Ways to Drain Soil

This continues last week’s article about soil drainage. It’s all fine and dandy to talk about soil drainage, but how in the world do you do it?

  • Topic: Soil
  • Author: Cindy Bellinger
  • Keywords: soil, soil drainage, berming, trench, pipe
  • Date: November 2005

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This continues last week’s article about soil drainage. It’s all fine and dandy to talk about soil drainage, but how in the world do you do it? How can you rearrange low-lying places?

One solution to tough drainage problems is berming planting areas. That is, making and planting on a raised hill or mound so water naturally runs off. If you’re not starting from scratch, this will require uprooting and transplanting flowers and shrubs. It also means bringing in some fill or top soil to make the berm. The size of hill all depends on your garden space.

For instance, a new area in the Chicago Botanical Garden that was raised and walled for over a mile along a busy highway reduced noise by 50 percent.

Another solution for areas prone to standing water is to install a drain line—a perforated 3-inch plastic drainpipe inbedded 12 to 15 inches.

  1. Find a spot below the level of the garden where water drains away.
  2. Measure the distance from the lowest point in the garden to this area. Then buy enough perforated 3-inch diameter PVC pipe to cover that distance.
  3. Dig a trench sloping downhill between the two points. Try for a drop of about 1 inch for every 10 feet of ground.
  4. Line the trench with about 3 inches of gravel. Lay the pipe on the gravel and cover with agricultural fabric to prevent soil from clogging the perforations.
  5. Add 6 more inches of gravel over the pipe; cover with soil.

If the lowest level also doesn’t have a natural drainage area, you might need to connect two pipes to make this work.

A Word of Caution

If during construction, excavating or landscaping, the slope or grade of a surface may be changed. Only a few feet of extra soil added to the surface will adversely affect trees. The added soil interferes with the exchange of gases, particularly oxygen, between the roots of trees and the air above the soil surface.

Protect older established trees when carrying out a major grade change. The construction of large “wells” which coincide with the drip line (the furthest extent of the branches) will maintain the existing grade around these trees. Similarly, if soil is to be removed, retain the soil around existing trees through the use of a retaining wall extending to the drip line.

Water is essential for plant growth, but too much can result in the death of plants. Another way to work with soil drainage, is to consider the soil and water needs of plants you’re putting into your garden. More on that another time.