Turfgrass Selection, Lawn Renovation and Fall Fertilization for Cool-Season Grasses

Home lawns have once again struggled through another hot summer. Our cool-season grasses like Kentucky bluegrass, tall fescue and perennial ryegrass have faced disease pressures, drought, insects and the reduction of root mass due to the effects of high heat. Many lawns may appear thinned out, indicating a need for some fall renovation or overseeding. Our night temperatures will begin to dip into the sixties once again and possibly the fifties in a few weeks. We will begin to receive more significant rainfalls, and the battle with summer annual weeds will come to a close with the first frost of fall. Therefore, it’s that time of the year again, when our cool-season grasses will start to thrive and recover. It’s also the best time of the year to plant new seed, open up the soil and begin fall fertilization.

A quality lawn containing the recommended mixtures of species or blends of turfgrass varieties can be a difficult decision. Selecting species of turfgrasses is dependent on how you manage your lawn and what you expect of your lawn. Managing a lawn involves frequency of mowing, how often you fertilize, whether or not you water your lawn and whether or not you use crabgrass preventers and/or products to control turfgrass diseases and insects. Once you know the answers to these questions, then you can decide which specie, or mixture of species, will work for you.

Selecting Turfgrasses:
Blends of Kentucky bluegrasses look very rich with dark blue-green colors and have pretty good resistance to brown patch disease; however, they do require more inputs of fertilizer and water to maintain that rich cover through the summer months. They are also more susceptible to dollar spot, leaf spot and summer patch diseases. Selecting bluegrass varieties that offer some resistance to some of these diseases is a practical first step in lawn establishment. Bluegrasses do develop tillers and small rhizomes, which allow bluegrasses to recover from thinning or other problems.

Blends of turf-type tall fescues can give deep emerald green appearances with a slightly coarser texture than the bluegrass. They tend to be a deeper rooting plant and therefore require less water than the bluegrasses. They are not as susceptible to dollar spot and summer patch but generally will require fungicides for the control of brown patch. There are several varieties of turf-type tall fescues that offer better resistance to brown patch than other varieties; therefore, selecting the more resistant varieties will improve turf quality. Tall fescues will tiller to help with recovery but tend to be clumpy with severe thinning. Newer varieties of tall fescue now include some that produce rhizomes (Grande, Grande II and Labarinth) very similar to the Kentucky bluegrasses, therefore providing a better ability to fill in thinned out areas.

Mixtures, such as turf-type tall fescues with bluegrasses (90% fescue, 10% bluegrass) combine the advantages of each species to mask the weaknesses of each. Mixtures with perennial ryegrass should not exceed 20% perennial ryegrass as it is very susceptible to most of the diseases listed above. Ryegrass is not very heat or drought tolerant and does not recover from thinning of cover. Unfortunately, many seed mixtures and blends available to homeowners at local garden centers contain large amounts of ryegrass (both annual and perennial) and fine leaf fescues (creeping red fescues, hard fescues, etc.). Fine leaf fescues have very little tolerance to direct sunlight. They easily burn out.

So, which varieties do you select once you decide on a blend or mixture? There are many resources available that list turfgrass varieties for Missouri. State turfgrass specialists, MU guide sheets, garden centers and other lawn care experts are good sources for information about turfgrass selections and varieties. The difficulty for most individuals is trying to find the varieties suggested. Lowe’s, Home Depot, hardware stores and other garden centers cannot carry all of the premium varieties. Sometimes the easiest approach is to list what they have and then cross-reference to the varieties listed for our area. MU’s guide sheet #6772, Cool-Season Grass Cultivars For Athletic Fields, has excellent, good and fair listings for Kentucky bluegrass, tall fescue and perennial ryegrass. While the guide sheet is written for athletic fields, the listings are excellent for home lawns as well. Information for selecting varieties can also be found through the National Turfgrass Evaluation Program (NTEP) Website at http://ntep.org for those who are comfortable searching the web. NTEP provides data tables for all turfgrass species for a number of different characteristics (quality, density, color, disease resistance, wear resistance, etc) from best to worst, averaged nationally and by location, specifically Missouri. Therefore, selecting varieties that will grow best in Missouri can be determined through a number of reliable resources.

The key to a quality lawn is to select turfgrass species and varieties that will grow best in Missouri. Finding those varieties that will offer good quality, color, density and disease resistance will make your task of lawn care a little easier. Hopefully, the selection process will become less difficult as you search the shelves of your local garden centers and nurseries.

Lawn Renovation:
Summer heat and humidity through July and August has many of us wondering why we even try to maintain cool-season grasses such as Kentucky bluegrass and turf-type tall fescue in our home lawns. Yet, even in a difficult year as we just experienced, the aesthetics of cool-season grasses keep us focused on that annual ritual of renovation and overseeding. Establishment of turfgrass brings beauty and value to any landscape and the success of a beautiful turf is dependent on many factors.

As August gives way to September, we are entering the optimum time of the year to establish our cool-season turfgrasses. Labor Day weekend is usually an excellent time to start preparations for seeding. General steps to successful turfgrass establishment include several items.

First, obtain a soil fertility test for fertilizer recommendations. Knowing which nutrients are sufficient and which ones are needed will determine optimum fertilizer needs. The pH of the soil is also important to know and a pH range of 6.5 to 6.8 is excellent for turf establishment. Any lime requirements to raise pH will be specified on the soil test results. Having this information in hand prior to seeding can save you time and money when trying to establish turfgrasses. Starter fertilizers (e.g. 10-24-18) are usually recommended at a rate of one pound of nitrogen per 1,000 square feet at time of seeding, but again this is dependent on your soil test results.

Preparation of the site includes the removal of any debris such as rocks and a visual inspection to make sure the grade or slope of your landscape is adequate for good surface drainage. Holes from rock removal or low- water holding pockets need to be filled in to insure proper drainage. Poorly drained areas are detrimental to maintaining healthy turf. Site preparation should also include any broadleaf weed control if infestations are high. Perennial broadleaf weeds such as dandelion and plantain should be controlled at this time of the year. Trimec or Weed-B-Gone are excellent over-the-counter products available to homeowners. Labels for these products usually recommend three weeks between spraying and seeding; therefore, start early if controlling broadleaf weeds first.

If you choose to renovate your lawn to different species of turf (bluegrass to fescue or vice versa), an application of Roundup is needed to kill out the old turf. Roundup herbicide can be purchased at any home and garden center and be sure to follow the label for application instructions. In seven to ten days a second application may be necessary to pick up any areas missed in the initial application. If your old lawn is totally brown, then soil prep and reseeding can take place seven days after the final application of Roundup.

If your lawn only requires overseeding to fill in thinned areas or small spots from summer disease or drought, then Roundup is not required and seeding can proceed.

When seeding, it is important to have good seed/soil contact to improve seed germination. If you choose to renovate with Roundup, you have the option to till the soil and create a fine seedbed. When tilling the soil, straw will be needed to prevent erosion at a rate of one bale per 1,000 square feet. Other methods to insure good seed/soil contact include a power rake or vertical mower. These types of equipment work up the top ½" of soil and can be used for complete or partial renovations. The best method of planting seed is with the use of a slit seeder. This piece of equipment actually plants the seed in the soil about ¼" deep. Again, you have better seed germination and less chance of the seed washing away in a heavy rain. Equipment of these types can usually be rented at any local rental or hardware store.

Seeding rates for Kentucky bluegrass should be about 2 to 3 pounds per 1,000 square feet. Turf-type tall fescues can be seeded around 6 to 7 pounds per 1,000 square feet. Mixtures of tall fescue with Kentucky bluegrass should be seeded at 6 to 9 pounds per 1,000 square feet. Seed applications following tillage, power raking or vertical mowing should be raked in lightly to help cover the seed with soil.

The final step to a successful lawn renovation is proper watering. The first two weeks following seeding are the most critical. Until the seed germinates and starts to put down a root, seed can wash away very easily. You should keep the soil surface moist, not wet. Do not let seed dry out once it starts to germinate. On warm, windy days with lower humidity, it may require several light waters a day to keep the surface moist. Always avoid puddling and runoff.

In a successful renovation, seedling turfgrass should be up and growing in 10 to 14 days. If your renovation takes place in the first half of September, you will be mowing your new lawn once or twice late in the fall. One month after you notice new seedlings, we recommend an additional fertilizer application of one pound of nitrogen per 1,000 square feet of a good, complete fertilizer (e.g. 24-4-12). Our recommended fall seeding program can start Labor Day weekend until October 1.

De-thatching and Aeration:
Some 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" are generally OK, but as that thatch layer approaches ¾", it’s time to rent a de-thatching machine from your local rental store or garden center. Soils in your lawn also have a tendency to become hard and compacted, limiting good root development which is necessary for a healthy lawn.

De-thatching can reduce that thatch layer, and 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 preemergence control for crabgrass.

Aeration is a practice of pulling soil plugs to open the soil surface for better nutrient and water movement as well. 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. Aeration 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 cool-season turfgrasses on their way to recovery from summer stresses.

Aeration equipment can be found at local rental stores or garden centers as well. A machine that pulls a ½" diameter plug three to four inches deep on four inch centers will do an excellent job. Machines that force hollow tines into the soil are better than pull-type drums with tines. Not all machines will meet these specifications; however, any amount of aeration is better than no aeration to kick off fall fertilization.

Fall Fertilization:
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 also give you the soil pH and any information about lime requirements. A soil pH around 6.6 to 6.8 is optimum. Soil pHs 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 XPLOR Website at http://muextension.missouri.edu/xplor/.

Homeowners have a wide variety of fertilizers available to them for fall fertilization. Many organic fertilizers such as Milorganite, Sustane 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 may 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 weeks. You will get a quick flush of green growth and 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 ingredient label on the bag and find a product with 30 to 70% 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.

Fertilizer rates for fall fertilization give best results if 2.5 to 3.0 lbs of nitrogen can be applied per 1,000 square feet. Amounts should be divided over two or three applications throughout the fall. Possible combinations would include a pound of nitrogen per 1,000 square feet in early September after aeration and/or de-thatching, 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 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.

Winterizing fertilizers are usually recommended as the final application of the fall. 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 potassium for hardening off plants before winter dormancy. Plants harden off by reducing the amount of water in plant cells and therefore reducing the threat of winter freezing. It is a practice of higher importance for warm-season (bermuda and zoysia) grasses as opposed to cool-season grasses.

Any additional questions about lawn renovation, selecting turfgrasses or fall fertilization can be directed to the MU Turfgrass Research Center @ (573) 442-4893.

Brad Fresenburg, UMC Extension/Research Associate, Turfgrass Research Center, (573) 443-4893