Daniel Gill, Bogren, Richard C. | 9/9/2009 9:39:41 PM
By Dan Gill
LSU AgCenter Horticulturist
Fall is a prime planting season in Louisiana. Cool-season flowering bedding plants and cool-season vegetables are planted from now through February, 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 air (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.
There are many different kinds of soils in Louisiana. Knowing the characteristics of the soil in your garden is necessary to understanding how you may need to modify the soil 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 parish LSU AgCenter Extension office. Your county 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’s soil testing laboratory in Baton Rouge for $7. Kits to submit soil samples for analysis are available from your local extension office.
The test will tell you the texture, fertility level and pH. You should get back your test results in two to three weeks – just in time to prepare beds for our prime planting season. If you need to, you can contact your local county agent to help you understand the results and decide what needs to be done.
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 (various 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 at least 8 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 two to four 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 bagged from your local nursery. Other suitable choices of organic matter include aged manure (available from local stables or bagged at nurseries), peat moss, soil conditioner or finely ground composted pine bark.
If a soil test indicates that your soil is alkaline (a pH above 7), sulfur, copperas (ferrous sulfate) 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 the 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 moderate to high, generally choose an all purpose fertilizer with about a 3:1:2 or 4:1:2 ratio, such as 15-5-10, 16-4-8 or something similar. Appropriate organic fertilizers could also be used. Remember, a soil test can help you decide what amendments need to be added to your soil.
Finally, thoroughly blend all of the amendments you have applied into the soil of the bed. A garden tiller 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 it was before preparation. This is desirable as it will help improve drainage.
I won’t deny that this is hard work. But the results you get in healthy, vigorous plants make it well worth the effort.
Get It Growing is a weekly feature on home lawn and garden topics prepared by experts in the LSU AgCenter. For more information on such topics, contact your parish LSU AgCenter Extension office or visit our Web site at www.lsuagcenter.com. A wide range of publications and a variety of other resources are available.