Kim Sullivan, UM Extension Master Gardener in Anoka County
Kids head back to school, trees start to show their true colors, and it’s THE best time of year to take care of your lawn. Everything you do this month can help minimize water use, chemical use and save you time as we look ahead to next year, too.
In September, temperature and moisture stress are less, and weeds stop germinating. Grass roots grow deep this time of year, taking up and storing nutrients to survive the winter and green up in the spring. Broadleaf weeds will take up weed control products pretty easily. Grass seed germinates well in the first half of September and hardens off before frost.
Continue mowing. Leaving the clippings on your lawn improves the soil, improves water retention, sequesters carbon on-site, and means you can eliminate one fertilizer application per year. Water at about an inch every 10 days if we don't have rain, or when you can see a footprint in your grass.
Separate your weed and feed. Fertilizer can be applied earlier and needs to be watered into the soil. Broadleaf weed killer is sprayed on and needs to dry on the plant, not be washed off right away.
For fertilizer, look for an NPK ratio of 5-0-7 (your bag might say 15-0-21 or 10-0-14). More nitrogen (the first number) will make the grass blade grow more vigorously, using up too many food reserves. Having a higher potassium level (K, the last number) helps the root be stronger over the winter. The other thing to watch for is 35 – 50 % of the “N” as a slow-release nitrogen. Words like polymer-coated and methylene urea mean slow release. Fertilize now through mid-September.
Weed control is most environmentally friendly when weeds are small. Hand pull when possible, and leave patches of clover for the bees. If you need to chemically treat weeds, know the weed you’re trying to kill. Many weed control products are selective, and work better on one plant than another. Please – always read and follow label directions! Spot-treat rather than whitewash your lawns, and be very careful of overspray. Treat broadleaf weeds now through mid-October.
Last, if you dig an area of your lawn and thatch is greater than the size of a dime, it’s time to dethatch. Rent a vertical mower to do the job right. To check on the need for aeration, stick a screwdriver into the soil. If it goes down 6 inches without a fight, that’s good. If not, consider renting an aerator that pulls a plug from the lawn. It’s the only method that really opens up the soil. Leave the plugs on the lawn to decompose. If you do them both this year, dethatch first, aerate second. Aerate and dethatch now through early October.
If you can’t do it all, do one or two things this fall, and make one proper fertilization. Then, watch for an article in the spring and we’ll talk more about the second-best time of the year for lawn care. For more information, see: http://www.extension.umn.edu/garden/turfgrass/lawn-care/ .