Gardening Note #9

PLANTING TREES AND SHRUBS IN CLAY SOILS

Many folks mistakenly believe that digging a planting hole 3 or 4 times larger than needed, adding crushed rock to the bottom and rich topsoil as a backfill will solve all drainage problems. For a long time, this was the recommended planting method. Research has shown that holes dug in poorly drained clay soil will only fill with water and continue to hold this excess water over a long period of time, regardless of the size of the hole. When soils are saturated, the amount of oxygen available to plant roots becomes very limited. Planting this way creates a "bathtub without a drain" and the plants ultimately drown. This traditional planting method is the one usually shown on plant labels but it is not appropriate for the Cumberland County area unless your perk test tells you it is.

Poor drainage and improper planting are responsible for many planting failures. Test your drainage by doing a "perk test" when the soil is neither extremely dry nor extremely wet. Dig a hole in your yard about 12" deep and fill it with water. Check it regularly for the next 24 hours. If the test hole drains in 3-4 hours you have good drainage. 5-12 hours means moderate drainage, and plants susceptible to root rot diseases must be planted "high." 12-24 hours indicates that you should plant high, meaning plant "on" rather than "in" the ground. If you are in doubt about adequate soil drainage, plant high.

"High Planting" of Shrubs:

Till or break up the soil. For a single plant, dig a very shallow saucer and set plant with 1/3 to 1/2 the rootball above ground level, or plant on top of the existing soil. If roots of container-grown plants are thick and matted, or winding around in the container, gently loosen and spread the roots around in the saucer to enhance soil/root contact. For more than one bush, prepare the entire bed as directed below:

Backfill: To 2/3 native soil add 1/3 organic matter, lime if indicated, plus 1-2 Tablespoons of Superphosphate per plant, and mix thoroughly. Add no other fertilizer at planting time. Mound backfill above roots as shown in diagram.

Mulch: Cover with 3-4" of pine straw, mulch, pine bark chips or nuggets.

Water: Water well. High plantings dry out faster than traditional plantings but their survival chances are better. Pay close attention to watering for the first year or until plants are well established.

Planting Trees:

Recent research from the American Forestry Association has taught us that major changes are needed from the way we have traditionally planted trees. Instead of digging a hole, mark off a planting area at least 5 times the diameter of the planting ball. The bigger the better. With shovel or tiller, loosen and break up the soil in the area to a depth of 12 inches, adding lime if indicated.

Field-Grown trees or Balled and Burlapped Trees: DO NOT amend the soil. If the tree roots cannot live in our native soil, the tree cannot survive here.

Container-grown Plants: You may amend the soil with the same material that was in the container, as long as you mix it uniformly throughout the wide area, using no more than 1/3 amendment material to 2/3 native soil. Roots of container-grown plants are often "pot bound," with the roots circling around the inside of the container. Remove the plant from the container and gently tap the root system to remove the potting media and expose the rootsystem. Carefully fray and tease out the roots, loosening them so that they can be spread out in the planting saucer to obtain maximum soil/root contact.

In the center of the prepared area, dig a shallow saucer to set the tree. Set the root ball on solid ground, with the upper surface level or slightly above the existing soil level. See the diagram above. The tree should be planted at the same level it was grown in the nursery. Backfill around the root area, using water instead of your foot to settle the soil and prevent air pockets. Cover the entire area with 2-4" of mulch. Keep the tree watered well for the first year.

If you have any questions on the new way to plant trees, call the Cumberland County Cooperative Extension Service (910)484-7156.

Gardening Notes Index Page Return to Master Gardener Page
This information compiled by Cumberland County Master Gardeners.
This page was created on 4/20/98 using the Durham Master Gardener Homepage as a model. Our thanks to them and especially to Pauline Marx, Pam Reading and Eileen Lowenbach.
Revised on 05/07/98.