Perfect Timing

The majority of landscape professionals agree on the value of turf aeration to relieve compaction and aid thatch breakdown. They don't, however, always agree on when to aerate. Even more critical, they can't always find time to aerate, even when they know it would be beneficial.

Generally, fall aeration is considered best for cool-season turf, because grass plants are developing more roots in preparation for winter. Opening up the root zone with aeration provides an enhanced growth zone for new roots. Plus, you can combine aeration with an early fall application of slow-release fertilizer to get grass in shape for winter and charged-up for new growth next spring. Turf management schedules may be a little more flexible in the fall, too.

The key factor is to allow plenty of time for turf to “heal” after a fall aeration treatment. “Lawns need about three weeks to recover from core aeration, so don't schedule aeration much later than early to mid-September in northern areas,” says Roch Gaussoin, extension turf specialist at the University of Nebraska.

One advantage to fall aeration, besides the timing, is that you can combine it with overseeding and fall fertilization to get customer lawns in better shape for winter and a refreshed turf condition next spring.

On the other hand, spring aeration can be beneficial, as well. Gaussoin says spring aeration is sometimes more effective where winter freeze-thaw action has loosened soil already. Mechanical aerators can do a better job before the ground gets too hard and dry.

A common misconception is that spring aeration will break the pre-emergent crabgrass control barrier. “If the turf is good and dense, core aeration won't compromise the pre-emerge barrier,” says Karl Danneberger, professor of turfgrass science at Ohio State University. “If the turf is thin, you might get some crabgrass germination, but aerating probably is needed to help turf thicken up.”

With its spreading rhizomes, bluegrass probably needs more coring than ryegrass or turf-type tall fescue, according to Danneberger. “Some of the newer, aggressive bluegrass varieties can build up excess thatch. And in areas of new construction, you can pretty well count on having compaction problems because of the clay soil churned up during construction, especially where lawns have been sodded.”

Danneberger says it's important to get as many punched holes as possible when aerating. “If you have ¾-inch tines on a 2 × 2 spacing, you are covering only 11 percent of the turf area per pass. You need to make at least a couple passes to do an effective job.” If necessary, as for athletic fields or park areas, you can break up the cores and drag them back into the turf to help break down thatch.

Be sure tines are not overly worn, he adds. “After a while, the edges get smoother and the tines actually wear down so you don't get the coring depth desired. Always check aerating results to ensure you are getting deep enough penetration.”


Agronomists generally agree that increased aeration would benefit the landscape in most southern regions. “There is a perception that sandy soils don't compact, so aeration isn't necessary,” says Dr. J. Bryan Unruh, extension turfgrass specialist at the University of Florida. “Not true. Most warm-season turf could use more aeration.”

You actually can aerate warm-season turf anytime during the growing season, Unruh says. “However, I would recommend the best time is April and May. You want to take advantage of the greatest recuperative potential of the grass plant, and that is early in the season.”

Although areas in the South and Southeast generally get adequate rainfall during the summer, early aeration is a good idea to give turf a full growing season to recover.

Where lawns are not irrigated and rainfall is short, as in arid regions, even warm-season grass can go dormant in summer heat. That's another good reason to aerate early in areas of the West and Southwest where irrigation water may be short. Even in northern areas, it's best not to aerate turf where temperatures exceed 85∞F for more than a couple days, unless extra irrigation water is available to minimize stress.

Use caution when aerating grasses like St. Augustine and centipede grass, Unruh says. “Rolling type aerators, especially those with spoon-type tines, can tear up stolons in spreading grasses. They still need to be aerated, but operators need to be careful not to go too fast and leave too much damaged turf.”


While fall aeration is usually the first choice for cool-season turf, spring aeration is better than no aeration at all. Many turf managers try to aerate both spring and fall. The difficulty usually is fitting it in with the other turf maintenance chores, especially where frequent mowing and irrigating are required.

Weather and soil conditions sometimes alter aeration timing (soil should be warming and not too wet for best results). Turf use can influence timing, too. If fields are being used for soccer or football, you may have to schedule aeration after the season is over (you can use smaller tines for aeration during the season, but may still have to drag fields to remove cores and fill in the holes).

How do you tell when turf needs to be aerated? The best way is to take turf samples with a core sampler, pulling at least 3-inch plugs and checking depth of thatch and compaction layers. More than ½-inch of thatch layer means it's time to aerate to begin breaking down the excess thatch.

Watering and weed growth can give you clues to turf condition, too, according to Gaussoin. “If you see irrigation water pooling where it didn't before, it could be due to compacted soil keeping water from percolating down into the soil. Also, certain weeds tend to show up when soil gets compacted — weeds like goosegrass, annual bluegrass and prostrate knotweed. Watch for algae and moss in shady areas, too.”

A good aeration program helps thicken-up turf, which tends to reduce weed pressure and herbicide use. Stress tolerance is better, too, especially during hot summer weather.


For lawn care professionals, aeration can be a good income-generator. For most residential customers, however, it's a service that has to be sold. Unlike golf course superintendents and sports turf managers who aerate regularly, many homeowners don't understand the need for — and benefits of — aeration. Lawn care operators usually find that, once their customers understand its value, they willingly pay the extra cost for lawn aeration.

This sometimes creates a timing problem for grounds managers. The typical homeowner is more likely to spend the extra money for aeration in the spring, when he or she is thinking about green-up and restoring that nice, thick, green lawn. Results are more readily apparent, as well, with the natural flush of growth and green-up, especially as soil warms and the first spring fertilization kicks in.

Unfortunately, this is usually the hardest time for lawn service operators to schedule aeration in with other jobs, especially during an early spring warm-up when the change from winter to mowing can occur in a matter of a few days.

So how do you overcome this challenge? Go ahead and aerate lawns for your new or first-time customers. Once they see the benefits, try to switch them to a late summer/fall aeration program. What about those who want both spring and fall aeration? If necessary, buy the equipment and hire the help needed to get it done. With the right equipment and a good operator, aeration is a money-maker.

Bob Brophy is director of lawn care products at Turfco Manufacturing (Minneapolis, Minn.).

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