Garden Design - Water and Drainage II

What to do when you have poor drainage

Poorly drained soil doesn’t mean that you can’t grow a good garden. It only means that you have to pay special attention to drainage and select appropriate plants as you plan your garden. There are many options for working with soil that is persistently or periodically wet.

1.       Level out low-lying areas? Fill them with good quality topsoil. Fill small areas by hand or rent a skid steer loader, such as a Bobcat, to fill and grade larger areas.

2.       Amend tight clay soil: Spread a 4 to 6-inch layer of organic matter and rototill or dig it in 12 inches deep.

3.       Use raised beds: to grow plants that need more soil depth than your site provides. We’ll be discussing on how to build a raised bed in future articles.

4.       Contour the site: with berms and swales. A berm is a low, rolling hill that sits above the surrounding soil level and channels the water’s flow. A swale is an open grassy drainage ditch, with sloping sides, that carries away excess water. Use berms and swales together in areas where standing water is a frequent problem. Building berms and swales requires the use of a skid steer loader, backhoe or bulldozer.

5.       Create a dry creek bed lined with rock. A dry creek bed functions like a swale, carrying away excess water. Ornamental grasses, ferns and other plants with well-defined textures look smashing when massed along a dry creek bed.

6.       Make a bog garden in an area that stays permanently damp. In addition to accommodating interesting plans such as willows, sedge and Japanese iris, bog gardens attract aquatic loving wildlife such as dragonflies, frogs and turtles.

7.       Install a French drain: This is an underground drainage system made of 4-inch wide perforated pipe which is laid in a bed of gravel 2 feet below the surface. Because water flows downhill, you will need an outlet area such as a drainage ditch that is lower than the area that needs to be drained. A 4-inch wide pipe will drain 25 square feet of area on either side of it.

What are the effects of Poor Drainage?

1.       Soil stays cold and wet in the spring, which delays planting and reduces seed germination

2.       Plants drown due to lack of oxygen in the soil

3.       Plants develop  shallow roots

4.       Roots and crowns rot during the winter

How to test for Drainage

Run this simple test to see how your soil drains. Dig a hole 18 to 24 inches across and the same depth. Fill the hole with water. If water disappears from the hole in 10 minutes or less, you have sandy soil with fast drainage. If the water takes one hour or more to drain away, you have clay soil or an impermeable layer of compacted soil beneath the soil surface (hardpan), and the soil is poorly drained. There are many acceptable variations between these two extremes.

Stay tuned as we continue our series on Designing your site and overcoming or correcting obstacles that may stand in the way of your having the Garden of your Dreams.