Issue: August 30, 2008

It is difficult to keep weeds out

Question:

We have an acre of ground in the Las Cruces area and want to know what chemical we can use to treat the ground so that nothing will grow on it after we have pulled the weeds.

Jim L.

Answer:

Chemical applications for the purpose you have described are not recommended. Periodic treatments with a glyphosate based herbicide or other broad-spectrum herbicide(a product that kills both broad-leaf and grass weeds) are the only chemical approach. I consulted with Jamshid Ashigh, NMSU Extension Weed Specialist, who agreed that there are no products that could be recommended in this situation.

Jamshid did suggest use of soil covering materials to inhibit weed growth. In some situations black plastic will help, but in other circumstances it will cause additional problems. The black plastic will indeed inhibit growth of many weeds, but if there are other landscape plants nearby, their roots will grow under the plastic and in the future encounter problems. In garden areas, you can temporarily "solarize" the soil by heating the soil to a temperature that kills diseases and weed seeds near the surface by covering moistened soil with clear plastic (seal the edges of the plastic with boards, bricks, or soil to contain the "greenhouse effect" heat). It gets hotter under clear plastic than black plastic; however, the black plastic can also be used. This is a temporary measure as the plastic should be removed later to avoid impact on roots of landscape plants that would grow under the plastic.

You can also use weed barrier material that is porous and allows water and oxygen to penetrate the weed barrier.

This material would need to be covered with rock or other mulch to keep it in place, but due to its porous nature, it does not cause the problems that impermeable plastic causes for landscape plants. In time, you will find that soil and

weed seeds blown by the wind will accumulate above the landscape fabric and during the rainy season, many of these will begin growing. Some will be inhibited enough to be of little consequence, but some other weeds will need to be removed manually or chemically with herbicides again.

There are just no good products for the purpose you have mentioned. Even the long-persistence herbicides that remain active in the soil for long periods are more effective at inhibiting beneficial plant growth than at limiting weed growth. After their use, the only thing that will grow in the area is often the weeds.

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 and the NMSU Horticulture Publications page.

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

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