Will Weed and Feed Kill Grass Seed? When to Plant and Spray Many gardeners often find themselves unsure of how long they’re supposed to wait until they can apply weed and feed to their lawns How Long After I’ve Planted Grass Seed Can I Apply Weed Killer?. 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, … How Many Days Do You Have to Wait Before Seeding After Weed & Feed?. Weed and feed fertilizers are often used in combination with seeding. Weed and feed formulations consist of two components: a herbicide to kill weeds and a fertilizer to strengthen the turf. The herbicide will weaken the grass as well as the …
Will Weed and Feed Kill Grass Seed? When to Plant and Spray
Many gardeners often find themselves unsure of how long they’re supposed to wait until they can apply weed and feed to their lawns after planting grass seed. Conversely, the issue may be how long one’s supposed to wait to plant grass seed after spraying weed and feed. For both concerns, the answer largely revolves around the type of herbicides found in different weed and feed products.
Can you put weed and feed on grass seed?
You may be having an irresistible urge to spray weed and feed on your recently overseeded turf after spotting one or two weeds sprouting on the lawn. However, the growing seedlings will not be able to survive the strength of the herbicide. If you’re planning to use a weed and feed product with a post-emergent herbicide on your growing turf, wait until the grass roots anchor deeper into the soil and the lawn is established.
Also, some weed and feed products are non-selective, pre-emergent herbicides targeted at preventing weed seeds from sprouting. As such, when they’re applied on a recently seeded lawn even before the grass seeds germinate, they’ll kill the weed seeds as well as the grass seeds.
To control weeds on lawns before the new grass is established, consider alternative measures like spot treatments. You can also manually uproot the weed plants if the infestation is still in the early stages.
Mowing also helps to control weed growth in newly-established lawns, as the grass grows stronger and crowds out more weeds. In fact, it’s advisable to refrain from spraying weed and feed on your new turf until after the third mowing. By then, the grass will be strong enough to withstand herbicides.
However, even then, you should only use a post-emergent, selective weed and feed product. These will easily kill broadleaf weeds like dandelions and clover without harming your turfgrass. Pre-emergent herbicides won’t work on already existing weed plants, while non-selective/systemic herbicides will kill both the weeds and your growing turfgrass.
When to plant grass seed after weed and feed?
The best time to plant grass seed after applying weed and feed depends on whether the weed and feed used contained a pre-emergent or post-emergent herbicide. For weed and feed products containing post-emergent, systemic weed killers, you can plant grass seed as soon as two weeks after application.
That’s because systemic herbicides don’t leave any residue in the soil that might harm seeds grown a few days after. They’re instead absorbed into plants via the leaves and roots, killing the whole plant within 7 days. Common examples of systemic herbicides include glyphosate and pelargonic acid.
Pre-emergent herbicides, on the other hand, are formulated to inhibit seed germination by forming a chemical barricade atop the soil. Thus, if you plant your grass seed soon after applying a weed and feed with a pre-emergent herbicide, they won’t sprout as the herbicide will still be in the soil.
To seed your lawn after using a pre-emergent weed and feed, you may have to wait between 1-6 months, with 2 months being the average wait time. This is due to the wide variation in the duration it takes for different types of pre-emergent herbicides to degrade in the soil. A herbicide like 2,4-D decays in as soon as four weeks, but you may have to wait for six months to plant grass seed on a lawn treated with Atrazine herbicide.
Take note, though, that there are some types of weed and feed products that can be used to suppress weed seeds without affecting grass seed. These products usually contain siduron, a pre-emergent herbicide that also boosts germination of grass seed. If your pre-emergent weed and feed contains siduron as the primary active ingredient, you can sow grass seed right after application.
Note: Always read the labelling on your weed and feed for information on how long you should wait to plant grass seed post-application. The types of herbicides infused into the product usually determines the manufacturers’ wait time recommendations.
How long after seeding can you spray for weeds?
It’s not uncommon to find weeds sprouting and growing on your lawn alongside your new grass seedlings. The right time to spray selective weed and feed on your lawn after seeding is after mowing three times. At this stage, the grass is mature enough to withstand the harsh chemical herbicides inside the weed and feed.
You can also spray a pre-emergent weed killer if the weed infestation is still in the earlier stages. When you start to notice weeds on your new turf, it’s a sign that more weed seeds are present in the ground and are about to germinate.
You should spray a pre-emergent at least 14 days after seeding, after the grass seeds have germinated into seedlings. As such, you’ll be targeting only the weed seeds that haven’t yet sprouted, and not your grass seeds.
Note: Never use a non-selective weed killer on your new lawn, no matter how mature the grass looks, as it will kill all plants it comes into contact with including the grass.
Weed Control Tips after Seeding a Lawn
You can keep weeds out of your lawn after seeding by adopting the proper watering, fertilizing, and mowing practices. Doing so helps your turf grow stronger and stay healthy enough to choke out weeds.
How Long After I’ve Planted Grass Seed Can I Apply Weed Killer?
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.
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.
Herbicides and Seeding
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 Control after Seeding
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.
Considerations and Precautions
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.
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.
How Many Days Do You Have to Wait Before Seeding After Weed & Feed?
Weed and feed fertilizers are often used in combination with seeding. Weed and feed formulations consist of two components: a herbicide to kill weeds and a fertilizer to strengthen the turf. The herbicide will weaken the grass as well as the weeds and the fertilizer will strengthen the weeds as well as the grass. When applying seed over a weed and feed application, remember that some weed and feeds can prevent grass seeds from growing.
Types of Herbicide
It’s important to know a little about herbicides so you can make the best choice for when to apply seed in an area that has been treated for weeds. The most common types of herbicide in weed and feed products are selective and systemic. Selective herbicides target a species of plant to kill while systemic herbicides work by being absorbed though the roots and then transported throughout the plant, killing it from within. Read the bag label to see what kind of herbicide is used in the weed and feed you are considering using or have used. The bag label will tell you how many days you must wait before applying seed to a lawn that has been treated with that product.
Herbicides can target weeds before they germinate from seed – pre-emergent – or as developed plants – post-emergent. Before you seed, you can use a non-selective, post-emergent herbicide to control any weeds in the area to be seeded. Most of these can be applied up to two weeks before seeding to control any existing weeds. Herbicides should not be used after seeding until the new seedlings are established. Mowing and spot treatments can be used to control weeds until the seeded area is actively growing and requires only maintenance watering. Establishment times vary depending on the type of seed you use and your weather conditions.
Using Weed and Feed
Only use a weed and feed if the weed infestation is completely uniform over the entire lawn and all species of weeds targeted will be affected by the herbicide in the weed and feed. This scenario doesn’t occur often, so it is more likely the use of an herbicide and a fertilizer separately will be needed. If the weeds are uniformly spread over the area to be treated, match the appropriate weed and feed product to your grass, the seed you have recently applied or want to apply, and the time of year.
Know What You Grow
It is important to know what kind of grass you have growing or want to have growing. Certain chemicals act differently on different species of grass and weeds. For example, the common herbicide 2,4-D is toxic to some cultivars of St. Augustine grass (Stenotaphrum secundatum), which grows in the area roughly covered by U.S. Department of Agriculture plant hardiness zones 8 through 10. Another common herbicide, atrazine, is potentially lethal to grass when applied in temperatures above 85 degrees Fahrenheit. Use the instructions on the bag of each weed and feed product to determine how it will affect seeding.
- University of Florida IFAS Extension: Weed Management in Home Lawns
- Texas Agricultural Extension Service: Maintaining St. Augustinegrass Lawns
Sara DeBerry is a graduate of the University of Florida holding a masters degree in environmental horticulture and a minor in entomology and nematology. DeBerry has been writing for government agencies since 2004 and has published peer reviewed scientific articles during her studies at UF.