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When to Apply Pre-Emergent for Crabgrass

When to apply Pre-emergent?

Soil Temperature Map

The best time to apply pre-emergent is before the soil temperatures reach 50 degrees for 10 consecutive days. Here is a link we use to find soil temperatures in your area. . The old wives tale states to have your pre emergent down before you see forsythias blooming. This is a good rule of thumb but it is not always accurate since we are paying attention to soil temperatures not air temperatures.

How do you apply pre-emergent?

Granular Pre emergent herbicide
Liquid Pre emergent herbicide

There are two common ways to apply pre-emergent.  There is a liquid form that you can use in tank sprayers, backpacks or any professional ride on machines.  The second more common way for a diy’er is to use a granular form. Granular form can be applied through a rotary spreader.  Either way of applying the product will accomplish the same results. One thing that is very important about applying the application is to make sure that it is spread evenly over the complete lawn.  It creates a “force field” effect. If any areas are missed it can allow crabgrass and weeds to break through causing a nightmare in the summer months.

How much pre-emergent should I be applying?

This question is answered by reading the label of the product you will be applying.  Every chemical and turf type is different. We here at PPLM like to split the application into two even treatments for better results.  We want to get half the rate down early to control the early stages of weed development. The second round of pre emergent will help aid in the control of late weed control and later crabgrass germination.  Over applying can cause stress to the lawn and under applying can cause a lack of efficiency. So always read the label before you start.

What should you do after the pre-emergent is applied?

After the application of pre-emergent is applied it should be watered in to activate the product.  This allows the herbicide to get into the soil and start the protection process.


Are there any problems when applying pre-emergent?

One of the main problems we know of about applying pre-emergent is spring seeding.  So many people want to seed in the spring. This is an ok procedure if you havent applied any pre emergent.  As mentioned above it does create a barrier that will not allow the seed to sprout. Also a lot of people want to aerate while they seed.  If you decide to core during spring seeding you will break down the barrier from the pre-emergent allowing crabgrass and weed seed to germinate and grow during the summer months which in return will choke out the already shallow and stressed lawn.