Choosing landscape evergreens
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Planting and caring for evergreens requires a considerable investment of time and money, and so it is important to make the right decisions when choosing these plants for your yard.
To choose wisely, you need to know two basic pieces of information. First, you need to know the ultimate size of the space that you want filled by the evergreen, and second you need to be sure that the species or varieties you are considering can grow vigorously in the climate and site conditions of your property. This publication is designed to provide guidelines to help you select evergreen trees and shrubs for Minnesota landscaping.
Learning about the habits and needs of evergreens is worth the effort. Nursery grown evergreens of landscape grade are expensive. Years of care are required to produce well shaped tops and ample root systems before trees are sold. More years of care will be required after the evergreen is transplanted to a landscape. If you make the right choice at the beginning, not only will you save time and money, but your landscape evergreens will provide years of pleasure.
Evergreens as design materials
An obvious first consideration in choosing evergreens is how they will look in the landscape. You need to take into account each plant's size at maturity, shape, color, and texture before you plant.
Most Minnesotans admire and appreciate native evergreens in the state's forested lands. Pine, spruce, fir, and arborvitae, whether frosted with snow or tipped with new spring growth, symbolize the beauty of the north. As most vacationers know, these native species are often enormous trees at maturity. Spruce, fir, and arborvitae are pyramid-shaped evergreens that may cover a circle 30 feet in diameter when they reach full maturity. Pines are also pyramid-shaped as young trees, but as they mature they often lose lower branches, resulting in open space beneath. Depending on the species, pines can reach 50 feet or more in height. Pine roots fill a large circle of soil under their foliage, making it difficult to grow turf and other plants underneath these trees. Most home properties have limited space for evergreen trees such as these. One large evergreen tree with thick foliage touching the ground can shelter the northwest exposure of most town or suburban home properties, but may be too large for a city lot. Where a group of evergreen trees might seem more effective than just one tree, a good choice would be smaller upright junipers or columnar arborvitae because they are often more in scale with residential sites. These evergreens will mature at 20 to 30 feet, with a spread of 5 to 10 feet, depending on the variety.
Evergreen shrubs require careful spacing, especially since they are so often planted at doorways or at the base or foundation of a house. Juniper shrubs with horizontal shapes can spread to five or six feet in a few years; heights vary considerably according to the cultivar (cultivated variety). An 18-inch high skandia juniper is far more useful under a ground level window than its 5-foot relative, savin juniper. Japanese Yews are often pruned tightly to keep them at a desired height or width, but some selections will grow into 20-foot trees or very wide shrubs over time.
It is important to remember that plants for sale in nurseries are young/small enough to handle and offer at a price customers will pay. Differences in these evergreens are not apparent to customers unfamiliar with variety names. Do not make the mistake of expecting Welch juniper or pyramid arborvitae to remain the dwarf shrubs they appear to be in the nursery sales lot. Check the catalogs, ask for fact sheets at your county extension office, consult with experienced nursery people, and study plantings in your own community. You need to know which tree or shrub best fits the space you want to fill with evergreen foliage.
Figure 1. Common evergreen shapes.
Evergreen trees and shrubs are conspicuous in landscape designs. Crowded, upright forms can block windows and smother a building with oppressive foliage. Too many evergreens can make an outdoor space gloomy and depressing. On the other hand, a south facing mass of pines can form a winter suntrap, reflecting light and pleasant warmth to a driveway, walk, or house beyond. The strong outline of a columnar evergreen calls attention to a view or emphasizes a pathway. But such an exclamation point is not suitable for framing a garage door or calling attention to a power pole. A soft, horizontal line of spreading junipers or yews without any distraction of varying shapes or sizes can be a satisfying transition from house wall to ground level.
Color and texture
The different colors and textures of foliage, bark, cones, or berries should also be considered in selecting evergreens. There are silvery blue juniper varieties (trees, shrubs, or ground covers) that are often effective as a contrast to redwood surfaces. Dark green Japanese yew, the female plants bearing red berries in fall and winter, are handsome against many colors of brick. Scotch pines' cinnamon orange bark and bluish green needles are prettier in winter than the purplish brown eastern redcedars. Deep green spruce or balsam fir contrasted with red maples present a pleasing scene.
Color and texture variations must be carefully used. Any closely planted mixture of textures and shades of green will appear not as a harmonious group but as a crowded collection of individual trees. Plant conspicuous evergreens only occasionally, when an eye-catching specimen is particularly needed.
Landscape plantings, whether for home properties or large public grounds, are most satisfying when a clear pattern is apparent to people using the space. Simplicity and serenity are important for outdoor design. Use the fewest possible varieties of evergreen plants and select them for an obvious purpose. For example, you may want them to provide four season beauty and year- round privacy for outdoor living spaces or views from windows and glass walls.
Climate and site requirements
Cold hardiness is the first test a plant must pass to be considered suitable for Minnesota landscaping. The USDA plant hardiness map is a standard reference for approximate ranges of average annual minimum temperatures (see map). Minnesota is divided roughly in half between Zones 3 and 4, with a strip of Zone 4's milder temperatures along the shores of Lake Superior and pockets of Zone 2 in the far north.
Figure 2. Approximate ranges of average temperatures in Minnesota.
The northern United States is not all in the same zone. The climate of the Pacific northwest or New England, for instance, is modified by ocean currents and mountain ranges, whereas Minnesota is exposed to winter blasts of Arctic air. Many plants listed in nursery catalogs as suitable for northern states or Canada do not survive in Minnesota. Reputable mail order nursery firms identify zones of cold hardiness in their catalogs, and experienced Minnesota nursery people can offer firsthand information on winter survival of evergreen plants.
Large scale temperature zone divisions are sometimes not precise enough for choosing evergreens for long life and vigor. Plants may grow well in extreme southern Minnesota and be injured by cold in Minneapolis even though both are in Zone 4. The term "microclimate" is used to describe small areas that provide slightly different growing conditions than those normally found in a particular geographical area. Evergreens exposed to wind on hilltops or on the western sides and corners of buildings are stressed both by cold and drought. Plants in a sheltered setting may grow in localities outside their normal hardiness zone, but an extremely cold winter may kill such exotics. Use a hardy plant such as mugo pine or savin juniper in exposed locations instead of less tolerant species. Black hills spruce will grow well in colder, dryer locations, but white fir needs a moist, rich soil and milder temperatures. These differences are important when choosing a specimen evergreen tree for your property.
In addition to survival, resistance to injury is another cold hardiness requirement for evergreens in a landscape. Tip kill (dieback of upper shoots and branch ends) and winter burn (browning of foliage) are symptoms of winter damage. Although the plants live, they are disfigured until pruning. New growth can improve appearance over time. During some winters, evergreens are damaged by fluctuations in temperature that cannot be prevented, but planting evergreens in locations exposed to the warmth of the afternoon sun on bright winter days is not prudent. When the sun goes down, or moves behind an obstruction, the plant may suddenly be plunged into sub-zero cold, with resulting damage. If an evergreen is needed in such an exposed place, check with local nurseries and observe successful plantings in your own community before choosing a variety. Maney juniper, for instance, seems to be more resistant to winter burn than pfitzer juniper or Japanese yew. Welch juniper is usually less affected by tip kill than spiny Greek or Irish juniper, both sometimes attempted in Minnesota.
Soil and moisture requirements of evergreens hardy in Minnesota vary enough to allow selections for many different site conditions. Available moisture is as important as temperature for plant hardiness. Well-watered evergreens often survive when other plants fail, but those struggling through a dry summer in weakened condition are often dead after a cold winter. Dwarf junipers and Japanese yew in foundation plantings close to house walls, or overhung by wide eaves, often die from this combination of drought and cold.
More rainfall and snowmelt usually occur in eastern Minnesota than in the west, but within each area there are soils that differ in their ability to hold moisture for plant growth. Sandy soils are droughty, while silts and clays may be so poorly drained that some plant roots lack sufficient oxygen. Well-drained loams are ideal for most evergreens, but pines and junipers are more tolerant of sandy, dry conditions than spruce, fir, and arborvitae. Heavy soils, if drained, grow magnificent white fir at Worthington in southwestern Minnesota. Arborvitae and black spruce will grow in the wet soils of ditch banks, low-lying spots, pond edges, and lake shores, where other evergreens fail. Balsam fir grows well in locations that are damp for part of the year.
Most Minnesota soils are fertile and acid enough for evergreens suited to existing temperature and moisture conditions. However, soils of western Minnesota, and other places where limestone is the underlying rock, may have a high pH*. In general, evergreens do not like a pH above 7. This condition may cause a tie up of soil iron, stunting the plant and yellowing the foliage. Arborvitae, junipers, ponderosa pine, and white spruce are generally tolerant of the higher pH soils in Minnesota.
One way to improve your chances of growing healthy evergreens is to copy forest conditions. Evergreens in nature are mulched by their own fallen needles and other forest litter. Soils are usually moist, modified with rotting organic matter, and protected against sudden temperature changes. If your landscape design can include mulched planting areas to improve soil moisture relationships and prevent competition from weeds and grass, your evergreens will grow better. Extra watering will still be needed in dry weeks during the growing season, but plants will not be stressed as much as those growing over bare ground or mowed lawn.
Some evergreens to consider
Light requirements for healthy evergreen growth must be accommodated by selecting the appropriate plant for each location. Canada hemlock and Japanese yew will grow in shade in Minnesota. However, Canada hemlock requires shelter from wind and a moist soil. Several successful cultivars of Japanese yew are offered by Minnesota nurseries, but moisture and protection from winter sun are usually advised for these plants. If other conditions are suitable, balsam fir, white pine, and douglas fir will grow where light may be filtered for part of the day. Junipers, spruce, and all other pines need full or almost full sunlight. Shape, growth rate, color, and pest tolerance are all diminished by planting these species under other trees or in the shadow of buildings.
|Evergreens for problem sites|
|Clay soil||Arborvitae, Austrian pine, ponderosa pine, white fir|
|Sandy soil||Scotch pine, mugo pine, junipers|
|Wet soil||American arborvitae, balsam fir, black spruce|
|High pH||Arborvitae, black hills spruce, mugo pine, ponderosa pine, junipers|
|Windy, exposed||Black hills spruce, jack pine, mugo pine, red pine, ponderosa pine, Rocky Mountain juniper, savin juniper, eastern redcedar, douglas fir|
|Partial sun||Arborvitae, balsam fir, douglas fir|
|Shade||Canada hemlock, Canada yew, Japanese yew|
A note on Colorado blue spruce
Colorado spruce, including Colorado blue spruce, has, in the past, been a favored tree in Minnesota because of its attractive size, shape, and (sometimes) blueish hue, but no more. Over the past 20 years evidence has accumulated showing that the Colorado spruce was not meant for our climate. Colorado spruce tends to do well for about 20 or so years in our climate and then suffer because of Rhizosphaera needle cast and Cytospora canker. Small, dwarf cultivars and slow-growing Colorado spruce are more likely to do well over time. In the southwestern portion of the state these trees are also more likely to do better. Nonetheless, Colorado spruce is not typically recommended for Minnesota gardens because of the problems associated with them as they mature.
Disease and insect problems
Pest resistance is another topic worth studying before choosing landscape evergreens. No tree or shrub is completely immune to insect or disease attack, but experience with evergreens commonly grown in Minnesota has proved some to be less susceptible than others. Proper location and good cultural practices are often extremely useful in minimizing pest damage. Investigating the probability, symptoms, and necessary control measures of frequent pests can help you select evergreens to fit your maintenance plans. Consult your local Minnesota Extension office, the Minnesota Landscape Arboretum, or local nurseries about pest problems with any evergreen tree or shrub you are considering.
Useful notes on some landscape evergreens
|Trade name of evergreen||Hardiness zone||Growth rate||Maximum size (ft.)||Shape||Light requirements|
|Globe||3||Slow-med||5||Globe||Full sun - full shade|
|Techny||3||Slow-med||15||Pyramid||Full sun - full shade|
|Douglas fir (not a true fir)||4||Med||60||Pyramid||Full sun|
|Balsam||3||Slow||50||Pyramid||Full sun - part shade|
|White||4||Slow - med||50||Pyramid||Full sun|
|Canada||3b||Med||40||Pyramid||Part shade - full shade|
|Savin||3||Slow||5 x 10||Spreading||Full sun - part shade|
|Green Globe||4||Med||4x 4||Globe||Part sun|
|Rocky Mountain||3b||Slow||15 x 8||Cone||Full sun|
|Wilton Carpet||4||Slow - med||2 x 8||Spreading||Full sun - part sun|
|Prince of Wales||4||Slow - med||4 x 8||Spreading||Full sun - part sun|
|Pfitzer||4||Slow - med||4 x 6||Large spreading||Full sun - part shade|
|Sargent||4||Slow-med||2 x 8||Spreading||Full sun - part shade|
|Scotch||3||Slow - med||50||Pyramid||Full sun|
|White||3||Med||60||Pyramid||Full sun - part sun|
|Black Hills||2||Slow||40||Pyramid||Full sun|
|Norway||3b||Med - fast||60||Pyramid||Full sun - part sun|
|Japanese Spreading||4||Slow||5 x 6||Large spreading||Part shade - full shade|
|Japanese Dwarf||4||Slow||3 x 5||Large spreading||Part shade - full shade|
|Taunton Spreading||4||Slow||3 x 5||Large spreading||Full sun - full shade|
This page was created in partnership with the University of Minnesota College of Agricultural, Food, and Environmental Sciences and University of Minnesota Extension.