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The Importance of Cover Crops
Rafael A. Vega
Doctor of Plant Medicine Student, IPM Florida
University of Florida, Entomology and Nematology
Weeds are the biggest challenge to overcome in an organic setting. Close to 60% of all pesticides are herbicides that are readily available to agronomists in a conventional setting. To overcome such overwhelming odds organic farmers need to use a combination of tactics to manage weeds. The best way to beat weeds is to eliminate or limit sunlight for active growth.
Many people believe that by actively pulling weeds you can eliminate future weeds from plaguing their gardens. While pulling weeds is certainly helpful, it can also damage desired roots from your crop. Most importantly, there is an endless supply of dormant weed seeds waiting to germinate as soon as conditions are favorable (light exposure, bare ground, irrigation). Using a hoe to cut above ground weed growth will slow down the weed’s photosynthesizing capabilities and leave your crops roots intact. It is wise to pull weeds in rows and borders that don’t threaten your crop.
Probably the most effective way at limiting weeds is with competition using cover crops and desired crops. A healthy crop will limit sunlight to weeds. Cover Crops are used to create a rapid canopy cover and prevent weed seeds from germinating or surviving. There are many cover crops available and many are much less expensive than typical vegetable seeds or seedlings.
Many people think that native weeds are just as effective as a cover crop. Unfortunately, most weeds are weeds because of their rapid growth, high seed dispersal rate and persistent nature. What this means is that most weeds mine the soil of nutrients (nitrogen, phosphorous and potassium) to store in their rhizomes or stolons and put out copious amounts of seeds that may lay dormant for many years in your plot and throughout the garden. The benefit in cover crops is their ability to quickly out-compete weeds with beneficial impact on the soil and provide green manure for your garden. Many varieties also add nitrogen to your soil. Their slower reproductive rate makes it much easier to manage. The biggest benefit is that they are low maintenance. Most varieties can be planted and left alone.
So if you are planning to be away from your plot, it’s a good idea to plant a cover crop to help your soil and help your neighbor’s plots by not exposing them to your weed seeds. When planting cover crop seeds it is usually a good idea to seed heavily to allow for complete coverage of your desired area.
There are many cover crops available. For summer, a combination of buckwheat and Iron/clay cow peas is a great cover crop. Buckwheat germinates quickly, out-competes Bahia and Bermuda grass as well as most other weeds, helps add organic matter, attracts beneficial insects, and increases soil structure. The cow pea helps add nitrogen to your soil. Some buckwheat seed is available in the shed at the garden. Cow pea is not currently (as of 11/06/09) available at Alachua Feed, but can be purchased at other gardening stores. Other summer cover crops include Sorghum-sudan grass, sun hemp and velvetbean. Legumes are always helpful, but make sure they have nodules on their roots because they may not be fixing nitrogen.
Good resources for cover crops: