Pre Emergents and Seeding

There’s a pre emergent herbicide that you can apply to your lawn that will prevent weeds from growing without preventing grass seed from growing.

Crabgrass preventer, weed preventer, Step 1, whatever you want to call it,  these early season lawn treatments are called pre emergents. Pre emergents work by creating a chemical layer in the top portion of your lawn that will kill seedlings in the period from when they begin to germinate up to right before they emerge from the surface of our lawn.  Pre emergents prevent a long list of broadleaf weeds, and grassy weeds from taking over your lawn. The most commonly talked about and perhaps the biggest nuisance of them all is crabgrass. As people begin their lawn programs every year, it’s very common to start the season off by applying a pre emergent which will provide you with several months of protection from any new weeds that germinate in your soil.

Commonplace belief is that when applying a pre emergent to your lawn, you cannot apply grass seed at the same time since the pre emergents will block the grass seed from growing. That is why homeowners are left with a decision that can be difficult sometimes, especially in early spring…”Do I apply a pre emergent or skip it so I can apply seed instead?”

Before you make this tough choice, there is actually one pre emergent that you can put down that will prevent weeds from growing without blocking your grass from growing. That’s right, there is one exception to the no seeding when applying a pre emergent rule and that exception comes from a compound called Mesotrione. Mesotrione is the active ingredient found in a few different products (I’ll recommend these products below). You can apply Mesotrione at the same time as seeding.

Now, before you celebrate prematurely, I need to tell you that of course if something sounds too good to be true then it usually is. And that’s a bit of the case with Mesotrione.

Unlike some of the best pre emergents such as Prodiamine, Dithiopyr, and Pendimethalin which last several months in your soil, Mesotrione is effective for a much shorter timeframe. Mesotrione will provide you with about 21-30 days of protection from weeds. It’s also important to point out that while yes you can apply Mesotrione to a newly seeded lawn, you can’t apply it to grass that is new. The same is true for other pre emergents. So if you’re thinking you’ll just apply another round of Mesotrione, or some other pre emergent after the Mesotrione wears off in 21-30 days, you could end up doing a lot of damage instead. Prodiamine for example states that you have to wait over 60 days once grass is established or after you’ve mowed your new grass twice (which ever is greater) before applying pre emergent.

So, what does this ultimately mean? It’s pretty simple really. If you decide you need to do some seeding but also want some protection against new weeds from growing, then by all means apply Mesotrione at the same time of seeding. At least you’ll have 21-30 days of protection. In fact by then, your lawn should be growing in pretty nicely depending on the grass type. This 21-30 day protection gives your new lawn a great head start and while the protection will eventually run out it is certainly better than nothing. Once that new grass is established and you’ve mowed it a couple of times you can safely throw down a product like Prodiamine and get several months of protection moving forward.

What’s Your Situation

Situations Where I would Not Use Mesotrione As a Pre Emergent…

1. Your Happy With Your Lawn

If things are looking good then there is no need to seed and therefor no need to use Mesotrione as a pre emergent.  Just stick to your lawn care plan which should include one of the more dominant pre emergents (prodiamine, Dithiopyr, Pendimethalin).

2. Lawn Is Just Overall Thin and Weak

Overall, spring seeding should be avoided whenever possible. The best strategy for your thin, weak lawn is to block weeds in the spring with pre emergents that are longer lasting than Mesotrione, stick to a solid lawn care program, and mow your lawn the correct way.

If you’re just starting out and your lawn has been neglected, you’ll be shocked at how a good lawn care plan and regular mowing will make a difference. I’ve improved so many neglected lawns just by blocking weed growth, applying fertilizers, and maintaining them.

3. Only Small Sections of Lawn Require Seeding

You may just have some specific areas of your lawn that need to be reseeded. If this is the case you can just choose to skip over them when applying one of the superior pre emergents and seed those areas that need to be seeded. This will leave the rest of your lawn protected except for the areas you wish to seed.

4. Weed Pressure Is Low Where You Are Seeding

If you don’t have a history of crabgrass or other weeds in your lawn then don’t worry about weeds taking over when trying to grow new grass.

Situations When I Would Use Mesotrione As a Pre Emergent

1. There’s Not Enough Grass to Make Improvements

As much as I push for people to fertilize and maintain their existing lawn to try and turn things around, there is a point where it becomes hopeless. If your lawn is completely overrun with weeds and there is little desirable grass then spending the year feeding it and maintaining it is really just a waste of money if there’s no chance in establishing your desirable turf. If this is the case then by all means pull the trigger on a spring lawn renovation which includes seeding. Core aeration, top dressing, and dethatching, are all great to do right before seeding. This provides good seed to soil contact and will improve germination rates. Applying Meostrione right on top of the seed after it is spread will give you a window of protection and allow your grass seed to get a head start on any weed seeds.

2. Large Sections Need to Be Repaired

If large sections of your lawn need to be repaired in spring, and you’ve had decent weed pressure in the past then consider applying Mesotrione when seeding these areas.

3. Areas Along Hardscaped Surfaces Need Repair

Areas along hardscaped surfaces are extra vulnerable. Soil quality isn’t best in these areas, and the extra heat from the refection of the hardcaped surface makes it the perfect place for crabgrass to thrive. Whenever I’m repairing snow plow damage along my driveway I spray Mesotrione in the areas that I seed.

Recommended Pre Emergent Products When Seeding

1. Meso 4 SC

Meso 4 SC is a unique herbicide that can be used as both a pre emergent and post emergent. It is the brand alternative to Tenacity. This 8 ounce bottle is a concentrate that gets mixed with water in a tank sprayer. 2 gallon pump srayers are great for spot spraying smaller yards, or you can use a 4 gallon battery operated sprayer which is great for blanket spraying over the entire yard.

-As a pre emergent, you can spray this product anytime before seeding or at the same time as seeding. In fact you can spray it right over your seed. After applying, water it in so it gets into the soil. Do not apply to new grass until you have mowed it at least twice.

-As a post emergent you can apply this anytime before or during seeding, or as needed to control weeds throughout the year. Just don’t apply to new grass until you have mowed it at least twice. Mix a little non ionic surfactant in your tank sprayer to get the herbicide to stick to the leaves of the plant. Don’t water in after applying.

2. Scotts Triple Action Built For Seeding 21-22-4

First off, a warning before buying this product. Make sure it says the words ‘Built For Seeding’ on the label. Scotts has another Triple Action product that cannot be used during seeding and the packaging looks very similar. To be sure, check the active ingredients and make sure you see Mesotrione listed. This is how you can be sure that it is good to use when seeding.

This product is in granular form and goes into a lawn spreader and gets distributed over your lawn. This 17 lb. bag covers 4,000 s/f. Do not apply a starter fertilizer when applying this product since it already is a fertilizer with 21% nitrogen, 22% phosphorus, and 4% Potassium. This product will prevent lawn weeds from emerging while your does, and it will also feed your lawn wherever it is applied. Water in after application. Apply this product at the same time as seeding but do not apply it to new grass.

Applying Mesotrione As a Post Emergent

It’s important to point out that Mesotrione isn’t only used as a pre emergent. In fact it’s main use, and superior use, is as a post emergent herbicide. A post emergent herbicide kills existing weeds that are already established. For post emergent herbicides I strongly recommend liquid products instead of granular. Liquid products get sprayed onto the leaves of the weeds and do a much better job of sticking then granular products. So for using Mesotrione as a post emergent I highly recommend product 1 listed in the section above.

What’s great about using Mesotrione as a post emergent herbicide is the fact that unlike other post emergent herbicides, you can use it prior to, or at the same time as seeding. Other post emergents interfere with seed germination and recommend you wait several weeks after spraying to apply seed. This makes Mesotrione the preferred lawn safe weed killer leading up to your lawn renovation which involves seeding.

Whenever I’m renovating a lawn plagued by weeds, it’s important to start by killing the weeds as best as you can leading up to your renovation. If a lawn is covered in weeds, I’ll blanket spray the entire lawn four weeks before the renovation, then again two weeks later, and then sometimes I’ll spray again the day of seeding. The only thing that’s important to remember is that when using Mesotrione as a post emergent you don’t want to immediately water your lawn. Instead you want to let it sit on the leaves for several hours, so don’t water immediately after installation and make sure there’s no rain in the forecast. This is opposite from when it’s applied as a pre emergent and needs to be watered into the soil.

Overall, Mesotrione is one of the best products to have on hand for both its pre emergent and post emergent uses, especially when seeding.

Caution

Always read the Mesotrione label before applying. As stated on the label, if you are seeding your lawn with a mix that contains more then 20% fine fescue you should not apply. Also, Mesotrione isn’t a good choice for many warm season grasses including Bermuda and Zoysia.

Pro Tips

• If using Mesotrione in liquid form, as a Post Emergent Herbicide, then adding a little Non Ionic Surfactant will help the herbicide stick to the weed leaves. Do not use a surfactant if using as a Pre Emergent Herbicide.
• Water in Mesotrione if using as a Pre Emergent Herbicide. Do not water in if using as a Post Emergent.
• Always check the label to make sure Mesotrione is safe for use on your lawn.

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