Fall is the ideal time of year to tackle many lawn care chores. Though it may seem counterintuitive, seeding, weed control and fertilization is most effective late in the season. With some straightforward recommendations from ISU Extension and Outreach, homeowners can ensure a healthy lawn next spring.
Perennial broadleaf weeds such as dandelion and plantain survive the winter and can live for three or more years. It’s common for homeowners to control these weeds by repeatedly spraying during the spring and summer months, but this isn’t ideal. Fall is the most effective time to use a broadleaf weed herbicide in your lawn, for several reasons. Because these perennial weeds overwinter in our lawns, as air temperatures drop and the days get shorter they must move energy and nutrients from their leaves to their roots in order to survive.
Broadleaf herbicides applied from late-September to early-November are absorbed by the weeds and carried to the roots along the same pathway that the energy and nutrients are. By moving to the roots, the herbicide can kill most broadleaf weeds with only one or two well-timed application. Lawns with heavy weed pressure or difficult-to-control weeds, such as wild violets or creeping charlie, may require multiple applications and follow-up spraying in the spring. The most effective broadleaf herbicides contain a mixture of at least two active ingredients. Always read and follow the label when using any herbicide.
A second reason to apply broadleaf herbicides in the fall is air temperature. In the heat of the summer these herbicide can more easily volatilize and cause off-target injury to other plants such as trees, shrubs, and gardens. Injury to turfgrass itself is more likely at high temperatures. After the heatwave in late-May, I saw several cases of lawns turning where herbicide has been recently applied.
Lawns will benefit from two fertilizer applications each at a rate of 1-1.5 pounds of nitrogen per 1,000 square feet. This means that if your fertilizer is 10 percent nitrogen, you will apply 10-15 pounds of fertilizer per 1,000 square feet. The first application should be made in mid-September and the second application should be made in late-October or early-November. Be sure to sweep fertilizer from sidewalks and driveways to prevent contamination of waterways. Do not fertilizer during summer months as this can encourage disease.
Seeding is best done between Aug. 15 and Sept. 30 as soil temperatures are decreasing and annual weeds are ending their lifecycles. Sow Kentucky bluegrass at a rate of 1.5-3 pounds per 1,000 square feet. It is critical to keep seedlings adequately watered while avoiding overwatering and runoff. Two light watering per day is usually adequate to keep the soil moist. Clean, weed-free straw will help conserve soil moisture. Broadleaf herbicides can cause injury to young turf, so allow several week to pass before spraying recently-seeded turf.
For additional information on lawn care or any horticulture-related topics, residents of Jasper County can contact ISU Extension and Outreach in Jasper County at 641-792-6433 or email email@example.com.