July 22, 2017

1 - Soil tests can help you prepare your soil to increase the chances of successful future gardens.

Yard and Garden July 22, 2017


I made to 2 bordered areas in my back yard. I need help! I have never been able to grow anything. I either water too much, or not enough. I plan to put in good soil. What is good soil? I also plan to put in a drip system. I would like to put in a vegetable garden in one area and a flower bed in the other. I would like to know what kind of dirt to start with. Can you advise, or get me started?

- Lou M.
Via e-mail


My first thought is to advise you to test your soil. Your local NMSU County Extension Service agent can give you information about collecting a soil sample and the address of a laboratory to test the soil. Testing the soil early gives you sufficient time to receive the results and add amendments and nutrients to the soil if needed. Your local Extension Service agent can help you interpret the test results if needed.

Gardeners new to the property may also want to consider conducting a bioassay test of the soil. This is a test to see if there are residual herbicides in the soil that could negatively influence the garden. Some herbicides can have an effect that persists for many years. To conduct this bioassay, collect some soil; make several mixtures of straight soil from the garden, 3 parts garden soil and 1 part potting soil, and 2 parts garden soil mixed with 2 parts potting soil. Mix the garden soil and potting soil well for each combination and then put each soil mixture into several small pots and plant some beans and corn in each pot. Water well, but do not make the soil soggy. If there is a broadleaf herbicide residue in the soil, the beans will grow poorly. If there is residue of a grass herbicide in the soil, the corn will grow poorly. If there is residue of a non-specific herbicide then both will grow poorly. It is unlikely that there will be a problem, but it is worth checking. The dilutions are to give you some idea of the concentration of any residue and to increase the chances for the beans and corn to grow.

Once you have determined that the soil has no herbicide residue and you have received the results from the soil test laboratory, you can make any adjustments recommended by the soil test lab. Our soils usually benefit from the addition of organic matter (compost). Both clay soils and sandy soils benefit from compost. The compost improves the soil structure, its water holding capacity, and its nutrient holding capacity. Your county agent can be of assistance again in determining what to add to the soil and how to do so.

You could excavate the old soil and replace it with purchased “garden soil” (usually compost mixed with sand or soil), but you can just purchase the compost and make your own mixture. At this time you can add any nutrients determined deficient by the laboratory test.

Preparing the soil in the autumn and allowing it to settle during the winter is good, but you can prepare the soil now and plant a garden for fall harvest. If necessary you can prepare the soil next spring.

Your county agent can also advise you as to plants that will do best in your county and your soils. Choosing the proper plants will greatly increase your chances of success. Extension offices and local garden clubs often offer classes to help new gardeners begin gardening. The information in these classes is valuable. For each site and plant species you need information about proper irrigation and these classes are a good place to determine how to irrigate properly for your soil and climate type.

Marisa Y. Thompson, PhD, is the Extension Horticulture Specialist, in the Department of Extension Plant Sciences at the New Mexico State University Los Lunas Agricultural Science Center, email: desertblooms@nmsu.edu, office: 505-865-7340, ext. 113.


For more gardening information, visit the NMSU Extension Horticulture page at Desert Blooms.

Send gardening questions to Southwest Yard and Garden - Attn: Dr. Marisa Thompson at desertblooms@nmsu.edu, or at the Desert Blooms Facebook page.

Please copy your County Extension Agent and indicate your county of residence when you submit your question!