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By Dr. Eric Miltner, WSU Turf Agronomist
Most landscapes include lawn or turfed areas. These green spaces can be useful and beautiful. But during the past five to six years, lawns and some turfgrass areas have been targeted as using too much water, too many nutrients and receiving excessive pesticide applications. The negative message would make the public believe that lawns are environmentally unfriendly.
This definitely does not have to be the case. One of our biggest problems is increasing population, decreasing green space (covered with grasses, shrubs and trees) and increasing impervious surfaces (concrete, asphalt, and rooftops).
As development in the Pacific Northwest continues, healthy lawns can serve an important role by slowing the runoff of water, preventing soil erosion, and maintaining soil permeability, thereby conserving water. In addition, lawns provide the aesthetic and functional value that many of us love.
Now is an ideal time to do some renovation after winter. Doing these lawn care practices will promote healthy grass and improve rooting for the summer drought season. The grasses grown in the Pacific Northwest produce most of their roots in the spring and the fall. No matter what we do, the root system becomes smaller during the summer.
Spring practices such as moss control, thatching, aeration and reseeding are critical in order to thicken up the lawn and get it healthy before the heat and drought stress of the summer.
In the maritime climate of the Pacific Northwest, lawns often become a mixture of several different grasses, such as bentgrass that moves into the sodded or seeded lawn, plus a substantial component of moss. Our wet, cool, winters with low light levels are better for moss growth than grass growth.
The healthier the grass is in the fall, the less moss will invade over the winter. It is very evident this spring which lawns received late fall fertilization, as they have far less moss than those that did not.
As the soil begins to dry out, we can evaluate whether we need to apply a moss control product. The most effective control will be achieved with a fine granule or liquid product. Most of the products available for moss control contain a form of ferrous sulfate, (iron) and we must take extra care to apply the materials only to the lawn.
Any moss control product which gets on a sidewalk or driveway can stain the surface. These errant granules must be swept back into the lawn or landscape. If these granules are washed off the surface they can go directly into stormwater drains. Following application the moss will turn black, and should be raked out of the lawn to open up areas for new grass seed.
Before seeding, aerify your lawn. Core aerifiers are available at many local rental centers, or a professional landscape maintenance company can provide this service. This machine pulls small cores of soil from the ground, leaving open holes for oxygen to get to the roots of the turfgrass plants. Aerifying once every year or two to relieve compaction is a good idea even if moss is not a problem.
The cores can remain on the lawn to dry out and be chopped up with your lawn mower. Coring your lawn also helps in limiting thatch build-up. Following coring, spread seed (perennial ryegrass, or fine fescue in very shady sites), especially in areas where a lot of moss was removed. Some of the seed will fall into the aerified areas, enhancing germination. Ryegrass germinates in about five to seven days, and fescue takes a few days longer. There should be enough natural moisture at this time of year to promote good germination and establishment. These practices should help increase the density of your lawn, helping the turf out-compete moss.
Fertilizing the lawn
Proper fertilization is important in maintaining a healthy lawn that resists environmental stress, including competition with weeds and moss and drought stress. Because Spring and Fall are periods of optimal growth, these are the most important times to fertilize. We recommend the use of slow release fertilizers. Natural organic and synthetic organic fertilizers (such as IBDU, sulfur or polymer coated urea, or methylene urea) behave similarly once they are applied to the soil.
Although some people feel that natural organic fertilizers provide added benefits to soil health, research has not shown this to be true as a general rule. The natural organic nutrient sources in these products are often supplemented with synthetic plant nutrients anyway. The most important thing to remember is to use a slow release fertilizer. Extensive research around the country has shown that when these materials are applied properly there is very little risk of surface or groundwater contamination, and they provide an even feeding, which is better for your lawn. Remember to sweep granules off pavement to prevent washing into storm drains.
Turf fertilization practices for the entire year are built around what you do in the fall. Apply fertilizer in early to mid September to promote regrowth from summer stress. Another application in November is important in keeping the grass competitive with moss through the winter. If you did fertilize this past November, you probably don't need an early Spring fertilization. If not, your lawn is probably ready for fertilizer now. Again, use a slow release fertilizer so that you don't promote a big flush of growth. Fertilize again in early June so that the grass has the nutrients it needs to grow at a moderate rate through the summer stress period. If you want to maintain a lawn of moderate quality, a minimum of three fertilizations through the year is needed.
Additional light fertilizations can be added if you are looking for a higher quality lawn. In general, you should apply no more than one pound of actual fertilizer nitrogen per 1000 square feet at a time, although this rate can be increased to 1.5 pounds in the fall when using slow release products. (If the fertilizer analysis is 24-4-12, for example, it contains 24% nitrogen.) To apply 1 pound of N per 1000 square feet, you need to apply 4.2 pounds of fertilizer (1 ÷ 0.24 = 4.2). Return clippings (grasscycle) when you mow to recycle nutrients into the lawn.
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