Green Scene

Rainy Season a Reminder to Fix Drainage, Percolation Problems

A community of plants can slow drainage on a slope or serve as a rain garden.
A community of plants can slow drainage on a slope or serve as a rain garden. (By Sandra Leavitt Lerner For The Washington Post)

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By Joel M. Lerner
Saturday, June 27, 2009

This rainy spring will be remembered as the season gardens didn't need irrigation. Grass was lush, shrubs and trees stayed wet, ponds and outdoor planters didn't require topping off. Other than weeding, it was a labor-free spring -- provided your property was well drained.

When the ground doesn't drain properly, it gets muddy. Nothing grows but bog plants, mold and algae. Even if you have a tiny plot of land or a single tree, the area must drain. Two types of control water are necessary to the health of your property: surface drainage and soil percolation.

Surface Drainage

Water in the basement is the most serious problem caused by poor surface drainage. In almost every situation, the culprit is the lack of surface water runoff or runoff in the wrong direction -- toward your basement instead of into an area that drains well.

Causes can include low spots hidden by planting beds or shrubs too close to foundations, or downspouts and gutters that don't carry storm water away from the house. Correcting the problem can be simple. Before considering solutions such as sump pumps, wall excavations, waterproof paints or sophisticated underground drainage systems, inspect for low spots near the foundation.

To fix the problem, channel storm water runoff. Generally, I suggest a downhill slope dropping three to six inches per 10-foot run. If a grade slopes down and away from your home, and continues slightly downhill, your basement will stay dry and the area should remain well-drained and usable for plantings or picnics. Basement walls or foundations for concrete slabs should have a grade that drains away from structures.

Do-it-yourselfers commonly overlook surface drainage when installing landscape features. Patios, walks and mounded beds can cut off existing grades, creating puddles that render these areas useless whenever there is precipitation.

Another common error is installing walks or patios perfectly level. This creates a situation that will hold water and promote the growth of fungi and algae. Paved surfaces should be laid so that they drop one inch over 10 feet. This is less than a 1 percent grade, and it will seem level to the eye and foot.

Even if water in the basement is not a problem, check the drainage patterns around your house during a storm to make sure that all water rolls away from the downspouts and walls. An ounce of prevention can save you gallons of problems and a barrel of mosquitoes.

If you see that water is not flowing away from your home, add soil to create a downhill slope along the walls. The fill should have a high percentage of clay in it and be low in rock, sand or compost. The soil within about two feet of the wall should have as little organic material -- composted leaves, wood chips or straw -- as possible. This "slope" of soil should direct water away from the structure, not help percolate it.

Build soil up against a masonry wall only, never against siding or wood. Draining against siding or wood requires removing soil five to 10 feet from the wall of your house and creating a downhill slope from the wall to a dish-shaped drainage channel, often called a swale. This will allow the water that once collected against the wall to flow down to the new swale.

Should your water problem be caused by circumstances beyond your control, such as underground springs, high water tables or creeks that have been piped underground, you may need subsurface pipes or sump pumps. But such residential drainage problems are rare.

If you are unable to resolve your problem by following common-sense steps, there are engineers, landscape architects and other professionals trained in diagnosing drainage issues.

Soil Percolation

Storm water doesn't always flow away from your property; it can be retained a little longer on site. This could be by choice, or because it's a boggy site with poor soil percolation, meaning water doesn't drain quickly enough.

To determine before planting if you have a problem with standing water, dig a hole, fill it with water and see how long it takes to drain. The length of time depends upon the size of the hole, but you'll know if you have poor drainage. I have dug holes, filled them and had water standing 24 hours later.

Most plants will not do well in hard, poorly drained soil. Improve the drainage by digging up to one-third compost into the native soil that is not allowing percolation. Dig it in as deeply as 12 inches and improve the soil over as wide an area as possible.

Use a rotary tiller to break up the dirt if the area is too large or the soil too hard to dig with a shovel. If you don't own a rotary tiller, you can rent one from an equipment rental company.

Before you improve with compost, test existing soil. A number of garden centers offer this service, as does your county Cooperative Extension Service. The proper test measures nitrogen, phosphorous, potassium and pH (acidity/alkalinity). Fix the site drainage now, but wait until September to add nutrients recommended as per the soil test results. You can plant, though, as soon as the drainage work is done.

One trend for improving soil percolation is a rain garden. Rain gardens are slight depressions in permeable areas of your garden that have been engineered to allow water to easily percolate into the soil. This has been a helpful innovation for neighbor relations because it keeps storm water on your own property. Look for more information on rain gardens and how to build them at http://www.chesapeakeecologycenter.org.

If you till a large area to help water percolate, it becomes a desirable root zone. Even though you might have planned to put one plant in that area, a group of plants would lend itself well to the larger cultivated space, as is practiced in the design and installation of rain gardens.

If you intend to plant the site, add organic material. This material, so critical to plant health, is broken down and used by the plants. It works for trees, shrubs and flowers anywhere, but especially on poorly drained sites.

Learn from the spring of 2009. Fix your surface runoff and soil percolation now. Then your basement will stay dry and your property and plants well-drained, even if future springs are as wet as this one has been.

Joel M. Lerner is president of Environmental Design in Capitol View Park, Md. E-mail or contact him through his Web site, http://www.gardenlerner.com.


© 2009 The Washington Post Company

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