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Growing Concerns: Some follow-up questions on fall lawn care

September 23, 2018

A reader asked several good questions as a follow-up to my Sept. 8 lawn care article. Following are his questions and my responses:

If you put down weed killer, does that affect over-seeding?

Yes, herbicides can affect over-seeding. The herbicide label will list when it can be applied in association with seeding. If you just spot treat with post-emergent herbicides, the timing of the two is less critical since herbicide is used on small areas. If you have heavy weed populations and broadcast application is required, follow label directions for proper timing of herbicide and seed applications.

What kind of herbicide do you recommend?

This depends on the species of weeds you are trying to control. You will first need to identify the weeds and find the appropriate herbicide for the spectrum of weeds you desire to control. Some of the local garden centers can be good resources for help with weed identification and herbicide selection.

If you use weed killer, is it OK to over-seed? If so, how long in between?

If weed populations are not too heavy, it would be best to seed first and apply herbicides once the grass has started growing well. If weed populations are heavy and will compete with the new seeding, you can treat the weeds and follow the label for the period of time you should wait to seed.

If weeds are a concern, put your effort into controlling them and give the lawn a chance to fill in with the new shoots from the existing turf. If you have thin areas prior to winter, put seed down in those areas prior to snow. The seed will lay dormant and germinate in the spring. If you have a reasonably good stand of grass, it may fill in adequately without over-seeding. Seed generally won’t compete with the existing turf, so the seeding does little good if you have a reasonable good stand of established turfgrass.

What is the proper order for fertilizing, over-seeding, weed control and aerating?

If you are seeding into an established lawn, mow the existing grass as short as possible to reduce competition. Next, apply a starter fertilizer followed by aerating to bring soil to the surface and to incorporate the fertilizer. Aeration has to be done heavily to bring enough soil to the surface to allow good seed-to-soil contact prior to seeding. Lightly rake the seed into the loosened soil and water or roll the area to firm the seed into the soil. If possible, apply water two to three times a day to get the new seed germinated and established.

Thanks for the follow-up questions. I am always happy to clarify or expand upon the information in my columns.

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