Concrete debris can cause problems in the garden, but removing the concrete solves the problem.
Q. We recently had the concrete footings poured for an out building. I was disappointed to see that the crew cleaned the truck and tools on the very spot where I intend to grow plants. Besides the inconvenience of cleaning up hard concrete, do the chemicals in the concrete hurt the future plants? Even my civil engineering sons could not answer my question.
A. Concrete is made with Portland cement which composed of calcium oxide (largest proportion) and other minerals. Because of our arid climate in New Mexico, our soils naturally contain high levels of calcium and other minerals (not washed away by rainfall as in more humid regions). The excess calcium (and other minerals) in the soil can create problems for many garden plants.
Removal of the hardened concrete from the area intended for planting is the first step in avoiding problems. The larger pieces of concrete can be used in areas where rock mulch is used around native Southwestern plants or in areas not intended for planting. Native plants are adapted to growth in calcareous (high calcium content) soils and will not be harmed. The finer particles of the concrete that often results from washings from concrete equipment mixes with soil can be more of a problem, so spread it very thinly over areas where native plants will be grown, or put it where you do not intend to grow plants at all.
After you have cleaned the concrete and lime from the intended planting area, collect a soil sample and send it to a soil testing laboratory. Identify the plants you plan to grow there, lawn, or vegetables, or flowers. The soil testing laboratory will determine the level of soluble minerals in the soil and make recommendations based on the plants you intend to grow.
If you plan to grow vegetable or flowers that are grown over large parts of the country, you may be advised to add sulfur and organic matter to acidify the soil and improve its characteristics for the plants you will be growing. The laboratory will also advise you if nutrients important for plant growth need to be added as well. Autumn is a good time to submit soil samples so that you have time before planting in the spring to prepare your soil according to the recommendations.
Your local NMSU County Cooperative Extension Service office can provide guidance in collecting soil samples for soil testing and interpreting the soil test results. You can also get publications related to this online at the NMSU College of Agriculture, Consumer, and Environmental Sciences at http://aces.nmsu.edu/pubs/howto/howto.html. Specific publications to consider are Extension Guide A-114 "Test Your Soil", and Extension Guide A-122 "Soil Test Interpretations" You will receive useful interpretations from the NMSU Agronomist if you use the NMSU Soil and Water Testing Laboratory (information available from your local NMSU Extension Service office).
For more gardening information, visit the NMSU Extension publications World Wide Web site at http://aces.nmsu.edu/pubs/_h.
Send your gardening questions to:
Yard and Garden, Attn: Dr. Curtis Smith
NMSU Agricultural Science Center
1036 Miller Rd. SW
Los Lunas, NM 87031
Curtis W. Smith, Ph.D., is an Extension Horticulture Specialist with New Mexico State University's Cooperative Extension Service. NMSU and the U.S. Department of Agriculture cooperating.