Earlier this spring, I wrote about dead and brown spots in lawns related to diseases, but there are other factors that can cause turfgrass to perform poorly. Sometimes, non-biological factors, like environmental conditions and management practices, can cause turfgrass decline or death.
Let’s look at some causes and remedies for thinning and balding lawns.
Case 1: Thinning area in established lawn
A sodded front lawn that performed well for years has thinned in one area, even though management practices haven’t changed and there are no signs of disease. Stepping back and looking at the whole lawn environment, you may notice that there’s a lot of shade over the affected area. That little maple sapling planted in the yard 10 years ago is now a big tree that created an environmental change – shade where there used to be sun. Without sufficient sun exposure, turfgrass can’t photosynthesize enough to sustain roots, and growth slows or stops as roots weaken and die.
The remedy I recommend for this case is to expand the mulch island around the tree all the way out to the full extent of its limbs. This is healthy for the tree and will prevent weeds from taking over the area where the grass failed. You can also take advantage of the shade to plant perennial hostas, heucheras, astilbe, ferns, and early spring bulbs like crocus, grape hyacinth, and daffodils that will bloom before the tree leaves begin to grow.
Case 2: A patch where grass just won’t grow
Despite several efforts at seeding and even laying a few squares of sod, there’s a patch where grass just won’t grow. In fact, not even weeds grow there. It’s that same spot where the blocks for the retaining wall were stacked a couple of years ago. Or where the boat was parked. Or where that enormous oak tree crashed down in the storm. Or where the kids used to run races. With these clues, I would suspect soil compaction as the factor preventing grass establishment and growth. Heavy weight and frequent foot traffic presses soil down and packs it hard so that water and plant roots can’t penetrate the surface or find space for growth and movement below.
Relieving compaction is the remedy for this situation. Loosen the soil through tilling or core aeration and work organic matter, such as compost and manure, into the soil to begin improving soil structure.
Extension.
Case 3: a. Part of the lawn didn’t green-up/ b. Part of the lawn just died
In case 3.a., after a very cold winter, some areas of a warm-season lawn never started growing in the spring and now they are bare. Prolonged stretches of below-freezing temperatures can kill grass roots. Similarly, a hard freeze after a nice warm spell can kill grass that has started to grow. Grass in low areas, where cold settles, and lawns with shallow roots are particularly susceptible to freeze damage and winter kill.
In 3.b., you came back from vacation to find a whole area of the lawn just dead. You made sure to set the irrigation system to water twice each week. Unfortunately, nature also contributed irrigation every day while you were gone. Oxygen is an essential need for plant roots, and saturated soil leaves little room in pore spaces for oxygen to linger, and it rots roots. Either way, the roots die, the grass fails, and there are bald spots in the lawn.
How to restore thin and bald areas in turfgrass
Once you’ve determined the cause of declining turfgrass and made changes to correct the problems, you’ll need to get grass growing in those thin and bald spots again. While tossing out some grass seed seems like an easy answer, it might not yield a restored, uniform lawn.
Timing and temperature are important factors for seed germination. Even though cool-season grasses like tall fescue are usually grown from seed, these seeds will struggle to germinate and grow during the heat of summer. Late September through October is the optimal time to reseed a fescue lawn. Seeds also need to have good, direct contact with moist soil for several days to stimulate germination.
Bermudagrass and zoysiagrass lawns are often established by laying sod. Turfgrass that grows from seed is different – in color, texture, and growth habits – from the improved turfgrass cultivars that used to grow sod. These improved cultivars often don’t produce viable seed, so they must be propagated vegetatively. The best way to ensure that restored lawn areas match the established lawn is to encourage the existing lawn to grow into bald spaces.
Fortunately, bermudagrass and zoysiagrass naturally spread through underground root structures (rhizomes) and above ground stolons that root where the nodes touch soil. To get lawn restoration started, allow the grass to grow a little higher and manipulate stolons at the edges of bald spots into the bare area. Lightly cover stolons with some soil or a small rock to hold them in place until they root.
For the centers of bald spots, use core aeration of the lawn to harvest turfgrass plugs for planting. Core aeration is also good at relieving soil compaction and stimulating root growth in the undamaged portion of the lawn. This leads to faster root spread and a healthier lawn overall. During the active growing season, you can do core aeration once each month.