Organic Gardener's Composting by Steve Solomon

_Grass clippings._ Along with kitchen garbage, grass clippings are the compostable material most available to the average homeowner. Even if you (wisely) don't compost all of your clippings (see sidebar), your foolish neighbors may bag theirs up for you to take away. If you mulch with grass clippings, make sure the neighbors aren't using "weed and feed" type fertilizers, or the clippings may cause the plants that are mulched to die. Traces of the those types of broadleaf herbicides allowed in "weed and feed" fertilizers, are thoroughly decomposed in the composting process.

It is not necessary to return every bit of organic matter to maintain a healthy lawn. Perhaps one-third to one-half the annual biomass production may be taken away and used for composting without seriously depleting the lawn's vigor--especially if one application of a quality fertilizer is given to the lawn each year. Probably the best time of year to remove clippings is during the spring while the grass is growing most rapidly. Once a clover/grass mix is established it is less necessary to use nitrogen fertilizers. In fact, high levels of soil nitrates reduces the clover's ability to fix atmospheric nitrogen. However, additions of other mineral nutrients like phosphorus, potassium, and especially calcium may still be necessary.

Lawn health is similar to garden health. Both depend on the presence of large enough quantities of organic material in the soil. This organic matter holds a massive reserve of nutrition built up over the years by the growing plants themselves. When, for reasons of momentary aesthetics, we bag up and remove clippings from our lawn, we prevent the grass from recycling its own fertility.

It was once mistakenly believed that unraked lawn clippings built up on the ground as unrotted thatch, promoting harmful insects and diseases. This is a half-truth. Lawns repeatedly fertilized with sulfur-based chemical fertilizers, especially ammonium sulfate and superphosphate, become so acid and thus so hostile to bacterial decomposition and soil animals that a thatch of unrotted clippings and dead sod can build up and thus promote disease and insect problems.