Why does my lawn have bare patches?

A bare patch is a symptom, and the cause usually sits right where the patch is. Shade, hard or wet soil, foot traffic, scalping, acid soil and drought account for most of them. Grubs and lawn diseases kill grass in patches too, usually in late summer. Whatever the cause, most Virginia lawns will not fill the gap on their own, so the fix is to correct the cause and reseed.

Why the patches don't fill in

Most Virginia lawns are tall fescue. Newer cultivars are marketed with short rhizomes, but Virginia Tech still recommends managing it as a non-creeping grass, and lists limited to no recuperative potential among its weaknesses.^[1] A gap in a fescue lawn tends to stay a gap, or fill with weeds. Kentucky bluegrass, by contrast, has an aggressive lateral growth habit from rhizomes^[1] and can close small holes, which is one reason a fescue and bluegrass mix holds up better. Bermudagrass and zoysiagrass spread too.

Where the patch is tells you a lot

Under or near trees. Kentucky bluegrass and bermudagrass both have poor shade tolerance, tall fescue has moderate shade tolerance, and the fine-leaf fescues are the most shade-tolerant of the cool-season grasses.^[1] As trees grow, they also change how much light and water reach the lawn.^[1] Virginia Tech notes that pruning off lower limbs or thinning the canopy improves growing conditions for the grass.^[2] In deep shade, a shade-tolerant seed mix or a mulched bed may be the honest answer.

Along paths and play areas. Compaction physically restricts root penetration and reduces the soil oxygen roots need.^[3] Henrico County's Extension office names high clay content or heavy traffic^[8] as the usual causes. A screwdriver that will barely go in, when the soil is moist, is the tell. Core aeration in the fall relieves it; a stepping-stone path fixes the route everyone takes.

In low spots that stay wet. Moss and algae are a giveaway. Virginia Tech puts it plainly: mosses thrive in poorly drained soil while all turfgrasses struggle.^[2] Seed alone will not hold there; the water has to go somewhere first.

On bumps and slope edges. If the patch sits on a high spot the mower deck catches, it is scalping. Scalping severely weakens turfgrass,^[2] and the fix is to raise the deck, smooth the bump with soil, or use a smaller mower there.

Spread across the whole lawn. Look at the soil and the mowing. Many of Virginia's soils are very acid,^[3] and a soil test settles whether pH or nutrients are the problem. Tall fescue lawns should be kept between three and four inches;^[5] a lawn cut much shorter thins out under summer stress. Our guide to mowing height for fescue covers it.

Patches that appear in summer

Drought. A lawn that browns evenly in a dry spell is usually dormant and comes back. But during an extreme and persistent drought, some cool-season grasses may die and need reseeding in the fall,^[6] and seedlings and lawns less than a year old have little to no drought tolerance.^[6] Sunny slopes and strips along hot pavement often go first.

Grubs. White grubs are soft, C-shaped beetle larvae with brown heads that feed on grass roots.^[4] Their damage usually shows in late summer and early fall: the turf yellows and looks drought-stressed, and may die in scattered irregular patches.^[4] High numbers, more than 8 per square foot, can make turf feel spongy and let it be pulled up like a carpet.^[4] Animals that feed on grubs, such as raccoons, moles, skunks and birds,^[4] may tear up the turf to reach them. Henrico's guide suggests considering an insecticide only when the average count in several 1-foot-square samples is greater than six grubs; finding two or three does not call for treatment.^[8]

Chinch bugs. Chinch bug damage is usually worse in hot, dry, sunny spots with a thick thatch layer,^[4] and it looks like drought: yellow, then brown, then dead.

Disease. Brown patch is the most common and troublesome disease of tall fescue.^[5] It shows up in warm, wet weather, and the lawn typically recovers in fall when managed properly, but heavy brown patch combined with drought or heat stress can kill plants outright.^[5] Gray leaf spot is worse: gray leaf spot can devastate a tall fescue lawn within a few days when warm, wet weather persists.^[5] If patches spread quickly in late summer, take a sample to your local Extension office before buying a fungicide.

Other causes worth ruling out

Thatch. A thick layer of undecomposed stems keeps water and roots near the surface. Virginia Tech's rule is that once thatch reaches 0.5 inch, start watching it, and at 1 inch it should be removed.^[3] Most cool-season grasses do not build much, but Kentucky bluegrass grown under moderate to high management often does.^[3]

Spills and fertilizer burn. A patch in a neat shape near the driveway or shed may be a spill. High-potash fertilizers are a known culprit: Virginia Tech advises no more than 3 pounds of 0-0-50 or 0-0-60 per 1,000 square feet to established turf in hot weather without watering it in.^[7] Spreader overlaps and turns can burn stripes the same way.

Fixing the patch

Once the cause is dealt with, loosen the soil in the patch, work in what the soil test calls for, and reseed. For cool-season grass, late summer to mid-fall is the best window.^[3] A few patches are a weekend job; if they cover more of the yard than grass does, treat it as a full renovation and follow our guide to fixing a lawn that is mostly weeds and bare spots, then keep it thick with our guide to maintaining a renovated lawn.

Stop and call a pro if

• Water pools in the patches or runs toward the house; drainage or grading may be needed.
• Grub counts are high across the lawn and you do not want to handle insecticides yourself; use a business with a Virginia pesticide license.
• Patches spread quickly in hot, wet weather and you cannot identify the disease.
• Large trees over the lawn show dead limbs, splits or root damage.

See all lawn and landscaping answers, browse lawn renovation services, or look up lawn and landscaping businesses around Blacksburg. If the patches have taken over, describe the job once and local businesses quote the repair.