Improving soil drainage walking across cessive drainage

Green Side Up

After walking across my yard and feeling as though I was walking on a wet sponge as a result of our recent rains, it occurred to me that I needed to know more about soil drainage. Even though there are some bog plants that will tolerate their roots standing in water, almost every plant that I have researched in the past has been designated as requiring “good drainage.” It has been said that good drainage may be the single most important factor in long range success in gardening and landscaping.

We gardeners tend to first think of the chemical aspects of the soil such as fertilizer and whether we need to add root stimulators or other growth enhancers. As important as these factors are, the physical characteristics of the soil may go further in determining the overall success of a gardening project.

These physical characteristics include such things as soil particle size which in turn influences optimum root growth. The balance of the quantity of air and water in the soil and the drainage or water retaining properties are other factors in attaining success. The combination of these factors is referred to as tilth.

Soils with good tilth are suitable for planting or growing crops whereas soils with poor tilth need amending before they make good garden soil. Soils with good tilth just “feel” good when you pick up a handful. They smell like good dirt, too. Managing soil tilth is a key factor in managing soil drainage. In general, large particles like sand drain quickly and leach nutrients away from the root zones whereas small particles that stick together like clay impede drainage and roots may stay wet.

In order to determine the adequacy of drainage in a given situation, it is possible to perform a “hole test.” Conduct the test by digging a hole approximately eight inches in diameter and about two feet deep. Fill the hole half full with water and note the time. If the water drains completely from the hole in fifteen minutes or less, the soil is exhibiting excessive drainage. This rapid drainage pulls air down into the soil and subjects the roots to drought-like conditions. If the water drains out in fifteen to thirty minutes, there is adequate drainage and no adjustments to the soil are necessary. If after thirty minutes or more the hole still contains water, a condition of poor drainage definitely exists.

Slow drainage is typical of clay soils, which are composed of closely packed small particles which allow the root zone to sit in water. This sets up anaerobic conditions that result in root rot and its associated bad smell. The addition of horticultural gypsum to dense soils helps to pull the clay particles together to form larger particles thus encouraging formation of more spaces. Expanded shale is also a good amendment for slow draining clay soils. Perhaps the best solution for both excessive and poor drainage conditions is the addition of a lot of organic material to the soil. Mature compost is an ideal amendment. Ideally, four or five inches of compost are worked into the top nine inches of the soil by some tilling method. The addition of organic material to soils will improve the water holding capability of fast draining soils as well as improving the draining ability of clay soils. Organic materials will also act as buffers in the soil and tend to bring acid and alkaline soils alike to a more nearly neutral pH. If raw materials such as sawdust, wood chips or incomplete compost are added to the soil, their decomposition will deplete the soil of available nitrogen. Plants will have to compete for the nitrogen, therefore, it is necessary to add a nitrogen fertilizer to the soil.

In extreme cases it may be necessary to resort to other practices to obtain adequate drainage. One method of doing this is to construct a French Drain. This involves digging a trench sloping away from the garden bed and putting down a layer of gravel in the bottom of the trench. Pipes with holes drilled into them are placed on top of the gravel and then covered with more gravel before reinstating the top soil.

Considering time, effort and cost professional services may be warranted.

Raised beds are an alternative method of correcting drainage problems. They give the gardener complete control of the soil quality. I am an advocate of raised beds because I feel they make watering, weeding, tilling, planting and all my other garden chores easier, and I like doing things the easy way.