Soil ph, bed preparation important for landscaping

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 Vermilion Parish 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.  

The average soil pH for Vermilion Parish is an acid level around a pH of 5.8.  However, limestone driveways and the concrete slabs of homes will leach bases into the surrounding soil and this will often result in an alkaline value for homeowners.  Well water in Vermilion Parish also has a high pH often above 8.0.  The repeated use of high pH water over time will elevate soil pH in potted plants or areas that are not flushed well periodically with rainwater. 

Although pH is important in controlling the availability of nutrients in the soil, pH alone does not kill plants.  A much greater threat to the health of your plants is poor internal soil drainage.  We grow rice in Vermilion Parish because our soils have a clay hardpan that is ideal for impounding water.  However, most ornamental plants are not like rice.  They cannot tolerate flooded soils with low soil oxygen levels and will eventually succumb to root rot.  

One solution to improving drainage is the installation of  French drains. 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.

If water running off the roof keeps adjacent flower beds flooded you might consider installing gutters around the house. 

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, bring a pint of soil into the Vermilion Parish Extension Service Office at 1105 West Port Street in Abbeville.   The sample should be taken at a depth of 4 to 6 inches and should be a mixture from 10 to 15 locations.  It should be free from roots, leaves and other organic matter. From there the sample will be sent 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.

For more information about Soil Testing contact Stuart Gauthier, County Agent at the Vermilion Parish Extension Office at 898-4335 or come by and visit from 8:00 a.m. to 4:30 p.m., Monday through Friday at 1105 West Port Street in Abbeville.

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