Depending on the types of fertilizer you’ve used and the potency of the weeds in your lawn, you may find weeds in a newly seeded lawn fairly quickly. One way to prevent this is to carefully remove all existing grass, weeds and topsoil before applying new topsoil and grass seed. Unfortunately, weed pieces and seeds can easily be left behind in the dirt if you do not thoroughly clear your lawn before applying new seed.
When it comes to the growth of weeds, Daily Gardener explains that the best defense is a good offense. If you haven’t yet laid your grass seed, be sure all existing weeds are pulled up at the root, including those growing near the area you’re seeding. Use weed killer before seeding your lawn if at all possible.
Treating Weeds in New Grass
By properly maintaining your lawn, you can avoid the growth of weeds and enjoy lush, beautiful grass. Keep your lawn watered and fertilized if appropriate. Knutsen suggests fertilizing a new lawn between four and six weeks after you plant it. They also suggest that if weeds do crop up before the four to six weeks are up, you can remove them around the eight- to 10-week mark.
Keep gardens and wooded areas clear of weeds whenever you can to prevent the spread of weeds into your newly reseeded lawn. If you notice that weeds are beginning to encroach on your grass, pull the weeds as quickly as possible.
Weeds in new turf may also be the result of low-quality grass seed. Believe it or not, some products may contain seeds for weeds in addition to the grasses they purport to have. Check the package of your grass seed carefully and ensure that it says “weed seeds 0 percent” before you apply it to your yard. This will give you the best shot at a weed-free lawn.
However, you can get rid of these weeds just as fast as they have appeared.
The important thing to remember when new weeds appear in your newly sown lawn is not to act hastily – do not apply a Feed, Weed and Moss Killer type product of any kind on a newly sown lawn.
If you find that the weeds are recurring past the 6-8-week mark, you may wish to consider using a selective herbicide to spot spray your weeds. Some weed killers such as glyphosate (Roundup) kill more than just weeds, so it is important to not apply these as if they are not done precisely, they can kill your grass. Shop bought selective weed killers will recommend when to apply their product and how often and you should read the instructions thoroughly and adhere to them.
In short, here’s what you should do if you encounter weeds in your newly seeded lawn:
Although this can be frustrating and we can appreciate that a quick solution will be desired, the good news about these types of weeds is that they are largely shallow rooting and should come out with the first mow at the 6-8 week mark after sowing. If they don’t, they should be easy to pull out of the turf.
If you find that when the lawn is at least six months old and has been taken over by weeds or moss, you can use a Feed, Weed and Moss Killer product.
Remember that all herbicides are different and the exact time you must wait to apply weed killers to newly planted grass will vary from one product to another. Also, some herbicides cannot be applied to certain species of turfgrass. For best results, always refer to the herbicide bottle’s label.
You can control weeds in newly planted grass seed and seedlings without the use of herbicides. Manually pulling the weeds by hand when they first appear keeps them from producing seeds and prevents the problematic plants from spreading, according to the University of California Statewide Integrated Pest Management Program website. They suggest keeping the newly planted grass weed free with proper mowing, irrigation and fertilization. Since newly planted turfgrass has short roots, keep the root zone moist by watering the soil lightly. However, avoid over saturating the soil. After the turfgrass has become established, promote deep and healthy root growth by watering infrequently but deeply.
A general rule of thumb is to wait at least until you have mowed the new grass four times before using any standard postemergent broadleaf herbicide. A standard pre-emergent herbicide should not be applied until at least three to four months after seeding the area.
Weed Control after Seeding
Before you plant grass seed, you should always prepare the area by removing any weeds that may be growing in the location. Even with careful preparation of the planting site, weeds can still develop among the newly planted grass seed. Weed killers, however, can harm grass seeds and seedlings if applied too early or improperly.
Some pre-emergent herbicides can safely be used during seeding and usually come mixed with a seed starter. These products have the active ingredient Siduron – also known as Tupersan – that works by suppressing weed seeds while improving root development of the new grass. The fertilizer and pre-emergent herbicide mix is applied with a drop or rotary spreader using a rate of 2 1/2 pounds per 1,000 square feet. The spreader setting and actual application depends on the brand of starter fertilizer plus weed control you use, and you should always follow the instructions found on the label.
Weed management should be completed before seeding the lawn with a non-selective herbicide seven to 14 days before you till the soil. A second application of the herbicide may be required to kill any weeds you missed during the first treatment. Wait another seven days until tilling the soil if a second application is used.
Marylee Gowans has written about gardening for both online and print publications. She attended the University of Akron, graduating with a Master of Fine Arts in creative writing. In 2009, she received master gardener certification from the Master Gardeners of Summit County, Ohio.