Should You Use Weed Pre-Emergents in the Spring?

By Brian Mounts | Mar 06, 2020
Should You Use Weed Pre-Emergents in the Spring

As winter starts to fade away, it is time to consider if you should use a weed pre-emergent in the spring.   If you have a large front yard with turfgrass and it is important to keep a pristine yard to be the envy of the neighborhood or you don’t want a pesky letter from your homeowners association than a pre-emergent is right for you.

There are several benefits to using a weed pre-emergent in the spring to eliminate the growth of invasive weeds like crabgrass and very few downsides.

Two Important Benefits of a Pre Emergent in the Spring

#1 Benefit – Kills annoying weeds before they ever germinate.

This is the only solution for eliminating weeds before you would need to take more drastic measures later in the season.  Without using a pre-emergent in the spring you will be using bottle after bottle of weed killer on your yard later in a never ending battle to kill what you could have stopped from ever growing.

#2 Benefit – A pre-emergent can be used on a large number of turfgrasses targeting multiple species of weeds.

If your yard is a blend of grasses and not a pure Bermuda, Fescue, or Kentucky Bluegrass turf it can still be applied.  Most pre-emergent herbicides are designed to eliminate a large list of different types of weeds so whatever weed seeds blew into your yard from the neighbor down the street last summer and fall can be eliminated before popping up in the spring.

What weeds are eliminated by a pre-emergent in the spring?

The number of weeds that can be reduced or outright eliminated from your yard through the use of these kinds of herbicides is long and often very specific to the individual products.  While the most common enemy of turf grass aficionados is crabgrass, it is often geographic specific so look on the details of each product and make sure the weeds you want eliminated are in the list.

The following table includes a list of some of the most common weeds that homeowners and gardeners are concerned with showing up in their grass.

●        Barnyardgrass

●        Bluegrass, Annual

●        Carpetweed

●        Chickweed, Common

●        Chickweed, Mouseear (from seed)

●        Crabgrass(Large, Smooth)

●        Crowfootgrass

●        Cupgrassm Wolly

●        Foxtails, Annual

●        Goosegrass

●        Henbit

●        Itchgrass

●        Johnsongrass (from seed)

●        Junglerice

●        Knotweed

●        Kochia

●        Lambsquarter, Common

●        Lovegrass

●        Oxalis

●        Panicum (Texas, Fall, Browntop)

●        Pigweed

●        Purslane, Common

●        Pusley, Florida

●        Rescuegrass

●        Shepherd’s Purse

●        Signalgrass, Broadleaf

●        Speedwell, Persian

●        Sprangletop

●        Spurge, Prostrate

●        Witchgrass

●        Woodsorrel, Yellow (from seed)

What turfgrasses work well with the application of a spring pre-emergent?

It is important to identify the grass you have is acceptable to apply these types of products on it. Here is a quick list of turf grasses that most pre-emergent herbicides can be applied on.  Again always verify your grass type is in the approved list on the product that you choose to purchase.

●        Bermudagrass (established)

●        Bahiagrass

●        Centipede Grass

●        Kikuyu Grass

●        Seashore Paspalim

●        St. Augustine Grass

●        Tall Fescue

●        Zoysia Grass

●        Buffalo Grass

 

●        Kentucky Bluegrass

●        Perennial Ryegrass

●        Fine Fescue

●        Creeping Bentgrass

The best time to apply a pre-emergent in the spring

The key to a successful application of a spring pre-emergent is the timing of when it is applied.  Apply too early and it leaches out in the heavy winter rains before the weed seeds ever consider germinating.  Too late and the weed seeds have germinated and you just wasted your time and money.

The general guideline provided by companies that offer pre-emergent products is to apply it between  50 and 55 degrees. However, I recommend that when the weather window is correct anytime the soil temp is approaching that 50 degree mark is the right time to apply.

How does a water saturated lawn effect pre emergent application timing?

If the grass is heavily saturated the pre-emergent that you apply is not going to be able to soak into the soil to do its magic.  This is often a real challenge for homeowners that have a heavy clay ir red clay soil.  You want the soil to be dry when you apply so that it doesn’t wash away in the next rain.

The ideal scenario for applying

The best case scenario for the right window to apply your pre-emergent is for the soil to be a degree or two below 50 degrees and the weather dry and sunny for 3-4 days.  Allow the soil to dry out and the day before a rain event is predicted in your weather forecast apply the herbicide to your grass.  This will ensure that during that next rain that the chemicals are able to be absorbed into the soil to a depth of one inch.

Why does soil temperature determine a pre emergent application timing?

The goal is to apply before the soil temperature hits 52 degrees.  This will ensure that you have applied early enough to eliminate germinating Crabgrass which starts growing between 55 and 64 degrees.  Other weeds may have slightly different germinating temperatures so a little early is always best if you aren’t 100% sure of when to apply.

Remember a couple of warm bright sunny days in late winter / early spring can rapidly increase the soil temps.  Apply a little early if the soil condition is appropriate and you have the time.

Can you use spring pre-emergents at the same time during the calendar year every year?

When searching for when to apply a pre-emergent on your lawn most home owners are looking for an exact date that they can plug into their calendars and do every year, but that’s just not how nature works.  Relying on a calendar to time your herbicide applications will inevitably result in a late application that misses the germination window for your target weed species.

This is why the pros rely on soil temperature and soil condition to determine the application window.  There are several online tools that can give you a general ballpark for the current soil temperature in your area.  You can also use a soil thermometer to get an exact reading for your yard.

Picking between a granular or liquid pre emergent

Both will work, it really is up to your personal preference.  If you already have a spreader for applying seed and fertilizer to your lawn it can be utilized to spread a pre-emergent as well.  If you are considering a new spreader for this season take a look at my recommendations for picking the right spreader.

I ultimately will use both types of products for my clients that demand a pristine weed free yard for the full duration of the spring and summer.

If you elect to go for a double application this is the strategy that I encourage you to follow:

  • Aim to apply the first application of herbicide 2-4 weeks early.
  • This should be before the soil temps have hit 50 degrees, but very close.
  • The first application should be a granular pre-emergent like the Barricade DG formula.
  • This should be followed up several weeks later after the temps have started to creep up and are above the 50 degree mark.
  • The second application should be a liquid pre-emergent spray like the Prodiamine 65 WDG
  • When done correctly you can avoid any future applications of weed killer sprays during the late spring and through the summer.

Learn when you should fertilize your lawn in the spring.

Can you apply pre-emergent just once in the spring?

Yes, a single well timed application will often get the vast majority of your weeds under control.  I wouldn’t recommend applying the same product over and over during the early spring as a single application can work for 2 – 6 months.

I recommend the granular product if you will be doing a single application only versus the liquid spray.

The most popular pre-emergents available to homeowners.

  • Andersons Pro Turf Barricade Granular Pre-Emergent Weed Control
  • Quali-Pro Prodiamine 65 WDG
  • LawnStar Non-Ionic Surfactant

Get a jump on taking care of your beautiful yard by using a pre-emergent this spring and avoid the hassle, money, and time spent killing weeds the rest of the year.  Most tasks in the lawn and garden can be caught up with later in the season if you get busy and delay a project, but this is the one to make sure and time right and save lots of time down the road.