If your lawn has some thin areas, the best time to plant new grass is mid-August through mid-September. The farther north you live the earlier you plant the better. Scratch the area you want to seed with a heavy garden rake so that the seeds make good soil contact. Use a starter fertilizer and water the newly seeded area gently and lightly so the seeds do not wash away from the area seeded. If there is not enough rain, water frequently. Continue to mow the lawn as needed to keep established grass from growing too tall for the sunlight to reach the new seeding. Weed killers should not be used until next year when new grass has toughened up.
One reason that lawns thin and weeds take over is because the lawn many be short on fertilizer. The best time to fertilize your lawn is in September, because the weather is starting to turn cooler and grass likes the cool seasons of spring and fall to grow vigorously. It is best to apply two applications of fertilizer. One at the beginning of September and the other late in October or on Halloween. The late application will not result in a burst of top growth, but will encourage increased root growth, and early greening-up next spring with a thicker healthier lawn.
It is important to continue mowing our lawns throughout the fall until growth stops. The weather is usually warm enough for grass to continue to grow well into October. Lawns that are left too tall at this time frequently mat down during the winter. This makes them more susceptible to winter disease problems such as snow mold and invasion by mice or voles.
The general rule of thumb for mowing lawns is to mow high, mow frequently, and allow the clippings to return to the lawn. Mowing frequently is based on the growth rate of the grass. It is best if you mow often enough so that no more than one-third of the leaf surface of the grass plants are removed at one time. If the finished height is two inches, mow whenever grass reaches three inches in height. Grass clippings an inch or less in length filter down to the soil surface and decompose relatively quickly. Longer clippings have a tendency to remain above the lawn where they appear unsightly and can shade or smother grass beneath. Long clippings need to be removed to avoid both unsightliness and lawn damage.
Most of our lawns have been growing well this year as a result of our abundant rainfall. So long clippings and clumps of grass on our lawns may be a problem at times. These should be raked off the lawn and stored in bags. Research has found that it is better to add grass clippings with mulched leaves when adding them to a compost pile. The grass clippings when mixed with leaves, help to break down the leaves more efficiently into compost.
Research also indicates that if tree leaves are sufficiently chopped up via a standard or mulching type of rotary mower and dispersed over the lawn, there should not be any problem with grass survival. It has been observed that spring green-up can be somewhat better where tree leaves have been chopped up and incorporated into the lawn surface the previous fall.
If you plan to allow leaves to remain on the lawn, it must be done cautiously and should be confined to lawns with only a light covering of leaves. (Grass blades should still be visible through leaves before shredding.) The amount of leaves deposited on the surface should be less than an inch or two prior to mowing them. Heavy layers of leaves (i.e. more than a couple of inches) should first be lightly raked off before mowing. Even after several passes over an area, any heavy accumulations of leaves such as windrows or piles should be raked off so that the grass plants underneath them are not starved of sunlight and ultimately die. A good rule of thumb as to whether or not leaves have been properly chopped up and incorporated into the lawn is that when you are done, the lawn should look like it has been thoroughly raked. The surface should be relatively free of leaves and the grass fully exposed to take advantage of those sunny fall days without being covered by a layer of leaves.
Kyle Schulz is a Wadena County Master Gardener from Sebeka, and the regular gardening columnist for the Wadena Pioneer Journal.