Since weed and feed products are designed to prevent germination — or to eradicate a living plant — they can, for the most part, have a similar effect on young turf grass. The only exception is the pre-emergent herbicide siduron, which is actually used to assist in seed germination. When using a pre-emergent that does not contain siduron, wait a minimum of two months before seeding. If using a product designed for broadleaf weeds, read the label carefully, because the active ingredient in these post-emergent herbicides have a wider range for the waiting period. Grass can be planted in as little as one month after application for products using 2,4-D to as much as six months for atrazine-based products.
Weed and feed products consist of fertilizers such as nitrogen or potassium, and a pre-emergent or post-emergent herbicide. If the weed and feed is designed for spring application, it contains a pre-emergent. If it is designed for later in the growing season, it incorporates a post-emergent herbicide. Knowing which one you are using is important because the herbicides affect plants in significantly different ways.
Pre-emergent weed and feed is applied in early spring so the herbicide is in place before the undesirable weeds germinate. Pre-emergent herbicide works by inhibiting germination. It must be watered with at least one-half inch of water to move the chemical from the surface into the soil. Post-emergent herbicides, however, must be applied while the weeds are actively growing because for the chemical to work, the herbicide must be absorbed into the plant.
Why You Wait
You want a beautiful lawn for your family to enjoy, but it’s no longer enough to just mow it. You have to fertilize, water, kill weeds and then reseed any bare spots. Using a weed and feed product saved you some time, so now you’re ready to plant some grass seed. You may have to wait a bit longer, though, depending on the type of weed and feed product you used.
When you are ready to seed your lawn, use a garden rake to remove debris and to break up the surface to ensure the seed comes into contact with the soil. Broadcast the seeds in two directions to ensure complete coverage, and water the ground lightly and often for up to two weeks — keeping the soil moist. Once seedlings have established, gradually reduce the frequency of the watering, but lengthen the amount of time per watering. This will encourage a deep root system for your grass.
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.
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.
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.
Using Weed and Feed
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.
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.
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.
This is a big question in early spring: “My lawn needs everything what should I do first, put down seed or kill my weeds? The reason why this question is tricky is because many of the weed controls will harm new grass seedlings.
Answer: If you have more than 75% grass, you may be surprised how your good grass will fill in with four feedings a year at 6 to 8 week intervals. With this option you skip spring seeding (you can always seed in fall if your lawn still needs it). Here is a schedule for the year: Feed your lawn now with Scotts Turf Builder with Halts Crabgrass Preventer. In 6 to 8 weeks after your first feeding, feed again with Scotts Turf Builder Weed and Feed if you have lots of weeds or if you only have a few weeds, your second feeding can be Turf Builder Lawn Food and spot treat your weeds with Ortho Weed B Gon MAX plus Crabgrass Killer OR Roundup For Lawns. Put down Scotts GrubEx sometime in May or June. In 6 to 8 weeks after your second feeding, feed again with Scotts Turf Builder with SummerGuard to control insects. In 6 to 8 weeks after your third feeding, in late summer/early fall, feed with Turf Builder Lawn Food.
Here are your best two options:
Do you have less than 75% good grass with bare spots larger than a few inches in diameter?
Answer: If lots of larger spots, then seed this spring. Be sure to use a special Starter Lawn Food plus Weed Preventer that is compatible with grass seed (the regular crabgrass preventers will keep grass seed from growing). If you do not prevent weeds when you seed, you are likely to be very disappointed as crabgrass and other weeds will germinate and choke out your good grass before it has a chance to take hold. A machine called a slit-seeder will help make sure the grass seed comes in contact with the soil. You just select the Turf Builder Grass Seed blend that is right for your conditions, such as sun, shade, heat-tolerant, etc. If you only have a few bare spots to take care of, consider Scotts EZ Seed. I think this is the best bare spot repair product we have ever sold! Spread the Starter Lawn Food plus Weed Preventer after you put down the seed. Feed your lawn again in one month after seeding with Turf Builder Lawn Food. Once your new grass has been mowed 4 times, you can kill weeds with Ortho Weed B Gon MAX plus Crabgrass Killer OR Roundup For Lawns.