Spray for weeds before seeding
Since releasing this year’s FREE Guide To Fall Seeding we have had some questions come about spraying weeds now leading up to the seeding. In and this blog post will answer those.
First off, you do NOT have to kill all the weeds. The winter is going to kill them for you and having a few here and there will not get in your way too badly. However, if you have had a big emergence of crabgrass in your lawn (where it is all you can see), you will want to try and knock that back some – mainly so it doesn’t go to seed on you.
It’s probably hard for you to tell, but this lawn here is in Munster, IN and this is 99% crabgrass.
Here is what it looks like up close:
If this is you, you will want to spray this and start knocking it down. Leaving it in there is good because it will help hold your seed in place but for sure, if your lawn is this thick with crabgrass, hose it good with quinclorac , quincept or mesotrione leading up to seeding following the recommendations below.
Note on Details:
I’m going to get highly detailed here because I respect you and your intelligence. You’re smart and therefore you can and should seek to understand these chems so you can get the proper result from using them and have no fear of them. I respect the fact that once you take the time to understand this example, you will be better at discernment of similar questions in the future and thus you will be more confident in your approach and strategy. In other words, I’m not going to talk to you like you’re dumb and just tell you what to do. Instead I’m going to teach you like a professional. I hope you are good with that.
Second, I respect the green industry and the lawn pros who make their living doing this day in and day out. When you use professional formulations of products like the ones listed here, I now view you on their level and that also means we need to stay within the bounds of the label which is the law. If you see YouTubers or social media influencers out there not following the label, including me, you should call them/me out. Everyone makes mistakes here and there, but it’s their reaction to being called out that truly shows their intent. I like to think everyone means well and is willing to admit when they are wrong.
Can I Spray Weeds and Kill Crabgrass Now if I Plan to Seed In September/Fall Time?
This is the most common question and it’s difficult to answer for all of you so I’m going to show you how to find the answer for yourself using 2 examples.
Reading The Label – Quinclorac 75DF
Key: The answer to your question is on the label. Labels of weed control products almost always tell you the wait time until seeding after application. Let’s look at two that you likely may be using.
First one is quinclorac . This is the first choice active ingredient that kills crabgrass that you may be seeing. If your lawn is covered in crabgrass like a carpet – especially through the middle or meaty part of the lawn, you will want to kill it off or at least stunt it really well before seeding.
The formulation most of you have is the “DF” which stands for “dry flowable” which means it’s small granules that you put in water to make a solution to spray. The concentration is 75% quinclorac.
Here’s the trick to reading labels fast. Find the PDF online. Make sure it is the VERY SAME product you have in hand. DoMyOwn is a great resource for this .
Once you pull up the label, hit “command F” on Mac or “control F” on PC and this opens up a search window. Type the word “Seed” in that window and it will reveal how many times that word appears in the label PDF.
Use the down arrows in that window to “scroll” through all the instances where that word appears. As I did this, I found the following very quickly.
So we can see that for certain types of seedings, this product won’t cause any harm at all but we have to scroll down to the tables 1 and 4 to get the details. Table 1 is going to tell us the grass types that are “highly” and “moderately” tolerant and table 4 will tell us the timing of the applications for ANY seeding.
This is where it sometimes gets confusing so follow along with me.
Here is Table 1
So what this is telling us is that you can use Quinclorac 75DF on established grasses listed as “highly” or “moderately” tolerant. That is really all this chart is for. It has nothing to do with seeding, hence the word “established.” But you still have to look at this chart first to find out if you should even use this product in the first place.
It’s main purpose is to tell you that you should not use this product on Bahia, Colonial Bent, Centipede or St Aug, period. Doesn’t matter if you are seeding or not, you should NOT use this product on these grass types. It also warns you about using it in or around fine fescues – they must be part of a blend if you do.
So in our case, where we are thinking about seeding the lawn, if we are planning to seed Bahia grass for example, then this product is out, 100%. No Bueno.
So if you passed the test on this part and are seeding Kentucky Bluegrass for example, then you need to next consult table 4 which is going to give you the timing of seeding both before and after.
Let’s stick with our example of Kentucky Bluegrass and you can see that it’s ok to apply quinclorac to the lawn to kill crabgrass 7 days before seeding or more. So right now, if you are let’s say 2 weeks away from seeding, you are welcome to spray away and kill that crabgrass dead. (note, this product turns crabgrass orange/red in about 6 days. But it takes much longer for the crabgrass to fully break down so likely some of it will still be there when you seed, just red and dead).
Also of note, if you have crabgrass living after or during your seed grow in, you have to wait 28 days after emergence (when you see it) before spraying. It’s important to understand what mix you are seeding in this case because if you have a tall fescue, bluegrass mixed seed , the tall fescue will emerge in about 10 days but the bluegrass won’t emerge for 18-21 days so you need to wait 28 days AFTER THE BLUEGRASS emerges before spraying quinclorac. If you really want to be safe, wait the 28 days and 1-2 mowings before applying – this adds some extra protection for the late bloomers as mowing encourages new grass to “harden off” quicker.
Reading The Label – Seeding and Tenacity – Mesotrione
( we have the generic which is cheaper FYI)I will throw this one in real quick because it’s a little different. We recommend this product for a pre-emergent application at the time of seeding. It will suppress certain weeds in your grow in. If you are new and inexperienced, DO NOT think you have to use this – your results will be ok without it. But if you do use it, people think they can just spray it anytime they want and this is not true.
You can spray it anytime you want leading up to seed day, and on seed day, but once your seeds germinate, you should NOT spray it again until the new gras has been mowed 2-4 times or 4 weeks whichever is longer.
So to be clear – you can apply this up to seeding, but once the seed germinates (4-5 days for rye, up to 21 days for bluegrass) you should NOT apply it to weeds until the new turf has been mowed 2-4 times or 4 weeks, whichever is longer. This is because baby grass is weak and can’t withstand/tolerate mesotrione .
Reading The Label – Speed Zone – Red Label
This is another weed control I have recommended heavily and they list right on the label in clear printing how long to wait until you seed. Keep in mind, this product has an 85F degree temp restriction anyway so many of you would not be using it in summer, but in case you did, here is the wait time after app before seeding:
Reading the Label – Quincept – New Farm
Ok now just as I make everything seem like it’s as simple as reading the label, NuFarm (who I love) comes in and just leaves it off their Quincept label completely . Maybe someone from NuFarm can Tweet me and let me know why y’all have left this off your label for so many years… is there a typo you have not corrected? I have read and read the label and this is all I can find – it’s all about “spraying after you seed” but nothing about “spraying before you seed.”
You can read that all you want, backward and forward and it only tells you about “after” seeding. And since I have recommended this weed control so heavily this year I feel like I need to provide an answer.
First off, when I worked for TruGreen ChemLawn, Quincept was our go-to weed control for summer and I remember that every year that right around 3 weeks before overseeding time we would get a memo telling us to cut off the Quincept use. The memo would come early but would read “stop spraying Quincept 2 weeks prior to starting your overseedings for customers.”
So that is my first clue as to the reseed window – it comes from my experience.
Next, I found a product that is similar to Quincept in that it has the same active ingredients plus one. That is Q4 Plus . It has very similar concentrations of the active ingredients within the Quincept plus one more. That product says this:
In short, if you are using Quincept, wait a minimum of 14 days after application to throw down your grass seed. I had to use some logic with this one and figured I’d share it just in case you are doing all the research and coming up empty. Now you know.
So there you go, all about reading labels for seeding – hope this has helped you and that your seeding will be successful this season!
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Controlling Weeds before You Plant Your Lawn
If you have decided that you are ready for a total lawn makeover, your first order of business should be to get rid of the weeds. Most professional landscapers will tell you that the best way to get rid of weeds is to spray the entire area with an herbicide.
The most commonly available, easiest to use, and relatively safest herbicide is one with the active ingredient glyphosate. Brand names include Roundup, Kleenup, and others. The best way to tell whether you’re getting the product you want is to ask your hardware store or garden center associate to help you. Be sure to read the label and look for the active ingredient glyphosate.
You will probably have to apply this herbicide more than once.
For a lawn over 1,000 square feet, you need to rent or buy a backpack sprayer to do the job. The herbicide comes in a concentrated form that you mix with water according to the manufacturer’s instructions.
Cordon off your lawn with tape, streamers, balloons, or some type of barrier. Keep the kids and your pets off the lawn and away from the yard. Glyphosate is a relatively benign herbicide, but it is a pesticide, and children and pets have lower sensitivity thresholds to chemicals than adults.
Make sure that you follow the label instructions and wear a long-sleeved shirt, long pants, rubber boots, and plastic gloves. Wait the specified time for the herbicide to work and then rake off any debris. Your lawn should be grass- and weed-free at this time, but be sure to make another application if you feel it is necessary.
When you’ve finally decided that all weeds and remaining grass are gone, wait one week before you plant your new expensive grass seed.
For those of you who prefer not to use toxic synthetic chemicals to kill the old grass and/or weeds, you can take several approaches to getting rid of weeds without chemicals.
Rent a tiller: For a modest-sized yard with not a lot of weeds or dense turf, till your lawn area to a depth of 4 to 8 inches, rake out the grass and weeds, and till again. Keep tilling and raking until all the green matter is gone. Dump all this material in your compost bin where it decomposes over a period of months.
Credit: “Horns & Tiller,” © 2008 , Lisa Brewster used under a Creative Commons Attribution 2.0 Generic license: http://creativecommons.org/licenses/by/2.0/legalcode
Be sure to get a tiller that has the rotating tines in the rear behind the tires. They easier to handle than the tillers with the tines in front and over the engine. Running a front-tined tiller is like trying to control a bucking bronco.
Don’t try to till dry or very wet soil. Water the whole area, let it dry for a few days, and then till.
Renting a sod cutter: You simply guide the sod cutter over your old weedy lawn, and it cuts the turf at just below soil level. Turn the sheets of grass upside down where they will decompose and add nutrients to the soil. You also can haul the sod to a recycling center that accepts yard waste.
Using black plastic: If your lawn is less than 1,000 square feet, buy enough heavy-gauge black plastic to cover your entire lawn. Spread the plastic out over the lawn and weigh down the edges with stakes, or rocks. Without sunlight, grass can’t grow and eventually dies. This process can take anywhere from a month to three months, depending on how hot and dry your season is.
Plowing: Plowing is another method to use if your lawn is rather large. Adjust the plow blade or blades to dig the soil to a depth of 6 to 8 inches. Rake off the weeds and debris and keep plowing and raking until you get rid of all the unwanted green matter.
*Bulldozing: If you have a really large area, a bulldozer or Bobcat may be a good option. Adjust the blade so that you’re just scraping off the thin layer of grass and weeds. You don’t want to take off the soil layer.
About This Article
This article is from the book:
About the book authors:
About the Authors Lance Walheim, former staff garden writer for Sunset magazine, is the nationally recognized author of over 30 widely read garden books, including The Natural Rose Gardener and Hungry Minds’ Roses For Dummies. The National Gardening Association (NGA) is recognized for its bimonthly National Gardening magazine and prolific work in science education for children. NGA is also the coauthor of Gardening For Dummies. Roses For Dummies. Perennials For Dummies. Annuals For Dummies. and Container Gardening For Dummies.
How Long After Using Weed Killer Can You Sow Seed?
It makes sense to be cautious about sowing seed after using weed killer. Certain herbicides can harm sprouting seeds and young plants. However, while you must wait several months to sow seed after applying some weed killers, you only need to wait a few days after applying others. The reason for this difference lies in the effect of the active chemicals in the individual products. Read the label carefully and follow all the directions when applying a weed killer.
Sowing Seed After Applying Glyphosate
You can sow seeds in as little as a week or even sooner after spraying glyphosate, a systemic, nonselective weed killer. Glyphosate moves from the leaves to the roots of plants, destroying the entire plant, but leaving no residue in the soil. The chemical affects many types of plants, including weeds, grasses and desirable plants, but after the liquid is absorbed into the plant, it doesn’t pose any further threat. You can safely sow ornamental flower seeds a day after spraying with glyphosate and grass and vegetable seeds, three days after, even though the herbicide takes up to seven days to destroy weeds. If you remove the dying weeds too soon, live roots could remain in the soil, ready to regrow. Another systemic weed killer that doesn’t affect seeds is pelargonic acid.
Pre-Emergence Weed Killers and Sowing Seed
Pre-emergence weed killers prevent seeds from sprouting. They create a chemical barrier on the soil surface that suppresses seed development. What this means is, if you sow your own seed after applying a pre-emergence weed killer, the seed isn’t likely to grow. However, some pre-emergence products only affect grassy weeds, so you can safely sow most vegetable and flower seeds after applying these herbicides. The same doesn’t apply to reseeding or overseeding your lawn. Grass seed won’t sprout until a pre-emergence weed killer has decayed and become ineffective. For example, it isn’t safe to sow lawn seed until four months after applying a crabgrass preventer.
Sowing seed after applying a pre-emergence weed killer disturbs the chemical barrier on the soil surface, which means that weed seeds may germinate too.
Seed Sowing and Selective Weed Killers
Many selective weed killers leave little or no trace in the soil, and they target certain plants while leaving others unharmed. Generally, these types of herbicides destroy either grassy weeds or broadleaf weeds. You can safely sow most seeds in your vegetable or flower patch a day after applying selective herbicides, such as sethoxydim, clethodim and bentazon, for grassy weeds. These herbicides only affect your desired plants if the plants belong to the grass family. For lawns, herbicides that destroy broadleaf weeds are effective, but it isn’t safe to reseed until a month after applying these products, unless the label states differently.
- National Pesticide Information Center: Can I Plant Vegetables After Using a Weed Killer?
- Oregon State University: Top 10 Reasons Your Herbicide Failed
- Scotts: The Questions People Ask Most About Grass Seed
- The Center for Agriculture, Food and the Environment
- Roundup: When can I replant/reseed after use?
- The University of Tennessee Institute of Agriculture: Common Herbicides for Fruit and Vegetable Weed Control
- Roundup: How Soon Can I Replant After Using Roundup Weed & Grass Killer Products?
- Michigan State University Extension: Get an Early Start on Vegetable Garden Weed Control
A graduate of Leeds University, Jenny Green completed Master of Arts in English literature in 1998 and has been writing about gardening and homes since 2007. Green’s work appears in SFGate, Mom.me, The Pink Plumber and many home services blogs .