Soil pH, bed preparation important for landscaping

John Young, Gill, Daniel J., Owings, Allen D.  |  1/16/2009 8:14:48 PM

Sustainable Landscape News Distributed 01/16/09

By LSU AgCenter Horticulturists

Whether you’re renovating an existing landscape or developing a new one, keep in mind the importance of soil pH and proper bed preparation. These two factors are essential for the success of your ornamental plants.

A simple definition of soil pH is a measurement of acidity or alkalinity. A pH value of 7 is neutral. A pH value less than 7 is acid, and a pH value greater than 7 is alkaline or basic. The pH of the soil can be made more alkaline or basic by using lime (normally dolomitic lime in landscapes) or made more acidic by using sulfur. Always adjust pH based on the results of a soil test.

The pH range in Louisiana soils varies. Ideally, a perfect soil pH for most ornamental plants grown in Louisiana is 5.5-6.5. Some plants are classified as acid-loving, which do best with a soil pH slightly lower than other plants we commonly grow. These plants enjoy a soil pH in the 5.0-5.5 range. Common examples are blueberries, camellias, sansanquas, dogwoods, azaleas, centipedegrass, periwinkle, petunias and pansies.

Once you know your soil’s pH, you can begin bed preparation. Proper drainage is the first priority. You can provide this is by amending some existing soils, but more intensive work may be needed for our more poorly draining soils.

One solution is a French drain. This structure can remove water by means of subsurface drainage. Select a point lower than the landscape site for the water to drain toward. Dig a trench, fill it partially with gravel, and lay pipes, such as corrugated pipes with slits cut into them, to carry water away from the planting site. Lawns also may benefit from French drains.

Another solution is a raised bed. Make it at least 6-8 inches deep. You can enclose it with decorative bricks, concrete edging, landscape timbers, railroad ties or 4x4 lumber. Chemically treated wood is safe for use around ornamental plants.

A raised bed does not necessarily need to have a physical border. If properly prepared and well-mulched when completed, bed material should hold in the bed and not wash away in heavy rain.

When planting an individual tree or shrub, make a berm or “pitcher’s mound” instead of a raised bed. This formation accomplishes the same thing as a raised bed, but for a single plant. The berm should be 1 foot tall at the center and gradually slope to the surrounding soil level.

When making the berm over heavy clay soil, incorporate a 3-inch layer of new soil with the clay to form a transition layer. Otherwise, a sudden change in soil texture will disrupt the flow of water through the soil and create a stagnant area. It is highly unlikely that roots of a newly planted tree or shrub will move out of the planting hole without the transition layer.

To obtain a soil analysis, contact your parish LSU AgCenter extension agent. You will learn how to make a representative sample that the agent can send to the LSU AgCenter Soil Testing and Plant Analysis Lab in Baton Rouge for analysis of soil pH and several essential nutrient levels. Basic reports run about $7.

Come to LaHouse in Baton Rouge to see sustainable landscape practices in action. The home and landscape resource center is located near the intersection of Burbank Drive and Nicholson Drive (La. Highway 30) in Baton Rouge across the street from the new LSU baseball stadium. Go online to www.louisianahouse.org and www.lsuagcenter.com/lyn for more information.

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Contacts:
Dan Gill at (225) 578-2222 or dgill@agcenter.lsu.edu
Allen D. Owings at (985) 543-4125 or aowings@agcenter.lsu.edu
John Young at (225) 578-2415 or (225) 578-2222 or JoYoung@agcenter.lsu.edu
Editor: Mark Claesgens at (225) 578-2939 or mclaesgens@agcenter.lsu.edu

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