Cooperative Extension Publications

Marjorie Peronto, Extension Educator, University of Maine Cooperative Extension

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The trees and shrubs in our Maine landscape are plants that we expect to live for many years, often to outlive us. Recent research has debunked many myths related to the proper management of these plants.

• The Myth: Purchase the largest tree you can afford.

Current Thinking: In recent years, our perceived need for instantly mature-looking landscapes has resulted in a demand for planting large trees. However, research now shows that smaller trees establish their root systems more quickly after transplanting than larger trees. In one study over a ten year period, 1-inch-diameter trees, because they became established more quickly, actually outgrew trees that were 6 inches in diameter at planting time.

• The Myth: When planting a tree or shrub, I should dig a deep hole and amend the soil with compost and peat moss.

Current Thinking: The hole that you dig should only be as deep as the rootball, and two to three times as wide. For most woody plants, 90 percent of their roots grow in the top 12 inches of soil, extending out laterally up to three times wider than the drip line. If a tree or shrub is planted too deeply, the roots may not be able to get the oxygen they need, and the plant will probably slowly die.

Should you amend the soil in the planting hole? Not usually. If the soil in the planting hole is amended so that it is too different from the surrounding native soil, the tree’s roots may never extend beyond the planting hole. This results in a small root system that circles in the planting hole. If you have chosen the plant best suited for your location, it should adapt well to the native soil. So, in most cases, don’t amend the backfill at all. The exception is if you are planting in soil that is either extremely gravelly or extremely heavy (perhaps construction site fill), then amend the soil up to 25 percent by volume. This improves the soil enough for roots to grow, but not so much as to prevent them from entering the native soil.

• The Myth: When I plant a new tree, I need to stake it.

Current Thinking: Research has shown that trees that are not staked develop larger root systems, greater trunk diameter, and greater trunk taper than their staked counterparts. Small trees that are stable in the soil when swaying don’t need to be staked. Only stake newly planted trees in high wind areas, or when there is a limited root system as a result of digging and transplanting the tree. Even then, stake loosely, allowing the tree to sway somewhat in the wind, so it will develop normal trunk taper for resilience to future winds. In most instances, remove the stakes after one growing season.

• The Myth: I should fertilize my trees and shrubs every year.

Current Thinking: As long as you are getting some slow healthy growth on your woody plants, leave them alone. Research shows that slower growing trees are typically stronger and more resilient than trees pushed into rapid growth with applied nitrogen, such as trees growing in frequently fertilized lawns. A slower growing tree or shrub that is under moderate nitrogen stress makes more efficient use of water and nutrients, has a more extensive root system, and has higher levels of stored carbohydrates and natural defense chemicals, making it more resistant to insect pests and diseases. That having been said, if your plant’s foliage shows clear signs of nutrient deficiency, then some feeding may be called for. The best approach, in this case, is to test your soil or have a leaf tissue analysis done, find out which nutrient is causing the deficiency problem, and fertilize accordingly.

• The Myth: Watering my plants briefly every day is the best way to keep them moist.

Current Thinking: Frequent shallow watering causes your plants to develop very shallow root systems, leaving them much more vulnerable in times of drought. It is much better to give them a thorough, deep watering that saturates the root zone once a week, especially in the planting year. Consider setting up an inexpensive drip irrigation system that will deliver the water slowly over the entire root zone.

• The Myth: When mulching my trees, I should pile the mulch in a mound against the trunk of the tree.

Current Thinking: Piling mulch next to the trunk keeps the trunk moist, causing the bark to rot, leaving it very susceptible to insect and disease infestation, as well as burrowing mice. Mulching is great for conserving soil moisture and keeping weed growth down if it is done right. After planting, spread an organic mulch (shredded bark, pine needles, compost, etc.) 2 to 3 inches deep over the entire planting area, starting two inches away from the trunk of the tree.

The benefits of mulch around our landscape trees and shrubs are directly related to many of the recommendations mentioned above. Over time, mulch improves soil structure in the root zone while conserving soil moisture and slowly adding nutrients to the soil as it decomposes.

The landscape management practices discussed in this article focus on recommendations designed to promote healthy trees and shrubs that are resistant to insect and disease attack and that will thrive in the sustainable landscape. Of course, selecting the plants that are best suited to your site is the single most critical factor for long term success.

Information in this publication is provided purely for educational purposes. No responsibility is assumed for any problems associated with the use of products or services mentioned. No endorsement of products or companies is intended, nor is criticism of unnamed products or companies implied.

© 2011

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