Fall Recovery of Cool-Season Lawns

Published: September 1, 2011

Home lawns have once again struggled through another hot summer however this year was much different with many areas of the state receiving excess rainfall with extreme heat for an extended period of time. Conditions were in place for turfgrass diseases to run wild with brown patch and pythium working on all cool-season grasses. Moist spring conditions were ideal for egg laying of several beetles (May/June and Chafers) that could lead to white grub issues; however we have not received many reports as of yet. Dry conditions have caused several lawns to go dormant from drought and many homeowners will not realize white grub damage until cooler, moist conditions bring back dormant lawns. Calls were numerous all summer on lawn diseases; however present weather conditions have prevented many turfgrass diseases to linger. When all is said and done, many lawns still have damage and will require some fall maintenance. It's time to think about some fall aeration followed by over-seeding and fertilization.

Core Aeration
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 but is the very best way to begin fall seeding and fertilization. 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. 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.

A de-thatching machine or vertical slicer is also an excellent piece of equipment to prepare seedbeds prior to over-seeding. This equipment can also be rented and provides an excellent means of breaking up soil cores from aeration. This creates a perfect situation for dropping seed into a lawn, therefore improving seed/soil contact.

Turfgrass Selection
Turfgrass selection is an important cultural practice in turfgrass management and can have a major impact on turf quality. A quality lawn containing the recommended mixtures of species or blends of turfgrass varieties can be a difficult process and decision. Selecting turfgrass species depends on how you manage your lawn and what you expect of your lawn. Grasses differ in adaptation, cultural requirements and performance. Managing a lawn requires decisions on frequency of mowing, a fertilizer program, and your choice on whether or not to water your lawn. Selections can also be based on existing environmental conditions (level of moisture, degree of sunlight, topography) and the purpose for which the grass will be used. The answers to these questions will help you decide which type of lawn you wish to establish.

Species Selection
Blends (three to four varieties in equal portions) of turf-type tall fescues can give deep emerald green appearances with a slightly coarser texture than bluegrass. They tend to be a deeper rooting plant, therefore requiring less water than a bluegrass lawn. Tall fescue blends are recommended for lawns that receive no irrigation. Tall fescues are not as susceptible to dollar spot and summer patch, but generally will require some fungicides for the control of brown patch disease. Several varieties of turf-type tall fescues offer superior resistance to brown patch and therefore will improve turf quality. Tall fescues will tiller to help with density, but tend to be clumpy with severe thinning. They also grow well in full sun to partial shade.

Mixtures, such as turf-type tall fescues (in a blend) with Kentucky bluegrasses (90 to 95 percent fescue with 5 to 10 percent bluegrass), combine the advantages or strengths of each species to mask the weaknesses of the other. This combination will work in irrigated and non-irrigated lawns. Grass seed mixtures with perennial ryegrass should not exceed 20 percent perennial ryegrass, as it is susceptible to many more diseases than fescue or bluegrass and competes with fescue and bluegrass due to its fast germination. 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 little tolerance for direct sunlight; however their use in shade mixtures is preferred.

So which varieties do you select once you decide on a blend or mixture to plant? Various resources provide recommendations for turfgrass varieties in Missouri. Garden centers, MU Extension publications, turfgrass specialists, and other lawn care experts are good sources for information about turfgrass selections. The difficulty for most individuals is to find the varieties suggested. We will discuss several options.

Seed Tags
Grass seed bags have a seed label printed or pasted on the bag (usually the back panel). Several pieces of information on the label should be considered before purchasing seed. The seed tag will list the species (Kentucky bluegrass, tall fescue, perennial ryegrass, etc.), variety name (Kenblue, Abbey, Plantation, Crossfire II, Shining Star, etc.), purity (should be greater than 90 percent), germination (should be greater than 80 percent), weed seed content (percent), and testing date (should be 12 months or less). The species and variety name of the seed will tell you exactly what you're buying. As long as the purity and germination are acceptable, the next most important information to consider is the testing date. A current testing date less than one year old will assure the germination rate is viable.

Specific Varieties, Blends and Mixtures Available
Countless seed products are being sold over-the-counter and can be overwhelming to homeowners. However, by looking at the seed tags of products, several can be eliminated immediately. These include products that contain large percentages of ryegrasses. Many of these seed products are packaged for national sales and while they are excellent products for many areas of the country, they are not the best for the type of climate we deal with in Missouri. Concentrate more on the products that are tall fescue blends or tall fescue/Kentucky bluegrass mixtures. By doing this the selection becomes more narrow and simplified.

Species Selection
Blends (three to four varieties in equal portions) of turf-type tall fescues can give deep emerald green appearances with a slightly coarser texture than bluegrass. They tend to be a deeper rooting plant, therefore requiring less water than a bluegrass lawn. Tall fescue blends are recommended for lawns that receive no irrigation. Tall fescues are not as susceptible to dollar spot and summer patch, but generally will require some fungicides for the control of brown patch disease. Several varieties of turf-type tall fescues offer superior resistance to brown patch and therefore will improve turf quality. Tall fescues will tiller to help with density, but tend to be clumpy with severe thinning. They also grow well in full sun to partial shade.

Mixtures, such as turf-type tall fescues (in a blend) with Kentucky bluegrasses (90 to 95 percent fescue with 5 to 10 percent bluegrass), combine the advantages or strengths of each species to mask the weaknesses of the other. This combination will work in irrigated and non-irrigated lawns. Grass seed mixtures with perennial ryegrass should not exceed 20 percent perennial ryegrass, as it is susceptible to many more diseases than fescue or bluegrass and competes with fescue and bluegrass due to its fast germination.

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 little tolerance for direct sunlight; however their use in shade mixtures is preferred.

So which varieties do you select once you decide on a blend or mixture to plant? Various resources provide recommendations for turfgrass varieties in Missouri. Garden centers, MU Extension publications, turfgrass specialists, and other lawn care experts are good sources for information about turfgrass selections. The difficulty for most individuals is to find the varieties suggested. We will discuss several options.

Seed Tags
Grass seed bags have a seed label printed or pasted on the bag (usually the back panel). Several pieces of information on the label should be considered before purchasing seed. The seed tag will list the species (Kentucky bluegrass, tall fescue, perennial ryegrass, etc.), variety name (Kenblue, Abbey, Plantation, Crossfire II, Shining Star, etc.), purity (should be greater than 90 percent), germination (should be greater than 80 percent), weed seed content (percent), and testing date (should be 12 months or less). The species and variety name of the seed will tell you exactly what you're buying. As long as the purity and germination are acceptable, the next most important information to consider is the testing date. A current testing date less than one year old will assure the germination rate is viable.

Specific Varieties, Blends and Mixtures Available
Countless seed products are being sold over-the-counter and can be overwhelming to homeowners. However, by looking at the seed tags of products, several can be eliminated immediately. These include products that contain large percentages of ryegrasses. Many of these seed products are packaged for national sales and while they are excellent products for many areas of the country, they are not the best for the type of climate we deal with in Missouri. Concentrate more on the products that are tall fescue blends or tall fescue/Kentucky bluegrass mixtures. By doing this the selection becomes more narrow and simplified.

Individual varieties (from different venders) of tall fescues can be found locally. By purchasing 3 or 4 varieties of equal amounts and combining these in a large bucket or clean trash can, you can create your own blend. By adding 5 or 10% of Kentucky bluegrass, by volume, you can create your own mixture. Some of the tall fescue varieties available locally include:

Several pre-packaged blends of tall fescue can also be found. These will generally have some of the better varieties acceptable for Missouri, but it still does not hurt to check those seed tags. These include:

The next selections are Kentucky bluegrasses; some may have only a single variety, others are blends. Once again, check the seed tag to know what you are purchasing. These include:

The mixture we discussed with tall fescue and Kentucky bluegrass has several nice combinations available over-the-counter. Many venders also feel the 90/10 combination of tall fescue and Kentucky bluegrass is an excellent choice. Of all mixtures, this is possibly the best for Missouri. Products available include:

Heat and drought is always a major concern during Missouri summers for cool-season grasses. New heat tolerant bluegrasses are now available to homeowners in a packaged mix with tall fescue. Scott's "Pure Premium Heat-Tolerant Blue" includes one of these new heat tolerant bluegrasses called, "Thermal Blue." Heat tolerant bluegrasses are genetic crosses between Texas Bluegrasses and Kentucky bluegrasses that are to provide higher heat and drought tolerance. They are recommended in areas where tall fescue and Kentucky bluegrass are presently recommended. This product should be available where other Scott's products are sold.

Shade effects on turfgrass are a very common question for home lawns. Many turfgrass species and varieties are tolerant of moderate shade; however no turfgrass is tolerant of total shade. This final table does list some mixtures available for moderate shade. Just keep in mind that moderate shade should still allow at least three hours of direct sunlight daily. Anything less will produce a thin turfgrass canopy. Full shade usually requires an alternative ground cover such as vinca, English ivy or liriope.

The above information is intended to make the selection process for turfgrass seed less troublesome and give you more confidence in your choices. Be sure to always check with your local garden centers first for availability of these products, since all stores do not carry complete product lines.

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 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.

Many 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 quickly dissipated after three or four 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. An asterisk (*) next to the nitrogen source will indicate any slow-release forms of 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 (following fall maintenance procedures), 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. With sufficient fall fertilization, it may be possible to avoid spring applications of fertilizer, therefore reducing the potential for many turfgrass diseases.

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 of plants. Additional potassium does not increase plant tissue potassium if amounts of potassium in the soil are already adequate. 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 clippings fall!