Most people know know that they want to keep crabgrass under control and the best way to do that is to apply a pre-emergent herbicide. When it comes to the details though, there are some confusing misconceptions out there.
While you can find some sound advice, you can also find some confusing and conflicting information.
To set the record straight, one industry publication, Total Landscape Care took it upon themselves to do some of their own investigating and this is what they found.
They interviewed several field scientists who's only job is to conduct studies on turfgrass. It's no surprise American's love their grass, so turf is a billion dollar industry (especially thanks to all the golf fans out there!).
#1 No prior issues, no need for pre-emergent herbicides
I'm not sure that a lawn without weeds exists - even in a golf course setting, but some sources will claim that if weeds have been controlled for the past few years, the supply of weed seeds in the soil will be completely depleted. No weed seeds rationally leads to the misconception that there is no need for a pre-emergent as there are no seeds to emerge. From personal experience, I can tell you this is not true. Unless you live on an island, even the most diligent lawn care is no match for Mother Nature. It very may well be that indeed, you've eradicated every weed seed from your lawn, but that doesn't include what Mother Nature has brought in. It's possible that your neighbor or someone from a few miles away wasn't as diligent in their weed control and Mother Nature is only too happy to share their seeds with you. It's been a windy winter, and animals like deer and rabbits can also carry weed seeds great distances.
If that weren't bad enough: weed seeds are viable in the soil for a long time.
As the old adage goes: an ounce of prevention is worth a pound of cure. Also, keep in mind, regardless of whether you're doing it yourself or having a professional do your lawn care: pre-emergent helps prevent the germination of weed seeds. What that means is that no matter how good you or your lawn care company is, nothing is infallible against nature and it's more than likely you're have some breakthrough. That's normal so don't worry too much about it! Crabgrass that breaks through can be controlled by pulling it out, or by use of a post-emergent herbicide.
#2 Thick lawns don't need to be treated
It's true that thick lawns reduce crabgrass because there's less soil space for the weeds to geminate, but the key word is less. Crabgrass does have a difficult time competing against a thick, healthy lawn, but if the lawn has any stress during the spring or summer whether it's due to drought, or any other number of stresses, you can see crabgrass start to break through. Proper mowing, fertilizing, irrigation, aerating and detaching are the main keys to a lush, healthy lawn. Sometimes events beyond your control can cause a lawn to thin out. Just a few years ago we had such a bad drought that for the first time in recent history (the past 12 years) Madison issued a voluntary water restriction. While not everyone listened, many did.
Applying a pre-emergent herbicide can serve as an insurance policy that during times of stress crabgrass won't get the better of your lawn.
#3 Aerating breaks the pre-emergent control barrier.
Pre-emergent herbicides create a barrier in the soil that helps prevent weed seeds from germinating. It's a commonly held misconception that aerating will disrupt this layer, defeating the purpose of herbicide. Studies have shown in several published research articles that demonstrate no reduction of spring weed germination with spring aerating. Personally, we prefer a liquid aeration rather than mechanical. The liquid aeration we use adds beneficial microbes to your soil and helps alleviate compaction naturally (which is why you aerate). Core aerating can cause some concern with pre-emergents due to the amount of soil that's being disrupted. It's best to aerate first as soon as the ground is workable, and then go back and apply your pre-emergent. In the case of liquid aeration, the liquid product will help water in the herbicide so the two go hand in hand nicely together.
#4 Spot treating is more effective
You may think you're saving money or saving the environment by only treating what we call the "hot spots". Hot spots are those areas most prone to getting crabgrass, such as next to driveways and walkways. These spots are typically a little hotter and dryer than the rest of your yard because they're up against a hard surface and they dry out more quickly. Studies have shown that this application method is ineffective. A general broadcast application will help prevent breakthrough in the rest of your yard and will help eliminate post emergent treatment. Again, nothing is infallible. If you truly want a great lawn, you will likely need a post-emergent herbicide as well, but by doing the best you can with your pre-emergent, you reduce the amount of post-emergent you need.
#5 Post-emergent herbicides are better.
If you're looking for the least expensive, most effective, and most environmentally friendly (yes, I'm somewhat of a tree hugger, but I believe in a happy medium) way to control crabgrass, then beating most of it to the punch with a pre-emergent is your best bet. Post-emergents are somewhat unavoidable, but they should be kept to a minimum. There's is much higher risk of damage to your lawn if not applied properly, and most often times they require multiple applications. Early application of pre-emergent allows the desirable turf grass to mature and develop a nice thick canopy with less competition from crabgrass. Although post-emergent herbicides are formulated to target crabgrass, it's a complicated science. It needs to be applied during a certain temperature range, along with having a certain amount of dry time. This can be challenging during the hot humid months during which crabgrass tends to thrive. Not only that, but it is an herbicide. While it doesn't kill your desirable turf grass, it does stress it out a little.
.#6 Pre-emergent needs to be applied at as very specific time
Timing for pre-emergent is actually much easier than timing for post-emergent. Take it from someone who knows, post-emergent herbicides are tricky. Crabgrass starts to geminate when the soil temperatures (not air temperature) is over 50 degrees for several days. If you read any of my blogs, I'm always talking about what an opportunistic Mother Nature can be. In this case, the case of crabgrass, Mother Nature is helping us. It just so happens that forsythia also blooms when the soil temperatures reach 50 degrees for several days. That's when you should be putting down your pre-emergent. Keep in mind there are a lot of micro climates in Connecticut. The forsythia may not be blooming along the water in Branford at the same time it's blooming a bit earlier inland in West Hartford. As soon as you see the forsythia blooming in your neighborhood it's time for pre-emergent. It's better to put it down when you first notice the forsythia blooming rather than when they're almost done. There is more room in the front side of a pre-emergent application than in the back side because most pre-emergent herbicides are formulated for high efficacy throughout the season. Once those weed seeds have started to geminate, efficacy goes down. Again...the old adage of an ounce of prevention....
Over the years we've come to understand that a beautiful lawn involves a lot of effort, and timing is key. If you plan your lawn care out according to the weather instead of just the season, and use the calendar as a general guideline, you can have a beautiful lawn.
If all this is more than you want to tackle yourself, but you want a beautiful lawn, we've got your back. We are fully licensed in the state of Connecticut to apply fertilizer as well as weed and insect control, and we've got a lot of lawns and a lot of experience under our belt!
Let us be your lawn care partners.