Allen D. Owings, Trawick, Robert C., Bush, Edward W.
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, 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. Acid-loving plants are those that prefer a soil pH in the 5.0-5.5 range. Examples include bluberries, camellias, azaleas, centipedegrass, periwinkle, petunias and pansies.
Landscape Bed Preparation
Several factors need to be carefully considered when you are developing landscape beds for ornamental plants. Proper soil pH 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 feet by 4 feet 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. This 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.
Planting Annual and Perennial Flowers
A good way to begin planting annual and perennial flowers is to create islands of flowers in an open lawn, but because such beds are easily viewed from many sides, they often require high maintenance to keep them attractive.
Border plantings along a wall, fence, or hedge can soften the transition of landscape structures into the rest of the landscape or can create alleys of color. Rectangular beds lend themselves to a border planting where space is restrictive. When planting a perennial border against a hedge, fence or wall, leave a little space between it and its backdrop. This allows for better air circulation, more light penetration and ease of maintenance from the rear of the bed. Perennial borders often are 6 to 8 feet wide, allowing adequate space for at least a combination of six or more species, front to back, yielding a continual bloom.
To prevent turfgrass from growing into the perennial bed and becoming unsightly, use some form of broad edging or separating strip. Bricks laid flat, flagstone, bare ground or a heavy layer of mulch such as wood chips or bark will help keep out grass.
Annual and perennial flowers may be grouped according to color, intermixing plants that bloom at different intervals for a continual display. Plant height is a major consideration also. In border plantings, the tallest plants are usually placed towards the rear to serve as a backdrop with a few moved forward to prevent monotony in the design. In island plantings, they are placed toward the center. Fall-blooming perennials are usually the tallest, making them the best backdrop or accent plants. Most of the middle height perennial plants are summer bloomers and may occupy the majority of the middle space. Spring-blooming perennials are primarily short plants; place them toward the front. Emerging foliage and flowers of later blooming plants can help hide the fading foliage of earlier flowers. Narrow beds with excessively tall plants are usually not effective displays. Whether for borders or island beds, keep the width of a planting about twice the height of the tallest plant.
Planting Ground Covers
First, remove all existing unwanted vegetation such as lawn grass or weeds from the area. This could be done physically or you can use a herbicide such as glyphosate, but do a thorough job. It will be far more difficult to control problem weeds after the ground cover has been planted. Next, till the soil to loosen it. If you are working under a tree, use a turning fork to minimize damage to the tree’s roots, and avoid severing roots larger than an inch in diameter whenever possible.
After the soil is broken up, spread 2 inches of organic matter (compost, peat moss or rotted manure) over the surface and work it in. If necessary, 2-3 inches of additional blended soil mix (generally called topsoil or garden soil) may be added at this point. Finally, sprinkle 15-5-10 fertilizer at the rate of ½ cup per 30 square feet over the area, and thoroughly blend everything together. Now you are ready to plant.
Plant the ground cover at the proper spacing. This varies with the type chosen, so check with the staff at the nursery or your parish LSU AgCenter extension office. Planting at the closest recommended spacing will provide quicker coverage, but it will cost you more money. Generally, decide on a budget for the project, purchase as many plants as you can with the money and evenly space them in the area to be planted. If more are needed, purchase them as more funds become available and plant them among the existing plants.
Planting Shrubs and Trees
Fall is the ideal time to plant. For container-grown and ball and burlapped trees and shrubs, begin by digging a hole at least twice as wide and the same depth as the root-ball. After digging, ensure that about 1-2 inches of the root-ball is raised above the surrounding soil. For container grown plants, loosen with your hands or a knife any roots that have been matted while growing in the container. Also cut through any circling roots. During the planting procedure, return to the planting hole the same soil that was removed from the planting hole. Do not amend the backfill. Water in the plant to release any air pockets and use any remaining soil to build a berm around the hole to create a watering basin. If you have a ball and burlapped plant, be sure to untie or cut the burlap from the top one-third to one-half of the root ball.
One of the best management practices to improve or maintain optimum plant performance in a landscape is use of mulch. With mulches properly applied, many soil and plant related benefits can be realized. Add new mulch to landscape beds once or twice a year. Mulches are useful in the landscape to improve the appearance of bed areas, to modify the soil environment and to enhance plant growth. Organic and inorganic mulches can be used. Excellent organic mulches are pine bark, leaves, cypress mulch, grass clippings, compost and pine straw. Apply mulch one or twice annually. Be careful not to pile mulch around the base of the plant. This creates excessive water accumulation around the plant base and can cause root and stem rot problems. Mulch trees to a depth of 3 inches, shrubs to a depth of 2 inches and bedding plants/herbaceous perennials to a depth of 1 inch. Mulches also reduce soil moisture loss during dry periods, reduce soil temperature fluctuations, improves soil physical properties, suppresses weed growth and reduces soil erosion potential.