REESER MANLEY

Advice on planting container-grown trees and shrubs

Posted Sept. 30, 2011, at 5:13 p.m.

“The best time to plant a tree was 20 years ago. The next best time is now.”

— Chinese proverb

Unlike the hard-wearing daylily that can be uprooted time and again, woody plants should grace the garden space we give them for decades. Their planting should be approached thoughtfully and methodically.

At planting, a container-grown tree or shrub has less than 20 percent of the absorbing roots as the same size plant established in the garden. The gardener’s goal at planting is to promote rapid root growth and reduce the water stress imposed by a limited root system. Soils in Maine are often compacted or poorly drained, conditions that give woody plant roots a hard time. Compaction of the soil prevents adequate aeration of the root zone, while too much water drowns roots. Neither of these conditions are remedied by planting in a hole barely larger than the root ball.

Roots of plants placed in small holes soon reach the compacted native soil and, unable to penetrate it, begin to circle in the hole, much like the circling that occurs when roots meet the impenetrable sides of a pot. Circling roots can become girdling roots, cutting off water flow to the plant like a crimp in a garden hose.

Small planting holes surrounded by compacted soil may also drain slowly after a hard rain. Roots die in the waterlogged soil.

A current trend designed to avoid these problems involves planting trees or shrubs in large beds. This technique provides roots with a larger area in which to grow before encountering native soil that might be too compacted or poorly aerated.

And so the planting day begins by outlining the bed’s border with a section of garden hose. Make the bed at least ten times as wide as the root ball, wider if possible, and no deeper than the depth of the root ball. As you work, think about the roots that will soon be growing outward from the trunk in all directions, absorbing water and nutrients from the top 12 inches of the soil.

For particularly clayey or sandy soils, increase the organic matter content 25 percent by digging a three-inch layer of compost into the top 12 inches of the soil. The compost should be fully decomposed, since bacteria working on unfinished compost tie up nitrogen in the soil. If a recent soil test indicates a need to adjust the pH, the needed lime or sulfur can be worked into the soil at this point.

Give the new plant a thorough watering before gently removing it from the pot, always handling the plant by the root ball, never by the trunk or stem. Carrying or lifting a tree by the trunk can sever young roots and root hairs.

If the plant has been in the pot too long, it may have roots circling both the sides and bottom of the root ball. Using the edge of the spade, slice off the bottom mat of circling roots and toss it on the compost pile. Then, using your fingers, gently tease the circling roots from the sides of the root ball so that they spread outward in all directions.

Now form a planting hole in the middle of the bed. The hole should be no deeper than the root ball but at least three times as wide. This is easy digging and I often do it by hand for small plants, removing the loosened soil one handful at a time, breaking up clods, gently moving earthworms out of the way.

Slope the sides of the hole toward the bottom, then use the edge of the spade to score the sides of the hole; smooth, slick sides can act as physical barriers to root growth. And remember, the root ball should rest on undug soil to prevent the plant from sinking after it is planted, so tamp down any loose soil in the bottom of the hole.

Place the plant in the hole with the roots spreading outward and begin to backfill with the soil removed from the hole. When the hole is one-third full, check to make sure that the plant is straight and at the proper depth, then resume adding soil until the hole is filled. The top of the root ball should be level with the soil surface. Water the new plant thoroughly to eliminate large air pockets in the soil.

The finishing touch is a 3-inch deep mulch of aged compost or shredded leaves over the entire bed. This mulch will break down over the course of a growing season, providing all the fertilizer that the plant needs, and you will need to replace it each year. Avoid chunky bark mulches that take forever to break down and feed the soil.

Also, avoid “volcano mulching,” piling mulch against the trunk, which traps moisture against the bark causing disease and decay. You should always be able to see a ring of bare soil around the base of the plant.

Spend the better part of a day planting a single tree, working slowly with spade and hands. Then spend the rest of your life watching it grow.

Next week: planting bare-root and balled-and-burlapped plants.

Send queries to Gardening Questions, P.O. Box 418, Ellsworth 04605, or to rmanley@shead.org. Include name, address and telephone number.

 

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