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 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.
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.
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.
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.
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.
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.
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.
In short, here’s what you should do if you encounter weeds in your newly seeded lawn:
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.
Always read product labels thoroughly and follow instructions, including specific guidance for your grass type.
Starter fertilizers help your new seed or sod get started right.
Between June and August, proper feeding helps strengthen lawns against heat and drought. Keep your lawn beautiful and resilient with Pennington UltraGreen Lawn Fertilizer 30-0-4. This premium lawn fertilizer, ideal for northern or southern lawns, keeps feeding for up to three months. Your lawn gets essential nutrients, including iron for rich color, and you get thick, lush green grass.
Part 4 – Late Summer to Late Fall
On top of weed control, Pennington UltraGreen Crabgrass Preventer Plus Fertilizer III 30-0-4 delivers iron and fast-acting nitrogen for immediate greening, and slow-release nitrogen for extended feeding for up to three months. Always follow the label instructions for your specific grass type. Do not apply this product within 60 days of overseeding. Wait until the following year before treating new sod.
Always check the label for your specific grass type, then follow instructions accordingly. Used as directed, you can apply Pennington UltraGreen Lawn Fertilizer 30-0-4 to wet or dry lawns and not worry about fertilizer burn.
To keep your existing lawn looking its best year-round, choose a fertilizer plan that meets its changing seasonal needs. At Pennington, we make it simple for northern and southern lawns. Just follow our four-part annual lawn fertilizer program:
If you plan to overseed, avoid weed & feed for four weeks before. After overseeding, wait until your third mowing occurs. For sodding, sprigging or plugging, wait four weeks before you weed & feed so new grass can start without delay.