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.
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.
Why You Wait
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.
We put down Scotts Weed & Feed on 4/21/13, following the instructins to first wet the grass and used a spreader. BUT! We didnt realize we couldnt seed AFTER- Scotts states minimum of 4 weeks listed on the product.
Also when you decide to seed in the future Scott’s sells a VERY good product called Scott’s Step 1. It is much more expensive (I think back when I used it was somewhere between $50-60 for a small 10lb bag) than their normal line of products and you may have to go to a specialty store if your big box stores don’t carry it. This is MEANT to be applied at seeding as it has a selective herbicide that prevents weeds from sprouting but allows (most) grass seed to sprout, while also giving a feeding to the new grass.
You can keep trying every couple of weeks and not need to rake up the “dead” seed so no worry of overseeding as if grass does take it will eventually get the nutrients from the decomposing seed and will also supply a bit of water retention properties when watered.
I think it is less likely that you get growth and then the young grass dies as the roots go deeper, more likely is you won’t get growth at all or significantly less than you had planned for (say 1/4 or 1/3 germination rate, btw totally just throwing a random number out since I have no idea if anyone could give a good estimation).
Thanks for your replies. What I have been wondering is, what is the “worst case scenario”, if I do plant seed in 2-4 weeks? If the herbicide is still strong and the seeds will not germinate, are those seeds “dead” or will they germinate when the time is right? Or are they contaminated and then I wait a few weeks and reseed again? Or, what if they germinate and grow, but then die later? Could I/should I reseed after boh scenarios or would I need to remove all the old seed and start over? I don’t want to overseed.