Home lawns have once again struggled through another hot summer however this year was much different with many areas of the state receiving continuous rainfall. Conditions were in place for turfgrass diseases to run wild – starting with zoysia patch in the spring, dollar spot on bluegrasses and ryegrasses, and brown patch in tall fescue hitting hard all summer. We have also seen conditions that are favorable for egg laying by several of our white grubs insect species. Calls were numerous all summer on lawn diseases and are presently starting to come in on dead patches of sod with no roots, indicating grub damage. This usually means loss of sod.
In most years we talk about the need for rain to bring back dormant lawns and await those cooler temperatures. Our night temperatures will begin to dip into the sixties once again and possibly the fifties into September. Many of us are also ready for cooler days with less humidity. With all this in mind, it’s time to think about some fall maintenance - some aeration followed by some fertilization and over-seeding.
Core aeration is a practice of pulling soil plugs to open the soil surface for better air exchange and nutrient and water movement. It is a practice that also helps to reduce compaction and thatch by spreading soil plugs on the surface. Soil plugs are crumbled and fall freely into aeration holes as well as spreading some soil into the thatch layer where soil microbes can feed on thatch debris. Aeration is a practice that can be done in both spring and fall and is the very best way to begin a fall fertilization program. Applications of fertilizer after aeration will move nutrients immediately into the root zone of your lawn. This practice has shown excellent results in the density and color of coolseason turfgrasses on their way to recovery from summer stresses. Spreading grass seed after aeration is also an excellent practice in lawns that have thinned considerably from summer pests.
Aeration equipment can be found at local rental stores or garden centers. Machines that pull a ½ inch diameter plug three to four inches deep on four inch centers do an excellent job. Machines that force hollow tines into the soil are better than pull-type drums with spoon tines. Not all machines will meet these specifications; however any amount of aeration is better than no aeration to kick-off fall maintenance.
When using aeration equipment as a tool for preparing a seedbed, shallow divots are only required (½ to 1 inch deep). Creating lots of divots with multiple passes is best. However, you may still want to make one pass 3 to 4 inches deep for reducing compaction.
Some lawns (mostly Kentucky bluegrass lawns) have a tendency to develop thatch as it relates to mowing frequency and varieties of grasses growing in your lawn. If you notice thatch developing in your lawn, you may need to de-thatch. Lawns with thatch up to ½-inch are generally OK, but as that thatch layer approaches ¾-inch, it’s time to rent a dethatching machine from your local rental store or garden center. It may be necessary to de-thatch in two directions raking debris each time. Set the depth of the machine until the blades barely touch the soil surface. You will notice some thinning of the turf canopy; however recovery will occur throughout the fall. De-thatching will improve the movement of nutrients and water into the root zone where they are needed. Fall is usually the best time to de-thatch cool-season lawns, since de-thatching in the spring can disrupt your pre-emergence control of summer annual weeds (crabgrass and others).
A de-thatching machine is also an excellent piece of equipment to prepare seedbeds prior to over-seeding. The removal of thatch, with thinning of the turf canopy exposing soil is a perfect situation for dropping seed into a lawn, therefore improving seed/soil contact.
Fall fertilization should always start with a soil test to determine what the needs of the soil are, if any. Soil pH is also important as it affects nutrient availability to the plants. Soil test results will give you nutrient levels, soil pH and any information about lime requirements. A soil pH around 6.5 to 6.8 is optimum. Soil pH between 6.0 and 7.0 are acceptable. MU guide #G6954, Soil Testing for Lawns gives information on how to take and submit soil samples to the University of Missouri Soil Testing Labs. This guide sheet can be accessed through the Extension Publications Website at http://extension.missouri.edu/.
Homeowners have a wide variety of fertilizers available to them for fall fertilization. Many organic fertilizers, such as Organica, Milorganite, Earthworks, Nature Safe and Ringer are available and will provide an excellent source of slow released nitrogen. Organic fertilizers do require soil microbes to release nutrients, therefore as soil temperatures decrease by late Fall, performance of these fertilizers will drop off.
More inorganic types of fertilizers are available to homeowners and can be somewhat confusing. Many products have much higher amounts of nitrogen and most are soluble forms (quick release) of fertilizers. Quick release forms of fertilizers are there and gone after about two to three weeks. You will get a quick flush of green growth, then a quick tapering off of color and growth. Find fertilizers with a good balance of N-P-K (nitrogen/ phosphorus/ potassium) with a ratio somewhere around 3-1-2. Also look at the analysis label on the bag and find a product with 30 to 70 percent slow-release nitrogen. This way your fertilizer is released over a longer period of time requiring fewer applications and allowing the plants to more efficiently utilize plant nutrients.
Total fertilizer rates for fall give best results if 2.5 to 3.0 lbs of nitrogen can be applied per 1,000 square feet. These totals should be divided over two or three applications throughout the fall on 4 to 6 week intervals. Possible combinations would include a pound of nitrogen per 1,000 square feet in early September after maintenance procedures followed by 1.5 pounds of nitrogen per 1,000 square feet in late October. A second alternative would include a pound of nitrogen per 1,000 square feet applied in early September, October and November. Most fertilizers are complete fertilizers including nitrogen, phosphorus and potassium; therefore requirements for those nutrients should be based on soil test results. Soil test results indicating high to very high amounts of phosphorus and potassium may require applications of fertilizers with nitrogen alone or lower amounts of P and K.
Winterizing fertilizers are usually recommended as the final fall application for cool-season grasses. Good winter fertilizers will have higher and equal amounts of nitrogen and potassium (first and third numbers of the fertilizer components). However, there are conflicting comments about applications of additional potassium for hardening off plants. Additional potassium does not increase plant tissue potassium if amounts of potassium in the soil are already high to very high. Your soil test will tell you this. If you regularly soil test and know that your potassium levels are high, then a winterizer fertilizer will not provide additional benefit for you.
These simple lawn maintenance items will insure good lawn recovery following summer. Improving lawn growth and density prepares for next season’s battles. Remember to mow tall (3.5 to 4 inches) and let those clipping fall!
REVISED: September 29, 2015