Fall's the best time to seed cool season lawns

There are several reasons why fall is the most favorable time of the year to seed cool season lawns. The soils are warm so that seed, if supplied with sufficient moisture, jumps out of the ground. The speed of seed germination is determined by soil temperature.

We are moving into a climatic period of adequate moisture. Normal rainfalls will usually be sufficient for grass seed germination. If not, the amount of watering needed is usually reduced.

Because air temperatures are beginning to cool off, cool season grasses grow rapidly. Rapid growth rates are needed for quick establishment of lawns before cold temperatures of winter ensue.

And finally, crabgrass and other annual grass weed seed do not germinate in the fall. Therefore new grass seedlings do not have to compete with these aggressive weeds.

One question that does seem to pop up when gardeners are going to seed in the fall is the following: "My lawn has a lot of weeds in it. Do I spray the weeds first and then seed, or do I seed and then worry about the weeds later?"

I would suggest that you seed now and worry about the weeds after you seed for several reasons. First, if you spray with a trimec product, you will have to wait one to two weeks after application before you seed. Trimec does have some preemergent activity. In other words, for a short time after you spray this herbicide will damage grass seed as it germinates.

Secondly, I like to keep the weeds in my lawn because they become useful as mulch after verticutting. When seeding, I want to apply seed and fertilizer to the area to be seeded and then verticut the lawn in two different directions.

The process of verticutting "cuts" the seed into the soil and also chews up weed and grass foliage. This debris acts as a mulch to help keep moisture in soil. You don't need to apply straw to the seeded area.

Verticutting disturbs soil. This in turn brings dormant weed seed to the soil surface. These dormant weed seeds begin to germinate just as the grass seed does. Therefore, after seeding, even if no weeds were present in your lawn before seeding, you will find that your lawn will be full of weeds after seeding.

When your new lawn has grown to the extent that it has been mowed once or twice, apply trimec to eliminate the weeds. Trimec applied at this time will not damage new grass, and will give you a weed-free lawn for next spring.

There is one exception to the procedure outlined above. If your lawn has Dallisgrass in it you should spray glyphosate to kill this weed first before you seed. I know of no effective herbicide that will kill Dallisgrass selectively and not hurt newly seeded lawn grasses.

If you are planning on seeding your cool season lawn this fall, do it now. Don't wait until late October or November, and don't worry about all the weeds in your lawn now. Worry about them after you have a well-established new lawn.