By all measures, this has been a banner year for growing grass. Record rain in June combined with showers most of the summer means the dozing period for our lawns was almost eliminated.
So why are there big brown patches of dead grass all over my 2-year-old sod? Why is grass in many places turning an off-color toward yellow?
The answers are as varied as they would have been in some of our more drought-prone summers, just in different directions. Diseases have been rampant this summer and spring fertilizer applications have been exhausted, leaving lawns to starve.
Just because there’s been more mowing to do this summer doesn’t mean there isn’t renovating that needs to be done to many lawns. Next spring is too late to correct these problems, and next week may be too late if you expect your grass seed to make a good stand before winter.
Now is the best time of the year to try to thicken a lawn because of the warm soil temperatures, cooler air temperatures and more regular rainfalls. Making your turf greener or denser may take nothing more than a fertilizing; usually, however, there are at least some problem areas that require more analysis and effort.
“If you have areas that have died out, figure out what’s the major reason, if it’s something related to soil, like sod over pure clay,” says Bruce Spangenberg, a University of Illinois Cooperative Extension educator in horticulture. “If you have a hard time tilling the soil up, you’re better off adding soil amendments and starting from scratch. If the soil is in good shape, the cause is probably from drought, insects or disease, so slit seeding or overseeding is no problem. Gear it to the soil conditions.”
Sod often is difficult to establish because the roots typically grow to their original depth and don’t seek water in the clay below, creating what’s called an interface problem. Many times, sod is grown on peat soils that have an acidic pH and are expected to knit to the predominantly alkaline soil in the Chicago area. “In new developments, we typically get the calls two to three years after their sod is put in and usually it’s a thatch or disease problem,” says Spangenberg. “In most cases, it goes back to the soil not being prepared properly.”
Ken Bilow, turf specialist at the Chicago Botanic Garden in Glencoe, says diseases are showing up this year because they never went dormant over the summer. “I’ve been seeing dollar spot, rust and red thread,” which indicate low nitrogen content in the soil, he says. “Typically, you can fertilize and grow the disease out instead of using fungicides.”
Bilow also has been observing necrotic ring spot, which he says indicates the opposite-an overfertilized lawn.
If you have dead spots where the turf pulls up easily and reveals fat white worms, your lawn has been invaded by grubs. “It’s not too late for grub control,” says Bilow, indicating the need for a special lawn insecticide. Then, “start watering heavily and the vast majority of times, the grass will perk back up and come around,” he advises.
Overseeding
Sod is still available at many garden centers, but if you act in the next week, you can overseed your lawn and get a good stand started by winter. Even if your lawn is in decent shape, it could stand some new bloodlines in the form of newer varieties of grasses that stand up better to drought, insects and diseases.
The Lawn Institute estimates that more than half the lawns in the U.S. are 7 years old and older, meaning your grass plants are more susceptible to dying out from disease. New varieties of Kentucky bluegrasses, perennial ryes and fine fescues fend off drought and those disease spores better than those available when your lawn was originally seeded.
“There are two terms to keep in mind with grass seed,” says Spangenberg. “A mixture is a combination of two or more species, such as Kentucky bluegrass with perennial rye and fine fescue. A blend is a combination of two or more cultivars of the same species. With bluegrass, the package might contain three or four cultivars. The more you get the better off you’ll be, because they will all have different resistance to drought and disease and you’ll have a more diverse lawn.”
The key to good overseeding is getting rid of thatch and weeds so the seeds make good soil contact, and then keeping them moist with light waterings daily “or twice daily if they need it,” says the Botanic Garden’s Bilow. Lawns can be raked or you can rent a dethatcher that uses vertical blades to cut the matted organic layer. These machines are preferred to rotary mower attachments, which do more damage than good.
A better way is to “core aerify” the lawn, then seed, Bilow says. A core aerifier lifts plugs of soil out of the lawn and then deposits them on the surface. Bilow says the key is to get many holes per square foot by going over the lawn several times. These machines can be rented or professionals can be hired to provide the service. The smaller machines can be difficult to wrestle with, especially to turn, and may not take out as deep a plug as the professional models.
Bilow says aerifying “allows for water to reach deeper in the soil, for greater root depth, it relieves compaction, it helps reduce thatch by enhancing microbial action and fertilizer can be taken up better by the root system.” Aerifying can be done at any time of the year and is especially needed on sodded lawns to break the interface. Core aerifying helps keep diseases from getting a foothold in the lawn, he notes.
Another option is to “slit seed” the lawn, using a piece of equipment that can be rented at some rental centers. (A slit seed machine first slits into the lawn with tangs and then deposits grass seed.) But this job probably is done better by professionals.
If you have bare spots, the surface of the soil should be loosened and a mulch applied after seeding to retain moisture. Straw is an excellent choice and it can be mowed over when the grass grows through it.
If your lawn is predominantly bluegrass, overseed with bluegrass. Much is being made of the durability and drought tolerance of the turf type tall fescues, but they are a clump-forming grass that would look funny if combined with bluegrass.
Fertilizing
Fall is the optimal time to feed a lawn but if you are reseeding or overseeding, you should use a formula that is low in nitrogen and high in phosphorus, Spangenberg says. “You don’t want too much nitrogen available at the time the seedlings are coming up,” he says. “You can use a starter fertilizer and put down a light application, say a 5-10-10 (ratio of nitrogen to phosphorus to potassium), and not go with a full rate nitrogen fertilizer until next spring.”
Bilow looks for organic fertilizers, either natural or synthetic. “I tend to stay away from petroleum-based fertilizers,” he says. “You typically pay more for organics and they are lower in nitrogen but I like them for the microbes they add which reduce thatch.” For regular applications, Bilow will add more nitrogen so he comes up with a 3-1-2 ratio of nitrogen to phosphorus to potassium.
Weed control
“When spraying for broadleaf weeds, you get better control in the fall than in spring,” says Spangenberg. “Dandelions, for example, are storing up food in their root systems and you get more of a permanent control. We recommend people spot treat unless their entire lawn is infested.”
Treating entire lawns with weed and feed products is “not enviromentally sound and a waste of money,” he says. And for those of us who are trying to start new grass, herbicides should be kept well away from the tender new sprouts for at least a season.
Dandelions can be controlled “pretty well” by products containing the herbicide 2-4d, Spangenberg says, but for tougher perennial weeds, a product containing a combination of herbicides is needed. “It’s important to get dicamba as one of the ingredients.”
Spangenberg says gardeners should not be worried that a product contains three herbicides. “As with all pesticides, you should use caution and apply only when absolutely needed,” he says. “Read the label and use at that rate. Don’t double or triple it.”
Bilow says he prefers herbicide sprays to granular formulas. For hardier weeds, two to three applications will have to be used 7 to 10 days apart, he notes.
“Do it when it is fairly calm and not very hot because you don’t want the spray to volitalize and affect surrounding plants,” Bilow says. Pets and children should not use the lawn for “awhile,” depending on what material is being used, he adds.
One of the most annoying perennial weeds that isn’t fazed by broadleaf weed killers is quackgrass, which is distinguished by its wide blades, round crown habit and purple blade bases. “You can pull it out,” says Spangenberg, “but some of the rhizomes will probably break off and then it will come back.
“If it has a good hold, it’s probably better to use a herbicide such as Roundup,” which kills any green plant it touches, he says. It is one of the most environmentally safe chemicals on the market because it breaks down quickly and completely. By the time the clump of grass dies in a couple of weeks, it will probably be too late to start new seed, but be ready in the spring to fill in that spot. A little effort now can pay off next year with a far better lawn.
