August 17, 2013

1 - The monsoon rains cause rapid development of weeds that require persistent management in New Mexico gardens.

Yard and Garden August 17, 2013


Until the rains started this year I had almost no weeds in my yard and garden. Then weeds appeared suddenly after the rains. I guess that is no surprise, but now I cannot seem to get rid of them. I have been digging the weeds up and chopping them with the hoe at least once a week, but they reappear almost immediately. What can I do?


In New Mexico we have an advantage over other gardeners in that our dry environment reduces weed growth. This year was extremely dry, so there were very few weeds. Weeds could only develop in areas where plants were irrigated. Gardeners who employed drip irrigation had only small areas in which to manage the weeds. However, potential weed problems were waiting for the monsoon rains as were New Mexico gardeners.

Once the rains began, and continued on a frequent basis the perennial weeds waiting below the soil surface as well as weed seeds began to grow. The perennials could develop quickly because they had established root systems to quickly provide water to the developing shoots. Digging and hoeing help remove them, but in the case of many of our perennial weeds, such as silver-leaf nightshade and bind weed, they redevelop rapidly from the extensive perennial root systems. Appropriate herbicides may help somewhat, but they will need to be applied several times and used in strict accordance with the label directions. Manual removal is also effective, but as in the case of the herbicides repeated treatment will be necessary. If you choose to use herbicides, your local NMSU County Extension agent can help you identify the weeds and appropriate chemicals. Successful manual removal does not require that you identify the weeds, but will help you distinguish between desired plants and weeds. Frequent and persistent management of perennial weeds can weaken their root system and reduce the problems they cause. In time, you may eliminate or greatly reduce these weeds in your garden.

Annual weeds also develop quickly after the rains. They must grow from seeds, but as weeds they are very capable of developing quickly. They may also be managed by herbicides, but this again requires proper identification to find an appropriate chemical and, as before, the instructions must be understood and followed. Manual removal of annual weeds is also a very effective management technique. Since annual weeds do not have established root systems, if they are completely removed by hoeing or digging, they will not reestablish. However, there are great numbers of annual weed seeds waiting in the soil. They do not all germinate at the same time, so new weeds will continue to develop as long as the moisture persists. Managing annual weeds quickly so that they cannot form seeds helps reduce potential problems in the future, but there will be seed remaining in the soil for years. Many weeds can form seeds within a week or two from the time the seeds germinate, so frequent removal is important. Another nasty characteristic of annual weed seeds is that they can remain dormant in the soil for many years, especially if they are deeply buried. When hoeing weeds, you often bring deeply buried, dormant seeds to the surface where they can germinate. Chopping deeply to remove these weeds can result in more weeds, but specialized hoes that cut the roots just below the soil without turning the soil over can help you avoid this problem. Such hoes are called scuffle hoes, hula hoes, or stirrup hoes. Such hoes are very helpful in managing weeds manually in our gardens.

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:, office: 505-865-7340, ext. 113.


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

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