Let’s Plant New Grass

Lawn Renovation – Part 2

By Gil Medeiros, Fairfax Master Gardener
Achieving a lush, beautiful lawn is a multi-step process. Last month, we explained the preparatory work and decisions you need to make before starting a lawn renovation (see Lawn Renovation Part 1). This month, in the steps outlined below, we describe the work to plant a new lawn or fill bare spots.

1.  Clear weeds. Remove thatch and other debris.
For the grass seed to germinate, the seed must be in contact with soil. Therefore, anything that obstructs seed-to-soil contact must be removed. The most common obstructions are weeds, thatch and dead grass.

With weeds, your best bet is probably pulling them out of the ground. Another option is to use a weed killer containing glyphosate, but glyphosate is not selective; it kills any plant that comes in contact with it. There are many selective herbicides that are labeled for both broadleaf weeds and crabgrass. August, however, is not a good month to use broadleaf weed killers because the weather is too hot. Do not use a broadleaf weed killer on a day when temperatures are expected to exceed 85 degrees. On hot days, one of the active ingredients (2, 4 D) evaporates from the surface of weed leaves, and the vapor may be carried by the wind to harm valuable plants in your landscape.

dethatch rake

Dethatching rake

Thatch and dead grass may be removed with a stiff, steel rake or a dethatching rake. For a large property, you may want to rent a verti-cut machine. These have blades that slice through thatch and grass vertically, making it easier to remove the thatch and expose the soil.

2.  Apply soil amendments, such as lime and starter fertilizer
In Part 1 of this series, we talked about the importance of measuring your lawn and getting a soil test done. This is where that information comes in handy. The soil test results will tell you how much material to add per 1,000 square feet. The lime recommendation will be based upon achieving a pH of 6.2 to 6.5. Most soils in Northern Virginia have a lower (more acidic) pH, and adding lime to raise it is very common.

Pay attention to how much your bag of fertilizer or lime weighs. Let’s say you have a 30-pound bag, and the part of your lawn you want to treat measures 5,000 square feet. Your soil test report recommends that you add 1 pound of fertilizer per 1,000 square feet. To cover 5,000 feet–at 1 pound of fertilizer per 1,000 square feet of lawn–you would need 5 pounds of fertilizer.

spreaders

Drop spreader on left, rotary spreader on right

If you don’t have a scale to weigh the fertilizer (most of us don’t), estimate how much you need and pour that into your spreader. In this example, that would be one-sixth of the bag contents (5 pounds out of 30 pounds). Set the spreader to a low delivery setting, and make multiple passes over your lawn until you have spread all the fertilizer. If you make the first pass going north and south, make the second pass going east and west, and continue to alternate your paths until the fertilizer is all spread.

3.  Loosen the soil
It is important to loosen at least the top inch of soil. Loosening provides enough soil to cover the seed after you have applied it. Generally, one uses a stiff, steel rake to accomplish this task. You may choose to use a rototiller. However, using a rototiller generally loosens the soil to a depth greater than 1 inch. This brings weed seed to the surface, which you will have to deal with later.

The depth will also be dependent on the compaction of the soil and the amounts of soil amendments you need to add. Till deeper if the soil is hardpan. If you are advised to add large quantities of lime or fertilizer, you cannot simply leave all of it sitting in the top inch of soil. In this case, you will need to till to a depth of about 6 inches to mix the amendments into the soil.

4.  Water the soil
If the soil is very dry, apply an inch of water before you spread the seed. Water that is already in the ground gives the new roots something to absorb after they emerge from the seed. Watering after you have seeded will be necessary to keep the seedbed moist.

5.  Spread the seed
For a large area, you can use the same spreader you used in step 2. Follow the instructions on the bag of seed regarding spreader settings and amounts. For a smaller area, sow the seed by hand. A common mistake is to use too much seed. Keep in mind the guidance on the bag about the amount of seed to use for a given area, and check yourself periodically. A rule of thumb: If the seeds are touching each other or overlapping on the ground, you are using too much.

straw

Straw applied as mulch over grass seed

6. Cover the seed
Either rake loose soil over the seed, or apply material to the seedbed after you have put down the seed. Raking loose soil must be done carefully so as not to disturb the even distribution of seed you achieved in step 5. If you are applying material after seeding, you can use finely milled compost or topsoil and no more than a one-quarter inch of it atop the seed. Compost is better than topsoil for this because it absorbs more water and holds in contact with the seed.

You may also choose to place straw atop the seeded area. Straw helps the seedbed retain moisture. The recommended rate is one-and-a-half to two bales per 1,000 square feet. Leave the straw in place after the grass comes up.

7.  Water daily in the morning
Grass seed needs warmth and moisture to germinate. Keep the seedbed moist by applying a fine spray of water each morning until the grass is about an inch tall. In hot weather you may need to water 2 or 3 times per day. The new lawn needs regular watering for 30 days after planting.

Don’t mow the new grass until it has reached a height that is one-third greater than your planned mowing height. So, if your planned mowing height is 3 inches, one-third more in height equals 4 inches. Wait until your new grass is 4 inches tall before the first mowing.

Next month we will provide tips on fertilizing and mowing your lawn.

References
Establishing Lawns, Virginia Cooperative Extension 426-718, 2009
Spring and Summer Lawn Management Considerations for Cool Season Turfgrass, Virginia
   Cooperative Extension 430-532, 2009

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