Soil Changes Can Damage Roots Of Trees

It won’t be long now. Soon the good earth will be lodged under our fingernails and ground into the knees of our jeans. We’ll be out clipping hedges, mowing lawns, planting seeds and enjoying every minute of it - right?

Some of us may even be toying with the idea of giving that old yard a new look. But before we begin any major reconstruction, we must take into consideration those stately old friends that grace our gardens - the trees.

We read and hear a lot about tree canopies - how they have to contend with disease, insects and mad pruners. But rarely do we read or hear about the massive root systems toiling beneath the earth.

It seems that, once covered with soil, tree roots are often forgotten and left to do their own thing - good or bad. On the positive side, there are huge stabilizing roots to hold the tree upright and in the ground and massive amounts of feeder roots to take in nutrients and water.

Unfortunately, they also can have some not-so-desirable traits. Because roots tend to swell as they mature, swollen shallow roots can heave out of the ground destroying lawn mowers and cracking sidewalks. Most roots have an unquenchable thirst. They will travel great distances looking for water.

No matter how they behave, the health of the root system can determine the health of the tree itself. So before digging, grading or dumping huge quantities of soil onto the ground around these fellows, we need to consider what’s living beneath our feet. These massive root systems need to be protected.

When we consider reconstruction in our yard, we must consider the location of the roots - how far are they from the tree and how deep? Most roots have established themselves where they will receive the proper amount of air, water and nutrients. If we are looking at raising the soil or creating raised planting beds, we must keep in mind that covering the roots with soil can suffocate them. Most major roots are incapable of moving up into the new soil.

The damage to the tree will depend on the type of tree, how much soil was used to cover the roots and the texture of the new soil - sandy or clayish, heavy soils being worse. Usually most trees will be adversely affected if covered with more than 6 inches of fill soil.

Lowering the grade can be just as destructive. Removing soil may scrape away and destroy feeder roots. Cutting large roots may weaken their ability to stabilize the tree.

Water tables can also be affected when grades are changed. If water rises and remains in the new soil, it can suffocate roots. If the water table drops when soil is removed, roots may die from lack of moisture.

And never pile soil up against the trunks of trees. Moisture may rot the protective bark, allowing disease and insects to invade the tree.

The damage to trees may manifest itself in any or all of the following ways: improper leaf size or development, stunting of the tree’s growth, thinning canopies and branches and twigs dying. This may develop over time or overnight.

Root pruning a few roots or covering roots with a few inches of soil should do very little harm to most trees. Before jumping into changing the terrain of your garden, consider the type of trees that will be affected and know where their other half is located.

On another note: I have received many requests for the phone number of Dick’s Tree Farm, a local distributor of the fast-growing willow I wrote about a couple of weeks ago. Here it is: (208) 772-5176.

Also, readers have called to ask where they can find the supertunia? The supertunia “Purple Wave” should be available at most garden centers in the spring. It can be purchased either as a potted plant or as seed. Other varieties can be ordered through Jackson & Perkins perennial catalog.

If you would like to learn everything you can about vegetable gardening, the WSU Master Gardeners will be hosting an informative lecture on vegetable gardening by Dave Swett, local commercial and hobby gardener extraordinaire. There will be two sessions Saturday, 10 a.m.-noon (“Organic Methods Vegetable Gardening”) and from 1-3 p.m. (“Vegetables from A to Z”).

Pre-registration is recommended, $5 per session, payable at the door; call 533-2048.