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.
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.
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
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.
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.
This duration varies according to the amount of moisture that has been received, also the temperature range and the type of soil, and even different varieties of weeds which awaken at different times.
Then try a small test plot first. That will keep you in check so you don’t lose the investment of your seed, your financial investment, and your labor, if the preventer is still preventing.
You want to get one with the active ingredient “dithiopyr”, usually found under the trade name “Dimension”.
QUESTION 3: Can I Apply Pre Emergent,
then Lay New Sod?
All preemergents emphasize that you get maximum protection against weed development when that barrier zone remains undisturbed. Any disruption of that barrier (any cultivation of the ground) can furnish a ‘chemical-free’ path for some sprouts to pass through to the surface without getting zinged.
For this reason, you could do this project without using a pre emergent herbicide.
I live in Kentucky and last year I power seeded my yard but I think that I was a bit too late. I did get some success, but want to know what is the best time to get a pre-emergent down? I don’t want to miss this window and I desperately want to apply it at the very very best time.
If this is your intent, then go ahead. Just remember that you must make concessions for the young grass that would not be a concern for gardeners treating a well-established existing lawn.
The waiting time for seeding after crabgrass preventer depends on what type of product is used. Crabgrass pre-emergents may have different ingredients that require longer waiting periods before reseeding can commence. If the grass is planted too soon afterward, the grass will not grow. Waiting times depend on the chemicals in the pre-emergent; for example, if it has bensulide, it may take up to four months before reseeding is recommended.
Crabgrass post-emergent herbicides are different than pre-emergents because they are applied to crabgrass that is already visible. These post-emergents are made with glyphosate and are mixed at a ratio of 2/3 ounces for every gallon of water for crabgrass less than 6 inches high. This ratio increases if the crabgrass is taller. Seeding after crabgrass preventer is applied is similar to seeding after pre-emergents, and lawns can be reseeded one week after the glyphosate is applied. If you are unsure, read the instructions on the packaging since some manufacturers may have different directions.
Before applying pre-emergent and new grass seed, it is essential to keep in mind that the seeding must be completed no less than 45 days before the average first fall frost. Once some pre-emergents are applied, you only have to wait seven to 10 days before reseeding. The same is true of laying sod after pre-emergent.
Seeding After Pre-emergent
Dimension pre-emergent herbicides work on crabgrass and other weeds. If you are planning on seeding after using a Dimension product, be sure to read the directions. Coverage, mixing ratios and waiting times will vary depending on the type of weed prevention product purchased as well as the weather where you are located and the state of your lawn.
Lawns that are looking dry, diseased or spotty can benefit from reseeding after pre-emergents are applied. Species of grass that benefit most from this include tall and fine fescue, ryegrass and bluegrass. If the grass is seriously damaged, it may be better to start over instead of reseeding, though.
Seeding after pre-emergent is one of the most important ways to stop weeds from overtaking a lawn. Do-It-Yourself Pest Control explains that these herbicides are made from chemicals that target weeds so they will not sprout in the first place. Understanding how and when to apply it and knowing the best approach to planting grass after pre-emergent will help keep your lawn green and healthy. Remember that pre-emergents are not for visible weeds; post-emergents are used for that.
Reseeding can strengthen a lawn, making it look fuller and greener. It can also save money in the long run, as the grass will be sturdier and will respond better to watering, fertilizing and mowing. Reseeded lawns may also have a better chance against foot traffic, diseases and insects. Lawns normally adapt best to reseeding during the early fall and later summer. This gives the lawn several months to take root and thrive before lower temperatures set in.