Now that you’ve learned about plant competition for resources and the impact of herbicides, let’s return to our question from the last module: What is a weed?
Technically speaking, a weed is any plant growing where it is not wanted and in competition with cultivated plants. Cultivated plants are plants humans have selected to consume. Some indigenous and peasant communities don’t specifically cultivate plants- they might select certain plants for their consumption and encourage their growth, but don’t save their seeds to specifically grow them alone. When we call a plant a “weed”, it is a negative term, but it more broadly just refers to any plant not specifically cultivated. And to give a different perspective, these “weeds” or better, “wild plants”, are an integral part to the diets of small farmers around the world. In this module, you’ll explore more about how weeds fit into a larger agroecosytems understanding.
Weeds can reduce crop yields and crop quality through crop competition. Weeds compete with crops for nutrients, light and water. They can interfere with harvest, making it more labor-intensive and time-consuming. Weeds can also harbor diseases and pests. Weeds are adapted to disturbed habitats, so they can have an advantage in a cropping system over crop plants.
Weeds are usually considered to be detrimental, competing with the crop species and reducing yields. Weeds do often have these negative effects on crops, but it has been clearly shown that in many circumstances, weeds and other non-crop plants may benefit the crop community through their reactions on the environment. Weeds exert their beneficial influences in much the same way as cover crops and often fill the same ecological roles; with proper management based on an understanding of the mechanisms of weeds’ interactions, farmers can take advantage of their positive effects.
The well-known UC Santa Cruz Professor of agroecology, Steve Gliessman, says that “Weeds can protect the soil surface from erosion through root and foliar cover, take up nutrients that may otherwise be leached from the system, add organic matter to the soil, and selectively inhibit the more noxious species through allelopathy. Most of these benefits of weeds stem from the fact that ecologically weeds are pioneer species, invading open or disturbed habitats, and, through their reactions on the environment, initiate the process of succession toward more complex communities. Most crop communities, especially those composed of predominantly annual species, are simplified, disturbed habitats. Weeds are especially adapted to such conditions. When we gain an understanding of the ecological basis of the reactions of weeds on the crop environment, we can utilize their interference in ways that reduce the need for inputs from outside the crop community.” (Gliessman, 2006)
Finally, wild plants have an important place in most traditional diets. Wild plants can have increased antioxidant levels compared to cultivated greens, and many medicinal plants can be found growing in the wild. In many traditional farming systems, wild greens or “weeds” play an important part of the system and the culinary traditions that accompany these farming systems.
By pausing and learning about the plants growing in our farming systems, it’s possible to learn to appreciate them. They can be food, medicine, used as animal fodder, or composted.
It’s also important to note that weeds can gain the upper edge when a site is tilled frequently, putting a natural system off balance. Farming practices that mimic nature, like using less or no tillage, it is possible to almost eliminate weeds over time, so that a weed seed bank doesn’t build up in your soil.
“If it weren’t for weeds, the world would have lost more topsoil than it has to date, and humankind might have suffered mass starvation by now. Why? Because the plants we call weeds do a vital job in ecosystems: they quickly establish in, protect, and restore soil that has been left exposed by natural and human-caused disturbances. ” Read more…
Case Study: Milpas and Quelites
Read the following short selection about quelites, and their role in the Milpa farming systems of Mexico and Central America. Please read the excerpt between second paragraph page 157 and the end of the first paragraph page 159:Read Excerpt: Food's Frontier
Traditional Cuisine and “Weeds”
Many traditional cuisines have dishes that use wild greens. Here are a few examples.
Kenyan Sukuma Wiki
Wild Greens for Cretan/Greek Spanakopita
Lomo de cerdo con verdolagas (Purslane)
Check out this great resource, provided to us by Pamela Sherman, a 2017 MESA Applied Agroecology Course participant!Relationship with Weeds : Some Plant Use Profiles and Ecological Management
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Gliessman, Stephen R. Agroecology: the ecology of sustainable food systems. CRC Press, 2006.