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.
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.
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.
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.
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.
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.
How They Work
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.
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.
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.
If you must sow grass seed after applying weed and feed, wait for at least four to six weeks before doing so to ensure the herbicide won’t prevent the seeds from sprouting. Prepare seedbeds with the help of a rake which is one of the important garden tools that every gardener should have. It helps the seeds to have proper contact with the ground and prevents any bare patches.
In order to activate, most weed and feed products are granular and should be applied to moist grass. Mow 2 – 4 days in advance and use the weed and feed products for best results, without additional rain for at least 48 hours. After application, do not mow the treated grass for at least 7 days to allow the herbicide time to work.
Weed and feed products work by preventing new growth, effectively stopping weed seeds from sprouting and newly sprouted wheat from flourishing. However, the herbicides used are insufficient to target weeds only; grass grains and any new grass growth are the same.
Hindering New Growth
Weed and feed products, as the name implies, contain both a fertilizer and a herbicide to control weeds while feeding the surrounding grass. If the lawn has grass that is already established, this works well. The product should ideally be applied just a couple of weeks after the final frost when grass and weeds grow visibly because it is not effective for sleeping weeds. Apply it periodically throughout the rest of the year as well to keep weeds under control.
A plan weed and feed product to your lawn may seem like a perfect way to kill two birds with one stone. Not only are you can to get eliminate irritating weeds however the chemical contained within the product additionally can facilitate the grass to thrive. Weed and feed products aren’t ideal for all situations though and may cause some problems if you plan to receive the lawn soon after their application.
It can take up to four weeks for the herbicide effective to fade, so sowing grass soon after applying weed and feed is likely futile because new grass won’t be able to grow.
Ideally, you should plant seeds well enough before frost in the autumn so that the new grass will grow for several weeks before sleep. You can also sow grass seed in the early spring, though if you do so you should hold off on applying weaving feet for at least four to eight weeks to ensure it doesn’t damage the young grass.