Evergreen Trees and Shrubs
Evergreen trees and shrubs are an integral part of landscapes in the Upper Midwest because of the many unique benefits they have to offer. They make excellent screens, reduce noise and are key elements of windbreaks. They also provide shelter and food for a variety of wildlife. Their foliage is present even in winter, providing year-round interest in landscapes.
To look their best throughout their life, evergreens need proper planting, watering, fertilizing, mulching and pruning as soon as they are planted in the landscape.
Click on any of the following headings and link to chapters that explain selection and maintenance of deciduous shrubs:
Select evergreen species based not only on their appearance, but on their purpose and mature size. Too often, evergreens are not given enough space to reach their natural mature size, and end up crowding other plants, sidewalks, and buildings. Therefore, the first step in choosing an evergreen is to analyze the site conditions and to place evergreens as part of an overall sustainable design.
For more information on evaluating the existing site, see Site Survey
For more on selecting trees based on site and plant characteristics:
Elements of Design
While many evergreens are slow growing, others can grow quite quickly once established. Most evergreens, such as spruce trees, look best if allowed to grow naturally with no shearing or regular pruning. Be sure there is enough room on all sides for such trees to spread out and achieve their mature beauty. Also be sure there is adequate room for roots to spread out. If tree roots are confined to a small area because of buildings, walks, driveways, roads, etc. (roots will not grow under hard surfaces), the root system will eventually be too small to provide for the size of the tree. The tree will then stop growing, decline, and eventually die.
For foundation plantings or shrub beds, there are many dwarf evergreens from which to choose. Be sure to match plants with the light, moisture and soil conditions in your landscape. Most evergreens require well-drained soil. Arborvitae, however, can tolerate wetter areas. Most evergreens also prefer a sunny location to do well. Arborvitae can tolerate light shade, and Japanese yew and hemlock will grow in shade. In fact, yew and hemlock will burn in afternoon winter sun and are best planted on north or east sides of buildings.
From a design standpoint, avoid planting single columnar or pyramidal evergreens on corners of buildings, as they will accentuate the vertical line and move the eye up and out of the landscape.
For more information:
Choosing Landscape Evergreens
Unlike deciduous trees and shrubs, evergreens are rarely available as bare root stock, except as very small seedlings. They are usually available throughout the growing season as balled and burlapped or container-grown plants.
When selecting plants at the nursery, be sure the foliage looks healthy and is not "off color" (graying, yellowing, browning). Once an evergreen needle is brown, it will not turn green again. Browning needles may be evidence of drought stress or a disease. Because evergreens don't wilt like deciduous plants do, they often don't show the symptoms of drought stress or diseases until long after the damage has been done.
Choose evergreen trees that have a single central leader and good branch structure. Inspect the trunk for damage or oozing sap. If possible, purchase trees that have not been sheared, as if for Christmas trees. Sheared trees will take several years in the landscape to regain their natural shape once regular shearing ends.
Evergreens should be planted in spring, summer or early fall. While deciduous plants can be planted later in fall, evergreens benefit from having some time while the soil is relatively warm to start to become established. If evergreens are planted too late in fall, they will not be well-hydrated and may "burn" or brown during winter. This is due to moisture loss from foliage that cannot be replaced by the roots.
Balled and burlapped or containerized evergreens can be planted the same way as deciduous plants. For detailed instructions on planting, see Planting Bare Root, Containerized and Balled and Burlapped Trees and Shrubs.
Most evergreen trees rarely require any pruning, provided they are planted where they have adequate space to grow. Evergreen shrubs, however, can sometimes benefit from regular pruning that keeps them from getting bare and overgrown. Most evergreens, other than pines, are best pruned before spring growth begins. They can also be pruned in mid-summer, when they are "semi-dormant".
Avoid shearing evergreens, unless they are part of a formal garden or hedge. Instead, maintain the natural form of the shrub by heading back the longest shoots to a natural spot or vigorous bud. Unlike deciduous plants, evergreens do not readily sprout from a cut branch. Be sure to not make any "holes" in the plant's structure when pruning, as it may take several years to fill in.
- Pines rarely require any pruning. To reduce growth and limit plant size, you can remove up to 2/3 of the length of "candles", or new, soft growth in late spring. Mugho pine shrubs can also be sheared regularly for a very formal effect. However, this should only be done as part of an overall formal design, as they will look out of place in an otherwise naturalistic landscape.
- Upright junipers can be pruned into formal shapes, or selectively pruned to maintain a desired shape. If trying to control the shape or size of the plant, pruning should be done each year, removing 2/3 of the new growth. Spreading and creeping junipers can be kept looking their best by removing two or three of the longest, thickest, most vigorous branches each year. Cut back to the next main stem to encourage young growth. If branches are allowed to get thick and a lot of woody stems are visible, they can be cut back to the base. However, it will take several years for new growth to fill. Always maintain the horizontal form of creeping and spreading junipers, and do not shear in a formal way.
- Yews typically have two flushes of growth each growing season. They are best pruned in spring, before growth starts, and again in mid-summer. They can be sheared formally if part of a formal landscape, or they can be selectively pruned to maintain a natural form and keep plant size smaller and vigorous.
- Arborvitae should be pruned in early spring or mid-summer. Over-grown plants can be severely cut back and re-shaped, but will take several years for new growth to be produced and fill in. While arborvitae can tolerate formal shearing, they can also be left unpruned if enough space is available.
- Spruce are rarely pruned, unless their growth is too rapid and their size must be limited. Prune unbranched tips of side branches back by 2/3 their length. This will help keep the tree from getting wider.
- If the central leader of a spruce or fir is damaged or destroyed, you can encourage a new leader to form. Trim back the damaged leader to about 2 inches above the first side shoot. Carefully tie one side shoot to the stub of the old leader so that it is pointing upward. Over time, the side shoot will take over as the central leader. If ever there are two leaders forming, prune away the smaller, weaker one.
Newly planted evergreens should be watered regularly during the first year after planting. They should be soaked by rain or supplemental watering once a week, or more during hot, dry weather on sandy soils. Keep watering right up until the ground freezes, usually in late November in the Minneapolis/St. Paul area. It is important that evergreens are fully hydrated going into winter. Because evergreen foliage is retained through winter, it is exposed to drying winter winds. With frozen ground and roots, plants cannot replenish that moisture and can "burn" or brown by spring.
Most evergreens require well-drained soil, and overwatering them will result in stress and damage to roots. Feel the soil near the shrub about 1-inch deep. If the soil feels dry, thoroughly soak the soil around the root zone. Avoid overwatering - it can be just as harmful as underwatering. Plant roots need oxygen as well as water. Too much water fills the air pockets between soil particles and creates an anaerobic environment. This can result in root rot and an environment favorable to other pathogens such as fungi and bacteria.
Applying organic mulch around the base of evergreens can help retain moisture, control weeds, moderate soil temperature, and give a nice appearance to the landscape. Most any organic material can be used as mulch, including shredded wood or bark, wood chips, pine needles, cocoa bean hulls, straw, ground corncobs, or any other available organic matter.
To be effective, mulches should be applied so that when settled, it is 3-4 inches deep. However, be sure to pull mulch away from the trunk or stem of the plant. Mulch left against the bark can cause moisture buildup which can rot the bark and cause severe injury to the plant. Do not create a "volcano" of mulch around the trunk, but instead place the mulch in a "donut" form. Do not use a landscape fabric or plastic when using organic mulches.
It is important to keep mulch away from tree trunks
to avoid retention of moisture against the wood and potential rot.
Inorganic materials often used as mulch, such as landscape rocks, can also be used. However, rock tends to absorb heat during the day and release it at night, which can be stressful for plants. Also, you will need to use a landscape plastic or fabric under the rock to control weeds, which you would not use with organic mulch.
For more information:
Mulching the Home Landscape
Evergreens should be fertilized in early spring or late fall. Depending on the results of a soil test, a high nitrogen fertilizer is usually best, such as 12-6-3 or 16-6-6. Follow package instructions for what rate to apply, but usually a rate of 1/3 pound per foot of height or spread is appropriate. Dig the fertilizer into the soil around the base of the plant, being careful to not damage any roots, and always water well after application.
Mature, large evergreen trees rarely need fertilizer. However, if they are showing nutrient deficiency symptoms, such as off-color needles, or if you want to encourage growth, fertilizer might be helpful. You can also bore holes in the soil around the tree 12-15 inches deep, and divide the recommended amount of fertilizer amongst the holes. Fill the holes with sand or soil, and water well.
A common misconception is that evergreens need acid soil to do well. A neutral pH in the 6 to 7 range is ideal for most evergreens. Unless your soil has a high pH, it is not necessary to use an acid fertilizer on your evergreens. However, a high pH, such as 7.8 or higher, can cause some evergreens such as white pine to become chlorotic because they are not able to take up iron from the soil.
For more information:
Tree Fertilization: Guide for Fertilizing New and Established Trees in the Landscape
Preventing Pollution Problems from Lawn and Garden Fertilizers
Plant Injury Due to Turfgrass Broadleaf Weed Herbicides
Living Snow Fences
Energy Saving Landscapes
To help evergreens survive through the winter, be sure to plant species that are hardy for the area. Water evergreens and all plants up until the ground freezes. Evergreen needles are exposed to drying winter winds and must be well-hydrated throughout the winter months. Dehydration may result in burning or browning of the needles by spring.
The buildup of ice or heavy wet snow may cause damage to evergreens during winter. However, in most cases, freezing rain buildup on evergreens will not harm them in the long run. Branches may sag, but they are typically flexible enough to withstand the weight and will bounce back once the ice or snow melts or falls off. If ice buildup is less than 1/8 inch thick, it is best to leave it alone and avoid the risk of damaging branches while trying to remove the ice.
In cases of extreme ice buildup where there is a risk of branches breaking because of the weight, it is helpful to carefully remove some of the ice. Use a rake handle or other round stick to gently tap the branches to remove some of the ice. You do not need to remove all of the ice, just enough to eliminate the threat of breakage because of the weight of the ice.
Avoid the use of ice-melting salt around evergreens, as it can cause damage both from spraying on the foliage and from building up in the soil. Also, avoid planting evergreens close to roads, drives or walks where snow may be piled which could cause breakage to branches.