QUESTION: Our neighbor told us that he depends on earthworms to eliminate the thatch in his lawn. Have you ever heard of such a thing?
ANSWER: Earthworms are very important organisms that aid in the decomposition of plant litter, such as the thatch layer, and in recycling of nutrients. They help to break down and condition plant remnants in their gut. Their tunnels in the soil help oxygen and water to enter the soil more easily and their castings (waste) enrich it.
Thatch is a layer of living and dead roots, stems, and organic matter that accumulates at the soil surface. Thatch accumulates when the rate of decomposition is much lower that the rate of grass growth. The use of certain fertilizers or pesticides may encourage an accumulation of thatch by increasing turf growth and/or killing beneficial organisms, such as earthworms. Excessive thatch reduces the penetration of water and other materials, such as fertilizer. It also encourages shallow grass roots, which make turf more susceptible to stress and pests. A heavy buildup of thatch can easily impact on the overall aesthetic appeal of a home lawn.
Earthworms break apart thatch and pull organic matter into the soil. They also mix large amounts of soil into the thatch layer. This aids in a more rapid breakdown of the layer by increasing microbial activity and enhances its properties for growth of turfgrass.
Earthworms are sometimes viewed as pests because their burrows and castings create a roughened surface. Also, since earthworms are a preferred food for moles, pesticides are sometimes applied in an effort to remove food so that the moles will go elsewhere. There is no scientific evidence that the elimination of earthworms will reduce problems with moles. Earthworms make significant contributions to a fertile, healthy soil. Attempts to control them to reduce surface disruption can have severe consequences, especially in thatch build up.
QUESTION: We are confused. We read an article that says we should not collect the grass clippings when we mow because they help to fertilize the lawn. Won't they just add to the thatch layer?
ANSWER: Grass clippings contain valuable nutrients that can generate up to 25 percent of your lawn's total fertilizer needs. A hundred pounds of grass clippings can generate and recycle as much as three to four pounds of nitrogen, one-half to one pound of phosphorus, and two to three pounds of potassium back to the lawn. These are the three most important nutrients needed by lawns and commonly supplied in lawn fertilizers. The other good news is that grass clippings do not contribute to thatch since grass clippings are 75 to 85 percent water and decompose readily.
Mulching mowers are designed to recycle (re-cut) clippings underneath the mower housing resulting in clippings being cut into smaller pieces. These smaller pieces sift down into the lawn more readily than non-mulching mowers and reduce clipping debris on the lawn surface. Leaving grass clippings on the lawn saves time, energy and money, and reduces the amount of waste going into our landfills. By leaving your clippings on the lawn and allowing them to work their way back into the soil, you can realize these benefits and still maintain a beautiful, green lawn.
QUESTION: If we want to begin leaving the clippings on the lawn, should we mow it really short and then keep it mowed short?
ANSWER: No! Do not lower the mowing height of your lawnmower more than half an inch (one notch or setting on your rotary mower) per mowing or you will scalp your lawn causing browning of the grass. Normally this will not kill a lawn, but if your lawn has a thatch accumulation, the scalping or browning will extremely stress the lawn making it far more susceptible to damage from both insects and diseases. Do not remove more than one-third of the leaf blade with a single mowing. This time of the year, when grass is growing rapidly, you may have to mow it more frequently in order to prevent excessive clipping accumulation which can smother the grass and promote disease problems. Turf-type perennial ryegrasses should be mowed at 1 1/4 to 1 1/2 inches.
QUESTION: We have been told that we should mow our lawn in a different direction each time to make the grass grow better. Have you ever heard of this?
ANSWER: Don't get into the habit of following the same route each time you mow your lawn. This kind of routine can make a lawn less attractive, since lawn mower tracks tend to become fixed. Also, the grass will become harder to cut as it will begin to grow in one direction. High and low spots may become worse, and there may be a tendency for the lawn surface to develop a wavy appearance. Changing your pattern of mowing will give you a more uniform and neater lawn. Lawn clippings will be distributed better and there will be less packing of the soil if the wheels don't find the same tracks time after time.
One way to change the mowing pattern is to mow crosswise to the direction you used the last time. If this is impractical, then alter the pattern somehow so you don't go over the same tracks. It is better to follow a back and forth pattern rather than the around and around routine. Your lawn will look better and be healthier if you keep the mower sharp and adjusted to the proper cutting height.
EDITOR'S NOTE: For answers to local gardening questions, contact Master Gardener Rachel Gana at 642-8723 or e-mail her at firstname.lastname@example.org