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.
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.
Herbicides and Seeding
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.
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.
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.
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.
I just sprayed today, and it’s supposed to rain in 2 days (and a few days in a row). I was hoping I could toss down the grass seed tomorrow before rain, but I wasn’t sure if that’s too soon, or if it matters with this particular chemical.
I’m not concerned about getting it perfect. If 10% of the seed I put down comes up and starts to spread over the years, I’d consider that a win. Every amount above that certainly welcome, but.
Can I over-plant grass seed a day after spraying Ortho Weed B Gon? If not, how long do I need to wait (and why)?
When fighting grassy weeds, you must wait a little longer to plant your grass seed, whether you’re seeding your entire lawn, overseeding or treating bare patches. With the Weed B Gone Plus Crabgrass Control, wait at least four weeks to plant seed. Because this is specially formulated to stop grassy weed seeds from germinating, it also can stop your regular grass seed from growing.
How long you must wait to plant grass seed after treating your lawn with a Scotts Weed B Gon product depends on which product you use. When fighting broadleaf weeds such as dandelions with the basic Weed B Gon weed killer, wait at least three weeks to sow your grass seed. This product specifically targets the seeds of broadleaf weeds, but it can stop or slow down your grass seed’s germination as well.
Keeping your lawn weed-free is a constant battle that uses cultural practices, such as deep waterings, to encourage grass to choke out weeds, as well as chemical products, such as using Weed B Gon, to kill weeds before they start. These chemicals often kill grass seed as well, keeping it from germinating along with the weed seeds, so wait before you sow your seed.
With Crabgrass Preventer
Although you can’t spread grass seed at the same time you spray your lawn with Weed B Gon, other options exist to treat your lawn for weeds at the same time you plant seed. These typically come in the form of weed and feed products that offer fertilizer along with the herbicide. Look for products specifically designed to be spread with grass seed, often noted on the label as a starter fertilizer plus weed control.
When you’ve already planted your grass seed and want to apply a pre-emergent herbicide to keep weeds from competing with your new grass for water and nutrients, have a little patience. Applying a weed-control product such as Weed B Gon too soon can kill young grass. Instead, wait until you’ve mowed the new grass at least three times before using herbicides on your lawn.