Learn how to kill weed seeds in soil to prevent weeds and other invasive grasses from continuing to sprout every year. Get your FREE Guide To Fall Seeding from the Lawn Care Nut featuring questions and answers about spraying weeds leading up to the seeding, you do NOT have to kill all the weeds at once and more now! From April SportsTurf “Q&A with Pamela Sherratt: Q: We are getting ready to overseed our soccer field this spring. What weed control options are there? A: Successfully growing cool-season turf from seed in the spring can be a challenge because the weed pressure is so great, which is one if the reasons why the recommended
How to Kill Weed Seeds in Soil [5 Easy Methods]
To kill weed seeds in soil you will have to apply one or more of the following methods:
- Heat soil to temperatures high enough to kill weeds seeds
- Force seeds to sprout and destroy growing weeds
- Apply chemical or natural weed killers that prevent weeds from sprouting
- Use flame weeding to destroy weeds and seeds at once
- Layer mulch in garden areas to suppress weed sprouting and attract insects that eat seeds
With this arsenal of tricks for killing weed seeds before they sprout, you can stop the spread of weeds in both your lawn and garden.
Table of Contents
5 Tips for Killing Weed Seeds
Rather than spending time and effort battling weeds as they sprout, attack weeds at the source by killing weed seeds. Each of these methods destroys weed seeds, which ensures you won’t have to battle recurring weed invasions. Try these ways to get rid of weed seeds yourself.
Soil solarization is a very powerful method for killing weed seeds. Weed seeds begin to die if soil temperatures surpass 108 degrees, with full seed death ensured by soil surface temperatures of 140 degrees or more. Solarization uses clear plastic tarps to trap heat at the soil surface, killing weed seeds within the tarped area. To solarize an area, follow these steps:
- Clear the area of all vegetation through use of a hoe or other garden implement. Remove any woody stumps
- Till the soil to further break up any weed root systems left behind.
- Rake away all vegetation residue
- Water the tilled and cleared soil with a garden hose until it is damp.
- Lay a sheet of clear plastic over the area. Weigh it down tightly at the edges
- Leave the plastic in place for at least two months.
Solarization is the best method to reclaim a weedy garden or other area. It is a “clean slate” for your soil, because seeds will be destroyed by the solar heat trapped beneath the plastic.
It is typically tough to implement solarization in large areas and is not usually suitable for use in lawns, where you may want to preserve grass or other plants. Pre-emergent weed killers and flame weeding are much better for use in lawns.
Till and Kill
Weed seeds can lie dormant in soil for decades and are only “activated” when brought to within an inch of the surface. One method to rid soil of dormant weed seeds is to force these dormant seeds to sprout, then attack them with a powerful natural or chemical weed killer. To do this:
- In spring, till the affected area. Tilling brings dormant seeds to the surface
- Water the area for 1–2 weeks with a sprinkler or soaker hose
- When weeds begin to sprout, apply the weed killer of your choice
This is another “clean slate” method, where you force weed seeds to show themselves and then kill young weeds before they mature and cast seeds. Because of the invasive tilling step, it is not best used in areas with desirable grasses and plants.
Use Pre-Emergent Weed Killer
Pre-emergent weed killer stops weeds in their tracks. It works by attacking weed seeds just as they begin to germinate, killing them before they even poke above the surface. It’s a weed killer so good, the only sign it’s working is that there will be no new weeds at all.
Weed Control Seed
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!
Welcome to the official site of Allyn Hane, The Lawn Care Nut from YouTube. Here you will find my free newsletter that gives you much more than just the tip. I also carry the full line of N-Ext soil optimization products including RGS, Air8 and De-Thatch along with MicroGreen and Green Effect plus much more!
Weed control during spring seeding
From April SportsTurf “Q&A with Pamela Sherratt:
Q: We are getting ready to overseed our soccer field this spring. What weed control options are there?
A: Successfully growing cool-season turf from seed in the spring can be a challenge because the weed pressure is so great, which is one if the reasons why the recommended time to do renovation is in the fall. In the real world however, athletic fields are in a constant state of renovation and so seeding is a season-long operation.
Weeds that emerge in spring, like crabgrass, prostrate knotweed, yellow nutsedge, goosegrass and annual bluegrass are particularly troublesome on athletic fields because they can germinate and establish quickly, even on compacted soils. Weed seed present in the soil is laying dormant just waiting for an opportunity under the right environmental and cultural conditions to invade a weakened turf with bare soil. Because weed pressure is so great in the spring and early summer months, it is important that the soil is not disturbed (avoid tilling as this will bring up weed seeds) and that the seedbed be treated with an herbicide that does not adversely affect germination of the desired grass seed.
There are several approaches to using an herbicide during the seed establishment period. Following is a summary of those options, based on years of herbicide trial work by Dr. Dave Gardner. One strategy is to seed in early spring and then after the seedling turf has established, apply an herbicide with pre and early postemergence activity, such as dithiopyr (Dimension, others*). This strategy requires very careful timing, and on most athletic surfaces, overseeding is not a once per year operation. Once the application of dithiopyr is made, as is the case with most preemergence herbicides, future overseeding operations must be delayed according to the label.
In fact, on areas that you plan on seeding or over-seeding in late spring or summer, hopefully you did not apply a preemergence herbicide. If you did, then be aware that almost all of the preemergence herbicides on the market are very effective at controlling not only weed seedlings, but also the seedlings of our desired turfgrasses. Fortunately, there are three preemergence herbicides that are labeled for use at seeding time: siduron (Tupersan), mesotrione (Tenacity), and topramazone (Pylex).
Siduron has been available for use in turf for many years. It is safe for use on seedling turf. Follow the label directions carefully. When used properly, siduron will reduce crabgrass, goosegrass, foxtail, and many summer annual broadleaf weeds by about 80%.
Mesotrione is in a unique class of chemistry and this product has a very diverse label, including pre- and postemergence control of both broadleaf weeds and annual grasses. It also controls sedges preemergence and certain perennial weedy grasses postemergence. One of its key uses is the preemergence control of annual grassy and broadleaf weeds in newly seeded turfgrass. When used as directed, mesotrione will result in nearly complete control of crabgrass, goosegrass, foxtail, and many summer annual broadleaf weeds. But, it will not affect the growth and development of the seedling turf. Most effective use of this product is to apply it to the soil surface right after the seeds have been raked in but before mulch is applied.
You can then begin to irrigate as you normally would to establish seedling turfgrass. Mesotrione is very safe to seedling turf. However, some phytotoxicity has been reported if it is applied to young turfgrass seedlings. If you are using multiple applications of mesotrione as part of a program to control stubborn weeds, such as creeping bentgrass, then you want to avoid overseeding or reseeding the area until you are making your last mesotrione application. In other words, it is better to wait and reseed with the second or third mesotrione application, then to seed when the first round of mesotrione is being applied.
Topramazone is a more recent introduction to the turfgrass market. It is similar to mesotrione in its weed control spectrum and its safety to seedling turfgrass. Make sure to follow the label recommendations carefully.
After the seed has germinated there is a period of time in which your options for weed control become limited. Most postemergence herbicides for broadleaf weed control have language on the label that states that following seeding, the turf needs to be sufficiently established so that it has been mowed three times before the product can be safely used.
All of the herbicides mentioned in this column are good products and can be quite effective. You can help to improve your chances of success by avoiding the 2-4 week period each year that is the peak of germination for the particular weed species that dominate your fields. For example, each of these products is quite effective at reducing weed establishment when seeding or over-seeding in July when weed competition begins to drop off. However, each of these products can produce less than complete weed control if used in mid to late May. This is more likely to be a problem if the May timing is in conjunction with seeding a slower to germinate species such as Kentucky bluegrass. By simply waiting a couple of weeks (or seeding a couple of weeks earlier), weed seed competition may be greatly reduced, which further increases your chances of success when seeding or overseeding.
*Mention of a specific product does not constitute an endorsement over other products that may be similar