| Missouri Environment and Garden | Volume 8, No. 8 |
| News for Missouri’s Gardens, Yards and Resources | August 2002 |
Late summer through late fall is the best time to apply several management treatments to Kentucky bluegrass lawns as well as other cool-season species and here’s why. In late summer, Kentucky bluegrass is shifting gears from summer to fall growth as shorter days and cooler temperatures favor emergence of rhizomes (underground creeping stems) and production of new plants from these rhizomes. The new plants in turn form lateral shoots (tillers) and the turf thickens. Mechanical thatch removal and aerification is favored at this time of year because turf that is temporarily thinned by these treatments will rapidly recover and fill voids as turf thickens, root systems develop, and topgrowth slows.
Time to fertilize
In Missouri, we should begin late summer-fall fertilization about
Labor Day and finish in mid-November to early December. Our fertilizer
recommendations are based on amounts required to supply a given amount
of nitrogen per 1,000 square feet of lawn. Most lawn fertilizers are
"complete" and contain the three major nutrients: nitrogen (N),
phosphorus (P), and potassium (K). Therefore, the amount of phosphorus
and potassium applied is determined by the ratio of these two elements
to nitrogen. For example, a fertilizer with a label analyses of
20-5-10 would contain 20 percent N, 5 percent P, and 10 percent K. The
N:P:K ratio would be 4:1:2. The amount of fertilizer required to
apply 1 pound nitrogen to 1,000 square feet can be calculated by
dividing 100 by the percentage of nitrogen in the fertilizer (100/20 =
5 pounds fertilizer per 1,000 sq ft).
For routine maintenance, where soil test or experience indicates no major nutrient deficiencies, use a lawn fertilizer with an approximate ratio of 3:1:1 or 4:1:1 or 4:1:2 at the recommended rate. If a soil test indicates low phosphorus or potassium levels or where basic fertility levels are not known, use fertilizer with a ratio that more closely approximates 1:1:1 or 2:1:1 or 3:1:2. Nitrogen fertilizers are available in several forms, and lawn specialty fertilizers often contain 25 to 50 percent of the total nitrogen in slow-release form and the remainder in quickly available forms. This combination gives immediate response from the quickly available nitrogen in cool weather while the remainder (slow-release) is available over a longer interval.
Eliminate persistent broadleaf weeds.
Lawns that have more than 50 percent desirable grass in late summer, but still appear thin and weak with an abundance of broadleaf weeds, may need only fertilizer plus control of the weeds with herbicides such as 2,4-D, mecoprop, and dicamba. After weed competition is reduced, lawns may regain density. But, consider waiting for a warm day in mid-October to early November before treating. That’s because broadleaf weeds such as dandelion are transporting food material produced in leaves to fleshy, below-ground roots for storage. As this process occurs, post-emergence herbicides applied to leaves will also be translocated downward to the roots, and that’s the area you want to target for best control. Also, application of herbicides at this time of year approximates the time when you are removing your tomato plants. Tomatoes are very sensitive to many post-emergence herbicides containing 2,4-D; application at this time will eliminate the danger of injury to tomato plants.
Regardless of when you apply herbicides, keep in mind that amine forms of 2,4-D are safest because they give off fewer vapors that might drift and damage sensitive vegetable and ornamental plants. Volatile ester formulations should not be used near tomatoes and ornamental plants. Select a time when winds are calm to minimize spray drift. Using wax bars or granules impregnated with herbicides near ornamentals will help to decrease injury.
Should I renovate the lawn?
Following an average or near-average summer, we should not be too concerned if our lawns are showing stress. The reason is that Kentucky bluegrass has a system of underground, creeping stems (rhizomes) that provide a source of growing points from which new growth will emerge when cool temperatures and expected, soaking rains return in fall.
If your Kentucky bluegrass lawn has 50% or more grass cover by late summer, you may want to allow the existing bluegrass to continue spreading without interruption. However, if you are not satisfied with your lawn’s appearance and want to speed recovery, then consider overseeding. Late summer to early fall is the best time to seed cool season grasses such as Kentucky bluegrass. Cooler temperatures and expected rain at this time of year usually provide a favorable environment for germination and seedling development compared with the late spring and summer months.
Additional reasons to renovate include the following:
Steps to renovate turfgrass
One of the most important steps in renovation is placing the seed in contact with soil. This sounds simple, but most lawns have thatch, an intermingled layer of both dead and living plants, over the soil surface. This brown, decomposing layer may be up to 2 inches thick. Lawns with more than 3/4 inch of thatch should be dethatched.
Seed placed on or in the thatch layer may germinate, but the eventual stand of grass that develops will be poor. Thatch in excess of 1 inch may need to be removed with a sod cutter before reseeding. To ensure good seed-to-soil contact, use power equipment to prepare the surface for seeding. Power rakes, verticutters or vertical mowers, slit seeders, and core aerators are effective machines for preparing the surface for seeding.
Dethatching equipment is sometimes available from local rental stores. Local lawn care and landscape companies also provide dethatching and renovation service. Two to four passes over the lawn may be necessary, depending on the soil hardness and thatch thickness.
Power rakes are lawn mower-like machines that have spring tines instead of blades. The power-driven spring tines rotate in a vertical position and are designed to rip thatch out of the ground. However, power rakes that can be adjusted so that the soil surface is slightly scratched will ensure good seed-to-soil contact, but they may not loosen hard soils.
Vertical mowers are similar to power rakes except that they have fixed or flail-type blades that cut groves through the thatch and into the soil. Fixed-blade vertical mowers, sometimes called verticutters or slicers, are better at cutting into the soil. Heavy-duty, walk-behind vertical mowers are superior to power rakes for preparing a seedbed since they cut deeper into the soil, about 1/2 to 3/4 inch.
Slit seeders have discs that slice open the ground just ahead of a small tube that drops seed into the open furrow. A packing wheel follows the seed tube and closes the sliced ground.
Core aerifiers have a series of hollow tines that cut cylindrical holes in the ground 2 to 4 inches deep and about 1/2 inch in diameter. If the neighborhood kids have created a compaction problem in your backyard ball field, these machines will do double duty in helping to reduce surface compaction as well as providing an opening in soil to receive seed.
(Skip steps 6, 7 and 8 if you use slit-seeding equipment which places seed directly into the soil.)
For more information, consult the following University of Missouri Extension publications: Cool-Season Grasses Lawn Maintenance Calendar, G 6705; Cool-Season Grasses Lawn Establishment and Renovation, G 6700 ; and Home Lawn Weed Control, G 6750. These publications are available at the MU Turfgrass Center website: http://turf.missouri.edu/stat/.
John Dunn, Professor of Horticulture, UMC (573) 882-9622