Water infrequently, longer for better lawn

Q&A With Sandy Feather

Editor's note: This is Part 2 of Sandy Feather's annual column on maintaining a healthy lawn.

Deep, infrequent watering during hot, dry weather is important to maintain a healthy lawn. Deep watering encourages the turf to develop a deeper, more extensive root system.

Conversely, frequent, shallow watering encourages a shallow root system. A shallow root system means a lawn is under drought stress when the top inch of soil dries out.

Use a sprinkler or an irrigation system to apply 1 inch of water weekly to your lawn when rain is minimal. This is best applied in one long, deep soaking session, rather than watering your lawn a little bit every day. Our clay soils can only absorb about one-half an inch of water an hour, so it should take two hours of watering to apply an inch of water.

To determine how long you have to run your sprinkler or irrigation system, take a flat-bottomed container such as a coffee can and mark off half-inch increments. Place the can or cans where it will be hit by the water, and time how long it takes to gather a half-inch of water. Then run your sprinkler twice as long. You may need to apply water even slower to steep slopes to avoid wasting water to runoff.

It is best to water in the morning. If you water during the heat of the day, too much water is lost to evaporation. If you water at night, the grass stays wet too long and may be more likely to have disease problems.

Allowing your lawn to go dormant during hot, dry weather is always an option. An otherwise healthy lawn can go about six weeks without rain; it will turn brown, but should recover when cooler temperatures and rain return.

A soil test will help you design a fertilization program that provides what your lawn needs for optimum health and growth. Inadequate or excessive fertilization can limit turf growth. It also will tell you what you have to do to get your soil pH (acidity or alkalinity) into the optimum range of 6.5 to 7.0 that most lawn grasses prefer. Soil test kits are available from your local Penn State Cooperative Extension office for a nominal fee.

Typically, late spring (mid- to late May), late summer (late August to mid-September) and late fall (mid-November) are the best times to apply fertilizer. Liming is best done in fall. Limestone moves through the soil very slowly and takes time to effect the desired change in pH. If your soil test reveals that your lawn needs 100 pounds or more of limestone per thousand square feet, break it into two applications, fall and spring.

You should also check your lawn for thatch. Older lawns often suffer from a deep thatch layer. Thatch is nothing more than a layer of organic matter between the soil surface and the crowns of the grass plants. Dig up a small square of turf so you can look at the soil profile. The thatch layer is easily visible.

Thatch is created when growing turfgrass sloughs off dead stems and roots. A thin layer of thatch -- a half-inch or less -- is desirable. It acts as a mulch, moderating soil temperature and maintaining soil moisture. More than that creates problems, though. A thick layer of thatch can keep water from reaching the soil, so your lawn is constantly drought-stressed. And that creates more thatch.

Thatch can also be a breeding ground for insect and disease problems. Even worse, if your lawn does develop a problem with white grubs (soil dwelling-insects that feed on turf roots), a thick thatch layer can make it very difficult to get an insecticide down to where the grubs are feeding.

The causes of thatch include:

• The variety of grasses in your lawn. Bluegrass and creeping red fescue are the worst thatch formers of the cool season lawn grasses.

• A soil pH lower than 6.5 immobilizes the microbes that break down thatch.

• Over-fertilizing your lawn.

• Frequent, shallow watering.

• Allowing grass to grow too tall, and then cutting it and not collecting the clippings.

A moderate layer of thatch (up to 1 inch) can be removed by dethatching your lawn with a power dethatcher. Dethatching is very stressful and should only be done in fall. You can rent dethatchers or hire a lawn service to do it for you. Run the dethatcher in one direction, and then go over you your lawn in the perpendicular direction. A good dethatching job should make you want to cry when you look at your lawn. Topdress the lawn with a thin layer (one-eighth to one-quarter inch) of good compost, then overseed with varieties of turfgrass that match your existing lawn to help it recover.

If you have over one inch of thatch, consider a total renovation, removing your existing lawn and starting over. The knives of most dethatchers will not go deep enough to get through the thatch and down to the soil, which is important for a good dethatching job.

If you do not have a thatch problem but the soil is compacted, rent a core aerator. Again, they are available from many tool rental shops, or you can hire a lawn service to do the aerating for you. Core aerators pull 3- or 4-inch plugs of soil and leave small holes behind. This helps aerate the soil (yes, roots need air!) and alleviate soil compaction. Fall is ideal for core aeration, but it can be done in the spring as well. If your lawn does not have a lot of activity on it, core aeration every three years or so will keep the soil aerated sufficiently. If all the neighborhood kids play in your yard, consider yearly core aeration in late fall to reduce soil compaction as much as possible.

You can break up the cores with a rake or allow them to stay on the lawn where they will break up during winter's freeze-thaw cycles. If they are creating too much of a muddy mess (when children and/or pets play on the lawn), you can rake them up and put them on the compost pile.

Topdressing with compost after core aeration is a good tool to slowly improve the quality of the soil under your lawn without tearing it up and starting over. A lawn is only as good as the underlying soil. A 6- to 8-inch base of topsoil that contains a moderate amount of organic matter is ideal, but few lawns have that luxury.

Send questions to Sandy Feather by e-mail at slf9@psu.edu or by regular mail c/o Penn State Cooperative Extension, 400 N. Lexington Ave., Pittsburgh 15208. First Published September 19, 2009 4:00 AM


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