I often get asked about using grass clippings as a mulch for plants in the garden. On the surface this would seem like a great way to utilize the clippings in a way that does not add to our landfills or pollute our storm sewer or waterway systems.
However, there are some real "Watch Outs" if using lawn grass clippings for mulch. To start out, lets review why we mulch in the first place. There are a couple or very important functions that a good mulch layer will provide to the gardener.
- Mulch, applied correctly, conserves moisture in the soil making rainfall and watering practices last a lot longer
- If mulch is applied at a depth of at least 3 inches in beds and around trees it acts to prevent weed growth by shading the weed seeds so that they don't germinate
- Mulch acts as an insulator for the soil, warming it in cold weather and cooling it when its hot. This moderating effect makes plants, especially shallow rooted plants grow more vigorously
- Esthetically, mulch adds a common, consistent, and neutral background to plants and trees which is pleasing to view
- As it decays, organic mulch such as pine bark, shredded hardwood, and other mulches (Not stone) add organic materials to the soil structure, enriching the soil.
Now back to grass clippings. The first thing about grass clipping that I always point out is that you should not have any. Today's lawn mowers nearly all offer a mulching attachment which cuts grass blades multiple times leaving a finely chopped clipping which sifts easily back to the soil surface and which does not need to be picked up. Simple. If you follow the rules about "mowing high" and taking no more than 1/3 of the grass height off at each mowing, and combine these practices with a mulching mower you should never have grass clippings to pick up.
However, there are those of us who bend these rules a little, and who end up with piles of carefully raked grass clippings which most towns now will not pick up as regular garbage. Many people would like to use these clippings as mulch for gardens. There are some compelling reasons not to do this.
- Contamination - Weed killers and fertilizers applied to lawns can make mulching with grass clippings a roll of the dice for your other plants. If you applied weed killer within the last few weeks the residual contaminants could damage plants where the clippings are applied as mulch. Further, some insecticides applied to lawns are not to be applied to vegetable plants, providing another contamination problem
- Compaction - At best, grass clippings used as mulch will compact so much after they are applied that they would be inefficient as a mulch. If you apply 3-4 inches of fresh grass clippings to your beds, by the time it dried and settled it would yield less than an inch of mulching benefit
- Odor - Grass clippings applied as mulch will begin to decompose very rapidly, and during that decomposition they can have a very unpleasant odor, not what you want conflicting with your roses and gardenias in the garden
- Heat of Decomposition - applied deeply enough to be a viable mulch, grass clippings release heat when they decompose which can damage plant roots and stems, and disrupt the temperature of the soil, leading to poor plant vigor and disease development
- Appearance - Mulched grass clippings turn a light brownish yellow and as such don't add much to the visual appeal to your garden.
The practice of mulching is a very valuable addition to your gardening experience. However, using grass clippings as mulch may do more harm than good based on the observations above. So, what should you do with grass clippings if you still have them around. Try composting them with other garden waste. Clippings need special care when incorporating into a compost pile, but they can be successfully added if you follow a few rules. There is plenty of information on composting at the University of Illinois site and other sites online.
The best way to deal with grass clippings is not to have them at all. Follow the rules of 1/3 of the grass height, and use a mulching blade or mower and you should not have to deal with these piles of grass at all.
SG
