Soil Test for Fall Planting

(News article for August 28, 2020)

Fall is a good time to plant most trees and shrubs in Louisiana. While people get excited about buying plants in the spring, planting in the fall gives plants more time to establish their root systems before hot weather hits and water demand is greatest.

Most plants purchased at local nurseries will be containerized. With enough coddling, containerized plants can be planted at any time of year, but planting in the fall is ideal for most types of trees and shrubs.

There are exceptions to the planting-containerized-trees-and-shrubs-in-the-fall-is-best rule. It’s advised that citrus trees be planted in January or February and that fig trees, which are more cold-sensitive when young, be planted just before bud break in the late winter.

Sometimes, when people order plants, these come in bare-root form. These should be received and planted only while they are dormant. So, you’ll need to wait a little longer to plant these than you will to plant containerized plants.

Large landscape plants are occasionally purchased in balled-and-burlapped (B&B) form. You have more flexibility with respect to planting time with these than with bare-root plants, but the dormant period is likewise recommended.

Fall will be arriving soon. It’s a good idea to soil test before making large investments of time and money in tree and shrub plantings. Once they’re planted, it’s more difficult to adjust soil pH (acidity or alkalinity) and phosphorus levels, in particular. (Some plant nutrients are more mobile in the soil than others.)

If soil pH needs to be adjusted, it’s best to add lime (to raise pH) or sulfur (to reduce pH) at least several months before planting. It takes time for soil pH to change.

When soil testing an area, be sure to get multiple (10 or so) sub-samples within that area. Mix these together so that you have at least a pint of soil. For home tree and shrub plantings, sampling to a depth of about 6 inches deep is reasonable.

There are a couple of ways to get a soil sample to the LSU AgCenter’s Soil Testing and Plant Analysis Laboratory. One way is to use one of the flat rate mailing boxes that are available at various locations. (If you plan to pick up a box at an AgCenter office at this time, call first to make sure you can get one. Offices are closed to the public at the time of writing.) When these are used, a $7 charge for postage is tacked on to the $11-per-sample cost. Another option is just to use the soil testing form on the Soil Testing and Plant Analysis Laboratory’s website and mail samples using your own packaging.

When you receive your soil test report, you’re welcome to contact me (or the horticulture agent for your parish) for assistance in interpreting it. If nothing else, be sure to look at the fact sheet that comes with your report or for which a web link is provided on the report. The accompanying fact sheet often provides information that is very important for interpreting the results.

Let me know if you have questions.

Contact Mary Helen Ferguson.


Combine soil from multiple spots in each sampled area. (Photo by M.H. Ferguson)

9/9/2020 8:08:34 PM
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