Shade trees are both an aesthetic and financial asset, but keeping trees healthy can be challenging. Careful tree selection, planting and maintenance are needed to keep trees healthy.
The first thing a tree needs is space. Trees need as much room for their roots as you expect to have foliage on top. Most roots will be in the upper two feet of soil, though some species also grow deep tap roots. The roots need oxygen as well as water, so keep a well aerated soil surface that is at least 1.5 times as large as the crown of the tree is wide.
If you have poor soils, it would be ideal if you would plan a year in advance about planting a new tree. That year would give you time to not only dig a large a hole (three feet deep and at least 1.5 times as wide as the root ball) but to backfill it with a mix of original soil and 30-40 percent composted organic debris. Amended soils settle, so waiting a year reduces the risk of a tree shifting after planting. In addition, any newly planted tree taller than three feet will benefit from being stabilized by a well-anchored stake that is as tall as the tree and attached with a cord at about two-thirds of the tree height. Pad the cord where it attaches to the tree and keep it loose enough to allow for growth.
If planting a tree with a burlap-covered root ball, cut vertical slits in the burlap three inches or more apart once the tree is in the hole to allow for proper root growth.
Don't add more than two inches of soil over an existing tree's root system in any given year, or the roots will have difficulty getting air. Keep the new soil at least two feet away from existing trunk that are larger than six inches in diameter.
Especially for new trees, water often and deep during summer. Tree seedlings or balled and burlaped trees need to grow enough roots to supply the tops with water during summer heat. Shallow watering promotes shallow roots. Since most soils will only allow for water penetration of about one-inch per hour, using a drip system or soaker hose that applies about a gallon an hour, left running for 24 hours or more at a time, will create a deep water profile in the soil. This will also prevent salt accumulations in the rooting zone, which could eventually poison your tree.
Fertilize only in the spring with a well balanced fertilizer. Most lawn fertilizers consist mainly of nitrogen, which stimulates growth but not drought hardiness or defense mechanisms in trees. Apply a generic 10-10-10 (numbers denote the proportions of nitrogen, phosphorus and potassium) fertilizer after your last expected spring frost with ample water on the soil just inside and outside the tree canopy. Specialized fertilizer for trees (that have additional other nutrients) also works well, because sulfur and iron are common deficiencies on Montana soils that can cause tree foliage to appear yellow or pale green.
Prune your trees properly, which for deciduous trees is best done in late winter before budburst or mid-summer. Most shade trees want to be lollipop or umbrella shaped for maximum energy production and water conservation. Deciduous trees should generally be pruned up, which means removing lower and inner branches so that you can walk under the trees and look up into a cathedral-like tree canopy.
Top-pruning to shorten a tree creates tangled growth and weakened crowns that fail during windstorms if done improperly. Occasionally, a tree will need the top pruned because of obstructions like power lines. For shortening deciduous trees, a branch should be pruned back to where another substantial branch forks off. This enhances the natural shape of the tree and protects its structural integrity versus arbitrarily lopping off the top to some designated height. If the tree is too large for you to prune safely or you are uncertain where to cut, hire a professional.
Conifers or "evergreens" prefer to be cone-shaped. Every year one main leader grows upward and a new "whorl" of side branches grows off last year's leader growth. To remain healthy, their foliage needs full sunlight, so widely spaced trees can maintain foliage all the way to the ground. If lower branches become shaded, they die. Lower branches that die or are pruned off will never grow back with any size. Pruning for health and shape is best done in early summer before the new growth has hardened. Larger branches can be pruned any time of the year. When shaping a conifer, leave some new growth. It is almost impossible to keep a tree the same size and healthy when it is genetically programmed to grow big. Healthy conifers will keep their needles for three years, thus leaving new needles every year is essential to maintain healthy needles.
Evergreens such as pines, spruces and junipers can have tops pruned back somewhat without significant damage to the tree if a shorter squatter tree is desired, and a healthy crown is available to work with. Typically no more than one-third of the green crown should be pruned off. Spruce trees, which have short needles with very prickly ends, are notoriously shallow rooted, making them very susceptible to being tipped over by high winds when they get taller than 40-50 feet. Pruning the tops of these trees back a little will promote wider denser trees that are less likely to fall in a wind storm. However, topping will change the shape of the tree so only do this with careful consideration.
When in doubt about any pruning, consult with a qualified professional arborist. Pruning and caring for trees requires knowledge, skill and concern for your wishes. Always ask for references and look at previous pruning work. Call your local Extension agent if you have questions.
Do not use tree injections unless your tree has a problem that is readily evident to you and has been diagnosed by an expert. Drilling holes into trees to inject a systemic insecticide or fungicide harms the tree. It is only warranted in specific situations as an expensive option to save the tree from an existing insect or disease attack or proven local threat. In addition, injections typically only work for deciduous trees when applied in early spring and summer, and do not work with most conifers. Never use injections as a means of fertilizing. If your tree looks healthy to you, it probably is and does not require anything other than occasional watering and mild uses of fertilizer. An unsolicited knock on your door by someone who says your tree is sick and needs an injection, probably only wants easy money. If in doubt, call your Extension office for advice.
Trees are beautiful and useful. A large deciduous tree planted on the south-west side of a house can keep your house 10-20 degree cooler in summer yet allow for the sun to warm your house after their leaves have dropped in the winter. A dense conifer such as pine, spruce and juniper planted on the windward side of your property also acts as a privacy screen and windbreak. Energy-use studies have shown that windbreaks reduce heating costs by 30 percent during the winter.
Choose and maintain your trees wisely.
