Optimum soil pH is critical for success with your landscape plants. The ideal soil pH for most ornamental plants growing in Louisiana is 5.5-6.5. A simple definition of soil pH is a measurement of the acidity or alkalinity. A pH value of 7 is neutral, a pH value less than 7 is acidic, and a pH value greater than 7 is alkaline or basic. Soil pH is raised by using lime (normally dolomite lime) and is lowered by using sulfur. Always adjust pH based on the results of a soil test. Acid-loving plants are those that prefer a soil pH in the 5.0-5.5 range. Examples include blueberries, camellias, azaleas, centipedegrass, periwinkle, petunias and pansies.
Several factors need to be considered carefully when you develop landscape beds for ornamental plants. Proper soil pH, as previously mentioned, and internal drainage are very important. This can be accomplished by amending some of our existing soils, but more intensive work may be needed in our more poorly drained soil types.
French drains remove water by providing 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 to carry water away from the planting site.
Raised beds are almost essential for successful landscape plant establishment and resulting growth (if French drains or “pitcher’s mounds” are not used). Make a raised bed at least 12 inches deep. A raised bed can be enclosed with decorative bricks, concrete edging, landscape timbers, railroad ties or 4-inch-by-4-inch wood. Chemically treated wood is safe for use around ornamental plants.
A “pitcher’s mound” or berm is recommended when planting an individual tree or shrub. A berm accomplishes the same thing as a raised bed, but it’s done on an individual basis. The berm should be 1 foot tall and needs to come out from the center gradually and slope down to the surrounding soil level. When planting directly in a heavy clay soil, incorporate a 3-inch layer of new soil to form a transition layer between the existing soil and any soil that is added. A sudden change in soil texture disrupts the flow of water through the soil. This causes a stagnant area beneath the new soil. It is highly likely that roots of a newly planted tree or shrub will not move out of the planting hole if you don’t follow proper planting procedures.