Lawn experts understand that two ways to keep a lawn healthy and green are to aerate and overseed it from time to time. Aeration gets much-needed oxygen into the roots of the grass, while overseeding fills in those areas of the lawn that are sparse or bald. It’s called overseeding because the gardener adds more grass seed than might be necessary for the area. This makes up for the seeds that don’t germinate.
When to Aerate
A lawn may need aeration if it’s looking careworn, and water takes a long time to penetrate to the roots. A gardener can check if the lawn is compacted by digging out a six-inch section and looking at the roots of the grass. If they are two inches or less and the lawn is more than a year old, it probably needs aerating.
The season to aerate depends largely on what type of grass makes up the lawn. There are two basic types of grasses: cool season and warm season. Cool season grasses experience their most vigorous growth in the spring and the fall, and warm season grasses have their best growth in the summer. Besides this, the USDA hardiness zones that apply to other kinds of plants don’t apply to grass. With grass, the map is divided into areas that are cool, warm, or arid, and the cool and warm areas are further subdivided into areas that are dry or humid. Because of this, there are places in the country where both warm and cool season grasses can be grown together.
When it comes to aeration, cool season grass should be aerated in the fall or the spring while warm season grass should be treated during the summer. However, no grass should be aerated if it’s been stressed, as it would be during a drought or a period of intense heat.
One problem with aerating cool season grasses during the spring is that the aeration can bring weed seeds to the top of the soil. A gardener can discourage weeds by adding fertilizer and a weed killer after the lawn has been aerated. The weed killer should be pre-emergent, which means it stops the seeds from germinating. If this is done, the area shouldn’t be overseeded because the weed-killer kills the grass seeds as well. A lawn with cool season grasses should also be mowed a couple of times before it’s aerated to make sure it’s growing energetically.
Aeration should be performed when the lawn is fairly dry. The lawn should then be watered after aeration.
Aerating the Lawn
Aerating the lawn is fairly easy for a DIYer, but a homeowner who has a large property might want the services of a professional lawn care contractor. Aeration takes about half a day for an average sized lawn.
The gardener should deeply water the lawn a couple of days before the aeration though the soil should not be waterlogged during the aeration. The gardener should use a core aerator over the grass and should treat areas only once. If a professional landscaper isn’t employed, these machines can be rented at garden centers or big box stores. The core aerator pulls cores of soil out of the lawn, and they should be left on the lawn and allowed to break down. The gardener should fill the resulting holes in the lawn with compost, then overseed it if weed killer hasn’t been used.
Many lawn experts recommend overseeing right after aeration. The churned up soil allows the seeds and soil to have better contact, which encourages the seeds to germinate.
Some homeowners with a small lawn simply broadcast the seed by hand, while others fill a spreader with seed and push it over the lawn. After the seed has been spread, the lawn should be watered twice a day until the seeds have sprouted and are the same height as the other blades of grass in the lawn.
Homeowners should also know that some grasses don’t need overseeding. Overseeding mainly benefits lawns that are made of cool season bunch grassed such as fescues, Bermuda grass, and annual ryegrass. Most other grasses spread through underground runners and don’t need to be reseeded unless they are damaged.