Having a lush green lawn year around can seem like an unreachable goal, but, by focusing on the key practices of regular mowing, watering and application of fertilizer, the average homeowner can significantly reduce weeds and improve the quality of their turf without the use of herbicides.
The most important practice is regular mowing. When you first focus on mowing, follow the one third rule: don’t cut more than one third of the height of the grass in a single mowing. Your goal is to get to an optimal two to three inches in height. At that height, you will reduce “scalping,” where you’ve cut your grass so low that the grass stems are exposed. Since photosynthesis occurs on the blade of the grass, cutting the blade away reduces the energy the plant can create and makes the grass susceptible to environmental stress, insects and disease.
Cutting the grass too low also allows sunlight to get through to the soil where it can germinate weed seeds lying dormant on the surface. Weeds that indicate you are mowing too low include dandelions, crabgrass and annual bluegrass.
Raising your mowing height to achieve three inch height improves rooting, improves turf grass quality and can reduce weed populations by as much as half. Keeping it at the correct height requires more frequent mowing, but the benefit is an increased density of the turf. Grass in nature is grazed by various species, and that grazing promotes lateral growth; frequent mowing replicates grazing and produces the same growth benefits.
Mow at least once a week for increased growth, or you risk weeds such as lambsquarter, ragweed, purslane or garlic mustard. Mow even if your grass is sparse, and mow seeded areas when height is appropriate. Be sure to change your mowing patterns from one time to the next to minimize compaction of your soil. It’s fine to leave clippings in the grass as it adds nitrogen that would be removed otherwise.
The right fertilizer
When you fertilize, select one developed for turf grass. Fertilizers are labeled by their macronutrients: N for nitrogen, P for phosphorus, and K for potassium. Washington doesn’t allow phosphorus in turf fertilizers except for deficiencies found through soil testing or for repair of damaged grass because it encourages excessive algae growth. The important nutrient for your turf needs will be nitrogen, so compare nitrogen content in fertilizers as you compare prices.
Alec Kowaleski Assistant Professor, Turf Specialist with Oregon State University, recommends a holiday plan for fertilizing to make it easier to remember. His goal is to apply three to five pounds of nitrogen per 1000 square feet of yard in each year. He recommends applying 1 to 1.5 pounds at Memorial Day, 0.5 to 1 pound at the Fourth of July, 0.5 to 1 pound at Labor Day, and 1 to 1.5 pounds at Halloween.
You can calculate the amount of fertilizer needed to achieve that amount of nitrogen. Divide the amount of nitrogen desired by the percentage of nitrogen in the bag (0.26 for a bag with an N of 26). 1.0 pound nitrogen desired per 1000 square feet divided by 0.26 equals 3.8 pounds of fertilizer needed to supply 1.0 pound nitrogen for each 1000 square feet.
Since our Southwest Washington rain patterns typically match cool season turf grass growth, Alec recommends using quick release fertilizers in spring and fall when grass is at its healthiest state and is being mowed regularly. In summer, when grass is hot and stressed, use a slow release organic fertilizer to avoid fertilizer burn. Urea is a tempting fertilizer as it has high nitrogen and is inexpensive, but it is all quick release and can burn your grass — save it for spring and fall when grass is at an optimal state. Weeds that appear when you aren’t fertilizing include clover, plantain and black medic.
The third key practice is watering and irrigation. You will need to adjust your watering rates according to the seasons, since grass goes dormant with no water. In spring and fall, your goal is 0 to 0.75 inches per week depending on rainfall. In summer, the goal is 0.75 to 1.5 inches per week. Kowaleski suggests watering three to four times per week at 0.2 inches per watering for our cool season grasses. Since 90 percent of the roots are near the top of the soil, you will want to keep water at the surface for the most benefit.
Keep an eye on your irrigation rates to assure you don’t overwater. A commercial sprinkler head can provide 0.2 inches in just seven minutes, while a home sprinkler can take 20 minutes to produce the same amount of water. Use a rain gauge or an empty tuna can to measure the amount of water and determine the right number of minutes for your equipment.
Drought related weeds include crabgrass and sorrel. If you have moss, raise your mowing height, increase fertilization, and increase sunlight to the area.
If you are staring at a brown lawn after this summer, it may rebound with the autumn rains but not if the roots are totally dead. Keep an eye on the roots after the first week or two of rain to see if green shoots are beginning to appear. If not, you will probably need to reseed this fall to bring your lawn back. Next spring, you can begin to use mowing, fertilizer, and irrigation to make the most of your lawn.
Susan Cox is a volunteer master gardener with the WSU Extension.