Pitfalls of Grass Clippings in a Vegetable Garden

Grass clippings can be a good mulch for vegetable gardens. They can suppress weeds, add nutrients to the soil as they decay and hold moisture and warmth near vegetable roots when weather is dry or cold -- all the things a good mulch can do. When applied properly, grass clippings are a virtually inexhaustible source of free mulch. Unfortunately, there are several pitfalls you can run into when using grass clippings from your own yard or someone else's.

Dry grass clippings thoroughly before spreading them in the vegetable garden. Wet, fresh clippings decay and ferment very quickly, which raises the temperature of the soil. If the grass mulch is too close to plant roots, it will burn and kill them. For an extra precaution, mix dried grass clippings with compost to lessen the heating effect.

Over-mulching is a big problem in many gardens. Grass clippings applied too thickly can trap moisture and grow fungus, bacteria and molds. All these things can kill or damage vegetables in the garden. Again, ensure grass clippings are dry before you apply them, and spread a layer no deeper than an inch or two.

Grass clippings are thin and fine and form a compact layer over time. Compaction can actually repel water and keep it from reaching the soil and vegetable roots. It can also keep oxygen from reaching the dirt. Rake out grass mulch and replace it with a new, loose layer every month or so to keep it aerated and to allow moisture to get through.

Many lawns are treated with "weed and feed" preparations of fertilizer and herbicides. While the herbicides don't harm the grass, they will kill the vegetables. Grass clippings that have been treated with herbicides should not be used in the garden. If you are determined to use these clippings, don't take clippings from treated grass until at least four weeks after the lawn is sprayed.