Richard C. Bogren, Huffstickler, Kyle, Gill, Daniel J., Owings, Allen D.
News Release Distributed 11/19/10
By LSU AgCenter Horticulturists Dan Gill, Kyle Huffstickler and Allen Owings
Whether renovating an existing landscape or working on a new landscape, we need to remember that soil pH and proper preparation of landscape beds will be essential in determining the performance of your ornamental plants. A Louisiana landscape planned for long-term success includes these important considerations.
Optimum soil pH is critical for landscape success. Louisiana has soils that are somewhat variable in pH ranges. Ideally, a perfect soil pH for most ornamental plants in Louisiana is 5.5-6.5. Soil pH is a measurement of its acidity or alkalinity. A pH value of 7 is neutral while a pH value less than 7 is acid and a pH value greater than 7 is alkaline or basic. Soil pH is raised by using lime (normally dolomitic lime in landscape situations) and is lowered by using sulfur. Always adjust pH based on the results of a soil test.
Some plants in Louisiana landscapes and home gardens are classified as acid-loving. These plants do best with a soil pH slightly lower than other plants that we commonly grow. A soil pH in the 5.0-5.5 range is preferable for plants that require more acid growing conditions. Common examples are blueberries, camellias, sansanquas, dogwoods, azaleas, periwinkle, petunias and pansies. In turfgrass, centipede grass prefers acid soil, while St. Augustine grass prefers neutral to slightly alkaline soil.
The LSU AgCenter Soil Testing and Plant Analysis Lab can conduct soil testing for you. It will provide a report with information on soil pH and also the levels of many essential nutrients present in your soil. A routine test is $10. You can access information from the LSU AgCenter Soil Testing Lab at www.lsuagcenter.com/soillab.
Once you know your soil pH, you can move on to bed preparation. Several factors need to be carefully considered when you are developing beds for ornamental plants. Improving internal drainage should be the first priority. This can be accomplished by amending some of our existing soils, but more intensive work may be needed in more poorly drained soil types.
French drains can remove water from poorly drained areas by providing subsurface drainage. You can construct a French drain by first selecting an area lower than the landscape site. Dig a trench, fill it partially with gravel and lay pipes to carry water away from the planting site. Sometimes lawn areas benefit from French drains, and landscape beds may need French drains depending on the individual situation.
Raised beds are almost essential for successful landscape plant establishment if French drains or “pitcher’s mounds” are not used. A raised bed at least 6-8 inches deep can be enclosed with decorative bricks, concrete edging, landscape timbers, railroad ties or 4x4s. Chemically treated wood is safe for use around ornamental plants. A raised bed does not necessarily have to have a physical border on the edge. If properly prepared and well mulched when completed, the soil should hold in the bed and not wash away in heavy rainfall.
We recommend a “pitcher’s mound” or berm when planting an individual tree or shrub. This accomplishes the same thing as a raised bed, but it’s done for an individual plant. The berm should be 1 foot tall and needs to come out from the center gradually and slope down to the surrounding soil level.
If you’re 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 and causes a stagnant area beneath the new soil. It’s 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.
Soil preparation, drainage and pH are very important in landscape gardening success. Do not overlook this important factor.
Visit LaHouse in Baton Rouge to see sustainable landscape practices in action. The home and landscape resource center is near the intersection of Burbank Drive and Nicholson Drive (Louisiana Highway 30) in Baton Rouge, across the street from the LSU baseball stadium. For more information, go to www.lsuagcenter.com/lahouse and www.lsuagcenter.com/lyn.