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Target nutrients and water

Several studies have shown that weeds are often better equipped for taking up mineral nutrients like nitrogen, phosphorus and potassium than are the crops with which they compete. Not only do the weeds produce root surface area at a faster rate (seed size), but also weeds typically attain 1.5 to 3 times higher concentrations of nutrients in their tissues. Consequently, highly available forms of nutrients like chemical fertilizers and rapidly decomposing organic fertilizers (e.g., fish emulsion) tend to favor weeds relative to crops. In contrast, the slow release of nutrients from green manures and compost tends to favor crops relative to the weeds. Particularly for long season crops, the slow release from organic materials may slow early top growth slightly but encourage a stronger root system and an overall healthier, more productive plant at harvest.

Although most of the mineral nutrition of the crop should come from soil organic matter built up by feeding the soil with green manure and compost, some heavy feeding crops like sweet corn and broccoli will yield better if given an additional nitrogen source (e.g., blood meal, composted chicken manure etc.) after they are well established. When applying such supplements, attempt to get the fertilizer close to the crop and work it in shallowly to avoid volatilization of ammonia. Avoid broadcasting the material widely where it will feed inter-row weeds before the crop can reach it.

Similarly, drip irrigation, which applies water next to the crop plants rather than sprinkling it over the whole garden, will favor the crop plants relative to the weeds. This is especially useful for managing weeds along the edges of beds where they usually receive less shade or root competition from the crop.