#25- Pre-Emergents

As spring rolls around, you'll see plenty of people putting down pre-emergents on their lawns and beds. Is this a good idea? We'll talk about what pre-emergents are, how they work, and some of the common misconceptions people have about them. We'll also discuss some of the different types of pre-emergents that are available, and talk about how and when to put them down, and some different approaches to using them effectively.


Hey, Hey, what is up everyone? This is Ete with another episode of Eco Lawn Science. Hope you're having a great day. Today, I want to talk a little bit about pre-emergents. As this is a time of year where that conversation gets going and you'll see over the next few weeks in the areas that the snow is melted, the temps are starting to rise a little bit, you'll see guys out there, a hundred miles an hour, dropping pre-emergents on your lawns or your neighbor's lawns. I've always found pre-emergents to be an interesting discussion. They've been around in the industry forever. There's a lot of, I would say myths or, I don't know if there's a better word than myths. There's a lot of things about them. There's a lot of information you can get and I don't know, I kind of want to challenge it. I don't know how accurate some of it is.

And so anyway, I kind of wanted to have that discussion because you'll see that happening very shortly with the pre-emergents. Here's the basic concept: you put this down on your lawn or in your flower beds, it's a granular product. There are liquid versions, but we're going to talk about granular today, but you would apply it, but after the snow melts. Once the ground just starts to warm up, the idea is you want to get it down before the ground temperature, not the air ambient temperature, the ground temperature, is about 55 degrees. According to the label, once it hits it about that point, you've kind of missed your window and so you can't go too early, there's snow on the ground. For example, here in Salt Lake, it's just about melted. It's February, I don't know, 18th, 20th. I guess I should know that.

But it's the end of February, the snow is almost melted everywhere in the Salt Lake area but it's still pretty chilly. We're having daily temperatures of 30, 40 so the ground is still, I think it's still in the 20s somewhere like that. I checked it a few weeks ago. So we're still not in time, but it's a short window because the snow will melt. It'll start to warm up and you want to get it down before that ground temperature hits 55. So before spring really gets kicking is when you want it down, is what they're recommending to put the pre-emergent down in the lawn. And so the idea is you put this down before the lawns even fully wake and as things wake up, it's going to prevent a barrier. So it gets broken down by the soil microbes and some by moisture it just depends on the product you're using, rain, snow, et cetera.

And as the granulars get broken down, they wash into the soil, they put down a barrier. So picture one of those weed mat barriers. It's kind of a different version of that. It creates a barrier, and the idea is as seeds begin to open up and germinate, they get stopped. They hit that barrier that we've applied and they can't get past it. It does not kill seeds. It does not kill weeds that are already germinated. So if you have broadleaf weeds in your lawn, when the lawn wakes up from last fall, if you have thistle, dandelion, whatever it is, this will not kill it. But it will help to minimize the germination and growth of seeds in your seed bank that have not yet germinated. So the idea is you want to get this down before they start to germinate.

So just one last time, they don't do anything for current weeds that are above the soil. They don't kill seeds. All they do is they prevent those seeds that haven't yet germinated before the temps hit 55. If you get it down then, it's going to make it difficult for those seeds to pop through. Because weed or crabgrass needs to pop through the soil layer. So the idea is you're minimizing what's going to happen. You're being preventative. It's why it's called a pre-emergent. A post-emergent is a weed control that you apply on a weed that's already alive and active and you kill the weed. Pre-emergent is you're trying to stop that germination process, you're trying to inhibit its growth before it even gets up past the soil. So a little bit about the seed bank. What that means is, picture your lawn and then picture the soil below it and down in that lower, so below the lawn in that soil, there's a seed bank and what that is is, seeds can transfer anyway, anyhow, right?

Examples of spraying are dandelions, they go yellow, then they go white and they blow away. Well, wherever they land, they're going to end up in the seed bank, right? At some point somewhere. So it could be 10 houses down, it could be a block down, it could be across town. Depends on the wind, the rain, et cetera. And so they land into your area and those seeds are now into your seed bank. These seeds have not yet popped, they haven't germinated, but they're down there. They're in a bank. So you have to be mindful and realize that that's always happening. Even if you have a nice, thick lawn and it's healthy and you don't have any weeds, you still could next year because your neighbors' could blow in, head into your seed bank and then germinate later.

The crazy part is different weeds germinate at different times. Some weeds are viable, meaning that seed is alive for 10, 20 years. So, no lie, a seed from 1980 could have landed in my lawn and sit there until the year 2000 and then one day, decide, I'm coming up. So because of this, the seed bank is always having new seeds from different types of weeds blowing in however they get there, that's why people do the pre-emergent as to prevent the seed bank from really germinating and causing damage. But depending on the weed, it depends on how long that weed can be viable or can stay alive in the ground ungerminated. Or as timing goes, that's one of the hardest things about pre-emergents. Many of the traditional pre-emergents breakdown by the microbe activity. So think about that in the winter and the summer, the two extremes, the microbes are not active, they're dormant or they're just less active.

And so if you apply that, it's just going to sit there until temperatures warm that soil temperature and the microbes get going and they start breaking down. That's when it's going to begin impact. If you think about that, I think spring and fall are the ideal times to apply any type of pre-emergent, when you have decent weather, not too cold, not too hot. Putting it down in July, it's not going to do anything. It's just going to sit there until September. So timing is a big key part in pre-emergents. But again, the biggest thing they say on the labels is you got to stay by that 55 degree temperature in the ground. There are other pre-emergents that break down by moisture. So snow, rain, that will break it down. And there are some that break down by a combination of moisture and microbes.

So you really have to understand the label of the product. I'm going to talk in a second about the different types of products. I'm just going to talk about four different ones. But there's a whole ton like everything else. And so overall, I just want to set the expectations, a pre-emergent doesn't mean if you put it down, you're not going to have weeds, you're not going to have crabgrass. It just means that if you've done it right, and there's a lot of variables to get it right. That's the hard part. Timing, if you've done everything right, timing application, you can minimize and help to suppress the amount of weeds or crabgrass that come up. But just because you put it down, don't think that you're off the hook and you're not going to have weeds all year. That's one of those other myths or misconceptions.

Let's talk a little bit about some of the different products. And one last thought, before I do that, is there's different strategies. Some people do what they call a single-app. So they'll time it, right. So maybe it's April 15th, two weeks before the ground temperature hits 55. Some people do a double-app, so it's a split-app. So they'll do two pre-emergents because the hardest part is timing. And it's hard to control timing because it's all about weather. And we don't have any say on the weather or temperatures or rain amount. So what a lot of guys do is they'll put down maybe earlier in the season, so a little bit after the snow melts, they'll put down one pre-emergent and then they'll wait and put another one down, right before the summer. Some guys do a split-app spring and fall.

It just all depends on your strategy. My feelings are, here's the thing I don't like about pre-emergents, is you're putting down a product over an entire lawn. So let's say you have a lawn of 1,000 square foot, and let's say on average, you get in the summer, three little patches of crabgrass. So you say, I don't want crabgrass. I'm going to put down a crabgrass pre-emergent on the entire lawn. So what you're doing essentially is you're covering your 1,000 square feet with a chemical just to prevent three patches, right? And that's a strategy thing. A lot of the times I like to say, you know what, I'd rather not take that risk of impact and I'll just deal with those three patches when they come up. I'll either pull them or use, but again, it depends on, every property is different.

If you're on a big commercial property and crabgrass seeds are blown throughout, and the lawn is 50% crabgrass everywhere, you need to really look at it and that's where you go, okay, I am working with a budget. I don't have the flexibility to just do what I have to do when I have to do it. So maybe I'm going to put a pre-emergent down. Maybe it's a split-app. One thing I like, some guys, if they have to put a pre-emergent, if they know the property over time, they know where the crabgrass is coming. They know the, we call them hotspots, the bad areas, because generally they're about the same. There's a couple of reasons for that. And so once you get to know a property, you know where they are. Maybe you could just do a liquid pre-emergent in just that area so you could spot-prevent.

But to do that you have to have history with the lawn. So different strategies on how you get to it. But here's some products we can talk about. The first one I want to mention is an organic product. It's corn gluten. There are kinds of products. There's one called Synergy that's used a lot in Colorado. It's a corn gluten with a fertilizer. It's all natural, 100%. These ones, they use sugar to bond the cornmeal to the fertilizer, which is kind of cool because the sugars can help feed the microbes in the soil. These ones tend to break down more by moisture and less by the biology in the soil. They've been around for about 30 ish years, these organic pre-emergents. One of the hardest things is they have to go down heavy. You're putting down 20 pounds per 1000 square feet.

I think they come in 20 or 40 pound bags. That's a bag for 1,000 square feet. If a homeowner's got 10,000 square feet, he's putting down 10 bags. 10 times 20 pounds, that's almost 1,000 pounds. So it's physically there, it's heavy, it's dense. If you've used lime, it resembles lime as far as the way that you apply it. It's just heavy. So you use 10 bags where some of these other ones, it might just be one bag because a bag will cover 20,000 square foot. There's ups and downs to all of them. But the nice thing is it is organic. It does work well, but the costs are very high on this and the labor is very hard. So there's that side. You also have Prodiamine and Dithiopyr.

Those are great traditional, non-organic pre-emergents. The Dithiopyr has a post and a pre-emergent in it so it can actually help crabgrass if it's already in the soil. So it can kind of kill both. But again, your costs go up. Prodiamine can work as well. It's all about timing and application. And so again you got to weigh all these things. What is it I'm trying to achieve? And then another one is, you have Preen, you'll see that The Home Depot that's for your flower beds, generally. You're going to put that down before certain plants bloom. It depends on what kind you get, will tell you, and then you won't harm any of the plants. And it'll just help to stop grasses from coming up in flower beds, which is nice because grasses can spread rapidly through those beds.

And then there's another one called Snapshot, that's what  a lot of contractors use. It's just the kind of thing that we would use in a nonorganic situation. So maybe a high end property that I can't have a budget or doesn't want to go with an organic, that's where Snapshot comes in. You're going to be closer to 150 bucks a bag for one bag. There is a generic that you can get about half the price for about 80 bucks, 75 bucks. And so there's all kinds of these pre-emergents, but I just want to get across, they can be a tool in your tool belt and there is value to them. Again, you have to weigh the impact versus not doing it. Again, if you don't get a lot of bad weeds or crabgrass, then why would you put a pre-emergent down? Because you can just treat it when it comes up and not have to create that environmental impact.

There is a cost associated with it if you go organic. I do like them in the flower beds because flower beds, those grasses spread in those open dirt and it's just, those are hard. So, that's one application I think is not too bad. But again, there are organic sources you could put down as well. But overall, it's just a tool that's going to help you minimize your labor. Minimize all the frustration or service calls. It's not perfect. Some people think you put them down, you'll never see weeds again. Not true. You just got to understand, first what's the area? Is it a lawn, is it a bed? What's the best product options to me? What are the prices, what's the environmental impact and what am I willing to tolerate and do? And then once you know that, you can pick your decision.

I will tell you that I have a lot of clients that we don't even use pre-emergents at all. We've built up this healthy soil food web, and we stay away from them as much as possible. But then we also do have some, some of my partner companies have some, and depending on where you are in the Salt Lake area, where crabgrass is such an issue that if they don't put it, they will lose the client, the customer will not be happy. So they're trying to use it in the least impactful way. Anyway, I hope that helps. That's a little bit about pre-emergents. Have a great day.

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