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Coast Gardener

Good drainage helps plants grow
Coast Gardener Newspaper and Web Column - December 1, 2001

Unfortunately, the importance of good bed preparation is often neglected before plant material is placed in the landscape. Trees and shrubs are often placed in the ground without considering the soil type. This mistake will undoubtedly lead to plant death in many cases.

Different combinations of sand, silt and clay make up soil textures. Sand particles are the largest soil components that allow for good drainage. Clay particles are the smallest and often result in poor drainage. The proper soil type allows for good drainage and water retention at the same time. In addition, it provides adequate oxygen to the roots of the plants to encourage proper root development.

Before planting anything in your landscape, it is a good idea to see how well your soil drains. A simple test can be used to determine soil drainage. Use a large 46-ounce coffee can or similar container and remove the top and bottom. A 4-inch deep hole is dug and the can is pressed against the bottom of the hole. The soil should be firm enough so as the water will not leak around the sides of the can. After filling the can with water, wait about an hour and measure how far the water level dropped inside the container. If it dropped at least two inches, drainage is normal. If the water level dropped over five inches, the soil drains too much. If it doesn't seem to drain at all, drainage may be a problem for your plants.

If poor drainage is observed, gardeners have a couple of options. First, a French drain can be installed. This is actually a series of drains that are laid in a trench on top of gravel to carry away the water. Some people prefer planting in a raised bed. Raised beds should be at least 12 inches deep and may be enclosed with edging materials such as treated lumber or other landscaping accessories. Berms are actually large mounds of unenclosed soil that can really complement your landscape. Berms can range from one to several feet tall.

If you are planting on soil that offers poor drainage, try adding a 3-inch layer of soil amendments to give a transition layer between soil types. Sudden changes in soil texture will disrupt water flow through the soil. Choose amendment materials carefully. You want to form a well-balanced soil mixture in the planting hole so the roots can easily penetrate the surrounding soil.

Ideal soil consists of 15 percent air, 35 percent water and the rest solids. Sand, pine bark or leaf mold can be added to heavy clay soil. Two or three inches of leaf mold or pine bark is added per 6-inch hole depth. Sand can be added at the rate of four inches per 6-inch layer of clay soil.

Sandy soils can be amended to hold water by adding one or two inches of compost or peat moss per 6-inch depth.

Proper drainage is essential to the health of your plants. Many landscape plants simply cannot tolerate wet feet and poor soil conditions. By following a few simple procedures, your plants will grow happily in your landscape. Next week I will discuss the proper ways to transplant trees and shrubs in your landscape once the necessary steps have been taken to prepare the soil correctly.

These archived gardening columns were written by Chance McDavid, former Harrison County Extension Agent.