Richard Bogren, Gill, Daniel J.
By Dan Gill
LSU AgCenter Horticulturist
(10/13/17) Fall is a prime planting season in Louisiana. Cool-season bedding plants will be planted from now through early December, and November through February is the best time to plant hardy shrubs, ground covers and perennials in the landscape. How well you prepare the soil prior to planting has an enormous effect on the health and growth of your plants.
Gardeners often put too little effort into learning about their soil and what is needed for proper bed preparation. Soil is the primary source of water and nutrients for plants and must also provide sufficient oxygen to the root system. A gardener’s job is to make sure, through proper bed preparation, that the soil provides what plants need to be healthy and strong.
Louisiana has many kinds of soils. Knowing the characteristics of the soil in your gardens is necessary to understanding how you may need to modify it to benefit the plants you intend to grow.
You can learn about your soil by talking to individuals knowledgeable about the soils in your area. A great place to start is your local parish LSU AgCenter office, where the agent will be able to familiarize you with the characteristics of the soil in your area.
You can also have your soil tested by the LSU AgCenter soil testing laboratory in Baton Rouge for $10 per sample. Mailing boxes and forms to submit soil samples for analysis are available from your local AgCenter office. Or you can go online and visit the LSU AgCenter Soil Testing and Plant Analysis Laboratory at www.lsuagcenter.com/stpal. There you will find information on how to take and submit a soil sample, download forms and see the answers to frequently asked questions.
The test will tell you the texture, fertility levels and pH of your soil. The analysis will include nutrient levels in the soil and fertilizer recommendations based on what you intend to grow. If needed, lime recommendations are also included.
You should get your test results in two to three weeks — just in time to prepare beds for our prime planting season. If needed, you can contact your local AgCenter agent to help you understand the results and decide what needs to be done.
You will also have the soil test results on hand when it comes to spring fertilizing season next year. Soil test results will help you choose the best fertilizers for your soil fertility level.
Shrubs, ground covers, vegetables, annuals and perennials should always be planted into well prepared beds. Trees are generally planted into individual planting holes, and the soil used to fill in around their roots should not be amended. The soil of beds, however, is usually improved in some way with the addition of amendments. Soil amendments are materials blended with the soil to enhance the growth of plants to be planted in the bed. Here are the basic steps in preparing a bed.
First, do a thorough job of removing unwanted vegetation in the bed. This might mean taking up existing turf to create a new bed or just cleaning out weeds that have grown up in an existing bed. Weeds or turf grass may be removed physically or killed with a herbicide. If you are removing weeds by hand, use a shovel or trowel to get out all of the roots, rhizomes and bulbs. As an alternative, you may spray and kill the weeds with a systemic herbicide, such as glyphosate (Killzall, Roundup, Eraser and other brands), that will not leave a residue in the soil.
When the weeds or turf have been dealt with, turn the soil over to a depth of 8 to 10 inches using a shovel, spade or garden fork, and break up the large clods.
Next, spread any desired soil amendments over the turned soil. You will almost always want to add 2 to 4 inches of organic matter. I think homemade compost is the best, and every gardener should have a compost pile. If you can’t make your own, you can purchase compost from local companies or city departments that produce it or get in bags from your local nursery. Other suitable choices of organic matter include aged manure — available from local stables or in bags at nurseries — peat moss or finely ground composted pine bark.
If a soil test indicates your soil is alkaline (a pH above 7), sulfur, copperas or aluminum sulfate may be applied to make it more acid. This is especially important if you intend to plant acid loving plants. If your soil is too acid (a pH below 5.5), lime or dolomitic lime may be applied to raise the pH and provide essential nutrients such as calcium and magnesium.
The fertility level of the soil may be improved with addition of fertilizer. If your soil is low in phosphorus and potassium, generally choose an all-purpose fertilizer with about a 1:1:1 ratio such as 8-8-8 or 13-13-13. If phosphorus and potassium levels are adequate to high, generally choose an all-purpose fertilizer with about a 3:1:2 ratio, such as 15-5-10. Appropriate organic fertilizers could also be used. Remember, a soil test can help you decide which amendments need to be added to your soil.
Finally, thoroughly blend all the amendments you have applied into the soil of the bed. A rototiller is great for this step, but it can also be done by hand. Rake the bed smooth and shape the sides, and you’re ready to plant. When you finish, you will find that the bed is several inches higher than is was before preparation. This is desirable because it will help improve drainage.
This is hard work, but the results you get in healthy, vigorous plants — whether they are vegetables, flowers, shrubs or ground covers — make it well worth the effort.
Samples of soil 6 inches deep from several locations in a garden or lawn can be tested to provide information on soil pH and fertility. Test results come with recommendations based on the type of plants you intend to grow. LSU AgCenter file photo by Tom Koske
Bulk landscape soil may contain bark, aged tree debris, rice hulls, wood ash and other organic materials. LSU AgCenter file photo by Allen Owings