Question: A few years ago we put in a beautiful sod lawn, but now it is looking a bit shaggy with a variety of grasses and weeds in it, and it’s not as green. What can we do to improve the lawn so that it is more like the sod we installed?
Answer: What you describe is a common development with lawns; they change over time as the original mix of usually perennial ryegrass and fescue shifts to include some naturalized grasses and other broadleaf plants that tolerate mowing. The weeds develop from seeds blown in by the wind or may have already been present in your soil when the lawn was installed. The end product is referred to as a “climax lawn”; it now has grasses of different colors and textures, and is adapted to your site.
But there are steps you can take to improve the look, address the weeds and create a healthy inviting lawn.
A critical element of lawn management is proper mowing. Mowing at the correct height and frequency will make all the difference — a good rule, mow it high and mow it often. A good schedule is to mow once a week March through October, then once a month the rest of the year, although you probably won’t need to mow in the winter.
Keeping it long encourages the development of deeper roots, resulting in a healthier, greener lawn, which then naturally prevents weeds from growing by blocking out the sunlight. Keep your mower blade sharp and remove no more than 1/3 of the grass blade. Instead of bagging the clippings, let them fall back into the lawn. The clippings are a wonderful natural source of nitrogen, which lessens the need for fertilizer. If clippings pile up, just spread them about with a rake.
A lush lawn also needs consistent water but how often and for how long is dictated by the soil type, season and how green you wish to keep the lawn. If you have the clay soil common in our area, a shorter, more frequent watering schedule helps to wet the root zone yet avoid run-off.
If you amended the soil prior to planting, watering less often but for longer periods is recommended. As the temperatures rise, the frequency will need to increase. During hot weather a significant amount of irrigation evaporates, so watering early in the day helps minimize this loss. As for amounts, during spring and early summer, apply ¼ inch two to three times a week; use an empty tuna can or rain gauge to measure irrigation amounts, targeting ¼ inch per watering.
You can test the soil by inserting a screwdriver into the turf — if it’s dry and hard, increase the watering. Of course, if you want to conserve water usage, letting your lawn go brown in the summer is okay too; most turf grass will survive and then green up again once the fall rains return.
Another good practice for improving lawn health is dethatching, and spring is a great time. Thatch is a thick layer of grass stems and roots, some living and some dead, that naturally forms between the soil and the green blades.
Thatch left in the lawn over time grows into a thick layer ,which dries out faster than soil, causing drought stress. It is easier to remove in the spring when the grass is vigorously growing. If thatch is less than an inch thick, it can be removed with a stiff metal rake, but for thicker thatch you may need to use a power rake.
In addition to leaving the clippings on the lawn, you may also consider adding fertilizer; this helps increase the vigor and health, which helps prevent weeds from taking hold. A general rule of thumb is to apply four times per year, April, May/June, August/September and October with a fertilizer high in nitrogen (N), low in phosphorus (P) and potassium (K). Look for one with a combination of quick release and slow release sources of N.
Maintaining a healthy lawn is beneficial to your environment. Lawns help conserve soil, reduce runoff, improve air quality, sequester atmospheric carbon and reduce urban heat loads. And they create inviting areas of coolness for fun outdoor activities.
For more detailed information on lawn care in western Oregon visit catalog.extension.oregonstate.edu/ec1521