Why fall beats every other season
Tall fescue, Kentucky bluegrass and perennial ryegrass are cool-season grasses. They grow best in mild weather. In early fall, warm soil speeds up germination, cooler air is easier on young seedlings, and fewer weeds are competing for the same ground. Seed that goes down in September has the whole fall to root in before winter.
How to do it, step by step
- Mow a little shorter than usual and bag or rake off the clippings so seed can reach the soil.
- Water the day before if the soil is dry. Core aeration works best when the ground is moist, not rock hard and not soggy.
- Core aerate. The machine pulls small plugs of soil out of the lawn. Make a second pass in a different direction over compacted spots. Many Maryland yards sit on clay that compacts easily. Leave the plugs on the lawn; they break down in a few weeks.
- Overseed right away. Spread a seed blend that fits your light: a tall fescue blend for sun, a shade mix for shade. The aeration holes give the seed good contact with the soil.
- Keep the top inch of soil moist. Water lightly once or twice a day until the seedlings come up, which takes anywhere from one to three weeks depending on the grass. Then water less often and more deeply.
- Be patient with the first mow. Wait until the new grass reaches normal mowing height, use a sharp blade, and read the label before using any weed killer on new seedlings.
What about spring?
Spring is the backup window, roughly late March through April once the soil starts to warm. The catch is that most crabgrass pre-emergent products also stop grass seed from sprouting, so you have to choose. If you seed in spring, skip the usual pre-emergent or use a product labeled for use at seeding, and plan to pull weeds by hand. Spring seedlings also have only a few weeks before summer heat arrives. If crabgrass is your main worry, wait and seed in the fall instead.
How often should you aerate?
Many lawns do well with aeration and overseeding every year or two, especially if the soil is compacted, the lawn is thin, or it gets a lot of foot traffic. A thick, healthy lawn may only need it every few years. If you are not sure, a quick look at the soil and the thin spots will tell you.