the outer tips of branches or on new growth. But there are a few trees that can sprout flowers and fruit directly from mature trunks and branches. This trait is known as cauliflory (from the Latin words for “stem” + “flower”).
Most cauliflorous trees are native to the tropics. Examples include papaya, breadfruit, and that most vital of plants, cacao (the source of chocolate!) Some fig (Ficus) species also exhibit cauliflory. Despite its name, cauliflower doesn’t really count as cauliflorous since it’s not a woody plant.
Even if you can’t make it to the tropics you can still see at least one cauliflorous species. Eastern redbud (Cercis canadensis) is one of few non-tropical tree species that can bear flowers and fruit (actually small papery seed pods) on its trunk and older branches as well as on newer growth. This small ornamental tree is native to much of the Eastern half of the U.S. Eastern redbud is not native to Minnesota but can be grown successfully through Zone 4 if plants from hardy seed strains are selected.
On Saint Patrick’s Day, symbols of Ireland abound. Guinness is poured into glasses and Irish accents grace conversations while shamrocks, the national symbol of Ireland, abound. It is a day that everybody wants to be a little Irish. However, it isn’t just people who want to claim Irish heritage. The potted flowering shamrocks sold at this time of year are not true Irish clovers (Trifolium dubiens or T. repens), but are species from the genus Oxalis. The genus Oxalis is comprised of approximately 800 species found on every continent, save for Antarctica! Most of the species that are grown either commercially or by hobbyists come from areas that are particularly species-rich for Oxalis, most notably South America and costal region of South Africa. Commonly called wood sorrel, shamrocks, good luck plants, or oxalis, there is a wide range of appearances among the species. Leaves may be green to purple in color, hairy or smooth and even marked with dots or stripes. One or more flowers are borne on stems and can be colored white, pink, red, purple or yellow. With such variety, there are many plants that make attractive plants that grow well in the home!
Both the South American and South African types of oxalis have below-ground storage organs. South African species commonly have bulbs and South American species rhizomes, or thickened stems. Upon receiving the bulbs or rhizomes, pot three to five of them in a four inch clay pot. These pots work best because they will provide good drainage and allow air to reach the roots. For South American species, a general soilless potting mix (typically containing peat, perlite, and vermiculite) works well. However, the South African species prefer a mix with more drainage. A mix that has been recommended for the bulb-types consists of: five parts coarse sand, two parts small pebbles, one part soilless potting mix, and one-half part perlite. In order to keep this mix and smaller bulbs from falling out of the drainage holes, place a layer of wet soilless potting mix at the bottom of the pot.
Once the plants are potted up, they must be “forced” into bloom. The temperature that is best for each oxalis will depend on the species. At the beginning of forcing, it is recommended for many of the species that the temperature is between 55-60°F. This may be done by growing pots in cooler areas such as a windowsill or in a cool basement under artificial lights. As roots begin to grow into the medium and shoots emerges, they may be placed in temperatures in the mid 60’s. An exception to these recommendations is the popular Purple Shamrock (O. regnellii atropurpurea). For this plant, start forcing at a warmer temperature around 70°F, then place in temperatures in the mid 60’s after emergence and until flowering. An area with bright light is ideal for these plants, along with regular feeding with a general, balanced fertilizer. Following these general guidelines will produce the most flowers for your enjoyment!
After the plant flowers, it must begin a process that will lead to dormancy. This will be marked by leaves turning yellow, wilting, and eventually falling off. Though this may seem like cruel and unusual punishment, it is very important to maintain the health of the plant. To induce or accelerate the beginning of dormancy, the best practice is to slow down watering, eventually stopping all together. Another practice that helps is to slowly decrease fertilization levels and frequency. This will also help signal to the plant that the dormant period is approaching. When the leaves have all fallen off, it is time to store the bulbs. They may be kept in the pot they were grown in as long as the medium remains moist, but not soggy. An easier and more compact way to store them is in plastic bags with dampened peat moss. Storage should occur in an area with temperatures in the low 40’s and darkness.
While some may be inspired to dance on Saint Patrick’s Day, oxalis are moving every single day! Some plants exhibit nastic (Greek; nastos, close-pressed) movement regularly in response to the environment. Many people are familiar with the sensitive plant (Mimosa pudica) that folds its leaves up in response to touch, a thigmonastic movement. Many species in the genus Oxalis show nastic movement in both leaves and flowers. In response to the day they will open up and, conversely, in response to the night they will close (photonasty). In addition, some species will open when the temperature is warmer and close as the temperature is cooler in the period of a day (thermonasty). These movements help the plant to conserve water and maximize photosynthesis, which are adaptations to surviving harsher environments.
With Saint Paddy’s Day on the horizon, surprise the leprechauns in your life with a pot full o’ something bloomin’ beautiful!
Ornamental grasses are a perennial favorite of consumers. They provide low maintenance groundcovers and serve as focal points in the landscape. However, consumers lament the fact that warm season grasses do not flower until late summer or early fall. Fortunately, Minnesota consumers have an alternative in a group of plants called sedges if they desire a native, grassy plant with spring and early summer interest. Many sedges (Carex species) flower and set seed in May and June to provide early-season interest in the garden.
Currently, the University of Minnesota is conducting research on native sedges to evaluate their landscape potential. Over 20 native Carex species were planted in August, 2005 in the Ornamental Grass Garden at the University of Minnesota Landscape Arboretum. While the trial is ongoing, five sedges so far show fantastic potential for providing early summer ornamental interest.
In order to properly identify sedges, it is necessary to understand a few terms related to their fruiting structures. Carex fruits, which contain the seeds, are called achenes and they are enclosed in a bladder-like sac called a perigynium (perigynia, plural). In taxonomic keys, the shape of the perigynia is important to differentiate Carex species. Most Carex species have separate male and female flowers. The actual flowers on the five following species are not very showy, but the fruiting structures that contain the achenes and seeds are quite conspicuous and ornamental.
Carex crinita, aka fringed sedge, is recommended because of its beautiful foliage. This ~30-inch tall plant exhibits leaves in a lovely chartreuse color when grown in the sun. Compared to other tall sedges, Carex crinita has distinctively wide leaves of up to half an inch across. When it isn’t blooming, the tidy habit is reminiscent of a daylily. Its fruiting structure is also unusual in that it resembles a droopy caterpillar and the species has been nicknamed “caterpillar sedge”.
Although this species thrives in wet prairies and in wetlands, it appears to flourish in a well-mulched and regularly irrigated garden. At the Arboretum, Carex crinita appeared to require full sun. The plants grown under a lattice were much smaller and lacked the distinctive chartreuse color.
Cattail sedge, a two foot tall native sedge, has double appeal because of its attractive foliage and fruiting structures. The lush foliage appears lime green to yellow in the soils at the Arboretum. Of all the sedge species planted in 2005, Carex typhina stands apart due to its yellow hue in both sun and shade. It is unknown whether this species will display yellow foliage in different soil types and pHs. The 3/8 inch wide leaves appear to their best advantage in partial shade. Despite frequent irrigation, the leaves burn in the open sun. This is not unexpected due to the fact that its native habitat is wet woods and prairies. Therefore, this plant is recommended for shade plantings and possibly for sunny rain gardens.
The fruiting structure is the highlight of this plant. The 1 1/4 inch pistillate spikes are composed of pointed perigynia arranged in a cylindrical spike. As the fruiting structures turn from green to brown, the plant starts to resemble miniature cattails. The long lasting fruit persist from June through October. This is truly a plant with multi-season interest.
Carex typhina is on the DNR’s special concern list, so we do not advocate collecting plants in their native habitat. Please buy your plants from a reputable native plant nursery.
If you are looking for a conversation piece for your garden, hop sedge will start tongues wagging. Carex lupulina sends forth an odd-looking fruiting structure reminiscent of hops in June. The 3/8 to 1/2 inch pointed perigynia radiate from the stem in a star-like pattern. Two or three clusters of perigynia subtend the terminal staminate flower. Fortunately, the fruiting structures persist for the entire summer. This plant is approximately 24 inches tall and has light to medium green foliage.
Like Carex typhina, hop sedge thrives in wet woods and prairies. Consequently, this plant does best in moist shade. One drawback of this plant is that it is slow to begin growing in the spring. Thus, patience is required.
Golden sedge lives up to its name in the color of its perigynia and not in the color of its foliage. This fine textured sedge displays spherical perigynia that turn from green to yellowish-orange as they mature. The perigynia look like miniature grapes and form in mid to late May. By the beginning of July, the perigynia start to dehisce.
Unlike the previous sedges, Carex aurea is best suited as a groundcover. This low growing sedge rarely exceeds 12 inches in height but it does spread to form 30 inch wide clumps in the sun. A word of caution—this plant is mildly to moderately rhizomatous and may spread and need to be kept in check. This plant is best used where you can allow it space to spread. Although this plant can be grown in sun or shade, it seems more vigorous in the sun, provided it receives adequate irrigation.
When we received Carex aurea plants for the Ornamental Grass Garden, they came with labels marked USDA Hardiness Zone 5. After enduring two winters at the Arboretum with very little snowcover, we believe this species can easily be planted in Zone 4. Furthermore, its native habitat in northern Minnesota suggests that the Zone 5 label is far too conservative.
If you are looking for a native sedge with spring ornamental potential, Carex sprengelii or long-beaked sedge fits the bill perfectly. This picturesque sedge blooms in mid-May and sends forth pendulous fruiting culms. The long green beaked perigynia give this species its common name. While the perigynia dehisce by the end of June, the plant remains attractive throughout the remainder of the summer. The foliage forms a clump of approximately 30 inches in width and two feet in height (without the flowering culms). The leaves measure 1/4 inch across.
This species is commonly found in sugar maple woods. Consequently, Carex sprengelii grows well in shade. However at the Arboretum, the plants placed in the sun appeared very healthy even after a period of drought.
|Carex aurea||Either||Moist prairies or woods in northern Minnesota||12”||30”||Moderately|
|Carex crinita||Best in sun||Wet prairies and wetlands in NE Minnesota||30”||30”||No|
|Carex lupulina||Shade||Wet woods and meadows in eastern Minnesota||24”||24”||Very slight|
|Carex sprengelii||Either||Dry to mesic forests throughout Minnesota||30”||36”||Very slight|
|Carex typhina||Shade||Wet woods in SE Minnesota||24”||24”||Very slight|
The Carex species listed above have good landscape potential. Besides being attractive, all five species have proven to be winter hardy as well as disease and insect resistant. Unlike many prairie sedges, these five species do not lodge and do not require much maintenance. Furthermore, very few people grow these species. This is an opportunity to inject a little novelty into your garden while at the same time supporting native species.
Since 1990, the Perennial Plant Association (PPA) has sponsored the Perennial Plant of the Year® program. Each year members select a superior performing perennial to highlight and promote. Nominations are made by members and winners are decided by ballot. Criteria for nomination includes it must perform well across a wide range of climates, be widely available and easy to propagate in order to supply demand, be relatively low maintenance and easy to grow so the average gardener has a high likelihood at being successful with it, and the plant displays ornamental appeal over a long portion of the growing season.
The 2008 Perennial Plant of the Year® winner is the hardy geranium or crane’s bill cultivar ‘Rozanne’. Although most of the 19 perennials selected over the years to receive this coveted distinction are reliably winter hardy in Minnesota, Geranium sp. ‘Rozanne’, unfortunately, is not. ‘Rozanne’ was included in the 2001 Herbaceous Perennial Trials at the University of Minnesota and was tested at several sites across the state. At these sites only 50‰ or less of the four plants at each site survived the winter with some sites having all plants winterkill.
Although ‘Rozanne’ is not a reliable perennial for the typical Minnesota garden (it is promoted as hardy to zone 5), it blooms prolifically first growing season and can be used as an annual. It blooms from late spring all the way to early fall and is very attractive and free-flowering with plants reaching 20-24 inches in height and a little more in width. Researchers at Michigan State University studied the flowering requirements of ‘Rozanne’. They discovered that ‘Rozanne’ does not require a specific photoperiod or vernalization treatment (a cold period) in order to flower, making ‘Rozanne’ a very easy plant to grow that flowers dependably across many climatic and environmental conditions.
Traits that separate ‘Rozanne’ from other crane’s bill include very large (up to 2.5 inches) violet-blue flowers with a white petal base, deeply cut, ornamental foliage that turns bronze in the fall, outstanding vigor, and an exceptionally long flowering period. Part of what may be allowing ‘Rozanne’ to flower so extensively and over a long period of time is that it is sterile and does not produce seeds. Without the hormonal signal of developing seeds the plant continues to initiate and develop new flower buds. Sterility has a similar result as deadheading spent blooms (removing developing seeds) does in order to encourage greater rebloom.
‘Rozanne’ was found as a natural hybrid of G. himalayense and G. wallichianum ‘Buxton’s Variety’ in 1989 in the garden of Rozanne and Donald Waterer in Somerset, England. It is a patented plant that is commercially reproduced under license using division, cuttings, and tissue culture.
Hardy geraniums including ‘Rozanne’ prefer garden locations with moderate to moist soil and partial to full sun. If they become overgrown and leggy by mid-summer, cut them partially back to promote new growth and a fuller plant. Fortunately, there are many reliably Minnesota-hardy crane’s bill cultivars, although most do not have as long a flowering period or as large of flowers as ‘Rozanne’. Some hardy geraniums that have proven themselves in university trials across Minnesota as being reliably hardy and also to having superior performance include G. x cantabrigiense cultivars Biokovo and Karmina and G. macrorrhizum cultivars Spessart and Ingwersen’s Variety. More information about the University of Minnesota Annual and Perennial trials can be found at www.florifacts.umn.edu
Many gardeners are conflicted when it comes to controlling pests or disease in their home vegetable gardens. Should they apply synthetic pesticides to manage an outbreak in their vegetables? Should they allow “nature” to take its course, do nothing to intervene and thereby sacrifice a season’s worth of tomatoes if severe disease sets in? Fortunately, there are more options than many gardeners realize. Options include control pest problems through cultural control practices like the use of disease resistant varieties, trap plants, crop rotation, the creation of habitat for beneficial insects, and mulch to manage weed, insect, or disease pressures.
There are situations when a vegetable may be particularly vulnerable to a pest or disease and a gardener may find themselves looking for an additional tool to keep plants healthy. For example, members of the cucurbit family (pumpkins, cucumbers, melons, and squash) are popular choices for home gardeners, but are prone to powdery mildew. The fungus responsible for powdery mildew is called Podosphaera xanthii.
Powdery mildews can be visually identified by the early stages of a whitish powdery growth, often starting on the undersides of older leaves. These spots of white powdery growth can expand to eventually cover most of leaf surface and cause the leaf to wilt and die. Spores are produced in the white spots and are spread by wind and insects to other leaves on the same plant and other cucurbit plants. The effects of powdery mildew can range from premature leaf drop or stunting and distortion of leaves to significantly reduced plant vigor and fruit of poor quality and flavor.
Traditionally, powdery mildew present on cucurbits would be treated with fungicides. There is now a biological control product on the market that could be used against powdery mildew. Biological control takes advantage of naturally occurring organisms that manage pests or diseases through parasitism, predation, or other natural mechanisms. These biological controls are acceptable for gardeners wishing to use organic disease control strategies. In the summer of 2007, an experiment was conducted at Cornercopia Student Organic Farm on the University of Minnesota St. Paul campus to examine the efficacy of one of these biological controls on powdery mildew on winter squash.
The product tested was Serenade Garden Defense, which contains Bacillus subtilis, a naturally occurring saprophytic (lives on decaying organic matter) bacteria present in soil, water, air, and decomposing plant material. In Serenade Garden Defense, B. subtilis has been suspended in an aqueous solution so it can be sprayed directly on foliage. These bacteria produce lipopeptide antibiotics that help them out-compete other microorganisms. Bacillus subtilis uses these antibiotics to kill or significantly reduce the growth rate of fungal spores and therefore wipeout populations of fungus causing plant disease.
The biological control spray was tested on the acorn squash ‘Tay Belle’ at Student Organic Farm. One week after planting, a scouting program was started to identify if, when, and to what extent powdery mildew was on these plants. This was continued on a weekly basis, with both sides of randomly selected leaves monitored for disease presence. It wasn’t until August 8th that a trace amount of powdery mildew was present and at that time the spraying program began. Following manufacturer directions, Serenade Garden Defense was then sprayed once a week on half of the squash plants in the test plots. The remaining plants served as controls and were left untreated for comparison. Powdery mildew continued to be monitored and the amount of fungus present was rated and recorded. The squash were sprayed until the first week of September when the squash had ripened and were harvested.
This experiment did not show an improvement in health or performance for the plants treated with Serenade Garden Defense. There was not a significant difference between plants treated or not treated with the biological control product for either the amount of powdery mildew present or the amount of squash harvested.
The results of this particular experiment should not deter a home gardener from researching and trying this or other biological control products. Serenade Garden Defense is registered for use on many other plant disease problems and in other crops and situations may prove beneficial. More information about this biological control product can be found at http://www.serenadegarden.com. For gardeners looking for organic or low impact fungicides to control powdery mildew, products with an active ingredient of either sulfur or potassium bicarbonate have been shown to be effective in other studies.
An interesting insect was discovered recently. A man in south central Minnesota in Watonwan county discovered some large caterpillars infesting some of the silver maples he was cutting down. They had created large tunnels about 3/8 - 1/2 inch wide in the wood. This insect, a type of carpenter moth, is known as a carpenterworm, Prionoxystus robiniae. In addition to maple, carpenterworms also attack a variety of hardwood trees including oak, elm, ash, black locust, cottonwood, and willow.
The larvae spend the winter in infested trees, pupating in spring. Because adult moths do not have chewing mouthparts, the larvae create exit holes from which brown pupae protrude. Adults are active in June and July. These stout-bodied moths have black and light gray mottled forewings. The female moths are considerably larger than males with a wingspan of 2 1/2 to 3 inches and are gray. The male’s wingspan is about 2 inches and it somewhat resembles a sphinx moth.
Females lay eggs in cracks in the bark which hatch into small pinkish red larvae that tunnel into the sapwood. As they create galleries they keep openings available to regularly expel large quantities of sawdust which can collect in noticeable piles at the base of infested trees. They eventually can move into the heartwood as they get larger. These larvae can grow to be as large as two to three inches long and are yellowish-white caterpillars with brown heads. Carpenterworms are long-lived in Minnesota, taking three to four years to complete their life cycle.
Carpenterworms are found throughout the U.S. and southern Canada. Heavily infested trees are at greater risk of breaking in wind storms and become gnarled and misshapen. In some areas of the country carpenterworms are considered a serious tree pest. In Minnesota, they are not considered a serious landscape pest. While they certainly are present in urban and forested situations, they do not appear to be common enough to require management.
Are you a “tree person”? Do you work with trees as a vocation or hobby? Do people ever seek your advice about tree care or other tree-related issues? If you answered yes to any of these questions then Minnesota needs your help.
Emerald ash borer (EAB) is an ash tree-killing beetle native to Asia that was first found in North America outside Detroit in 2002. Since 2002, EAB has been found in a number of other states – the closest being Illinois. While EAB has not yet been found in Minnesota, it is inevitable that one day it will be.
Detecting the presence of EAB as early as possible will be a key component in minimizing the impacts of this insect in Minnesota. The University of Minnesota Extension, the Dept. of Natural Resources (DNR), and the Minnesota Dept. of Agriculture (MDA) will be holding EAB First Detector Training sessions around the state during March and April, 2008. The role of EAB First Detectors will be to serve as a public contact for EAB information and to help resolve reports of EAB infestations in Minnesota.
EAB First Detectors must attend a one day training session on emerald ash borer and commit to being involved with the program after completing the training. Training will include presentations as well as hands-on training with materials. The one day training sessions will include information on:
1) How the Federal First Detector Program works
2) The importance of ash in Minnesota
3) An update on emerald ash borer
4) How to distinguish EAB and its signs/symptoms from look-a-likes
5) What should homeowners, woodlot owners, etc. be doing about EAB now
6) What will happen when EAB is found in Minnesota
7) How to handle reports of EAB / symptomatic trees
EAB First Detector training sessions have been scheduled for March 27 in Rochester, March 31 in Cloquet, April 3 in Mankato, April 7 in Andover, April 8 in Marshall, and April 10 in Fergus Falls. Applications must be post-marked or emailed by March 19.
A brochure describing the training as well as the application are available at: www.mda.state.mn.us/invasives/eab or by contacting the Arrest The Pest Hotline at 651-201-6684 in the Twin Cities Metropolitan Area or 888-545-6685 throughout Greater Minnesota.
Continue to sow seeds indoors to raise your own transplants of flowers and vegetables. Starting ones own transplants from seed can allow for a greater selection of varieties than what one may find as transplants in the garden center come May. In order to prevent seedlings from becoming leggy provide plenty of light, good air movement, moderate temperatures (too warm of conditions can encourage stretching), moderate moisture, and for some species consider pinching to encourage well-branched, bushy growth.
In March many garden centers receive packaged bulbs, bareroot divisions of herbaceous perennials, and bareroot plants of woody perennials like roses, blueberries, and raspberries. Plants are bagged in sawdust, peat, shredded cardboard or other substances and are shipped across the nation usually arriving in Minnesota while snow is still on the ground. Upscale garden centers will often refrigerate these dormant plants to preserve their quality before consumers purchase and plant them. Garden centers with fewer resources will display them right away at room temperature. They will begin to grow within packages and start to deplete their limited energy reserves. Consider purchasing these dormant plants soon after they arrive at the stores and keep them cool (typically 35-55oF using a refrigerator, unheated basement, or root cellar) and dormant at home until you are ready to plant them.
Branches of early-flowering shrubs like forsythia, pussy willow, flowering almond, and hardy quince and early-flowering fruit trees like apples and cherries can be cut and forced into flower inside to give us a preview of spring. Flower buds on these species are already formed the season before and are ready to continue to develop as temperatures warm up. Treat cut branches like typical cut flowers by recutting the stems when placing branches in vases to allow for good water uptake and replacing the water periodically and using floral preservative.
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David C. Zlesak, Ph.D.
Regional Extension Educator