When to Water in Lawn Pre-emergent

Brendon Willis
watering pre emergent

If there is one thing that can make or break your investment in lawn care services – it’s proper watering. If a lawn is not properly watered after a treatment it can result in many months of your lawn not looking as good as it could.

Let’s break this down into a Q&A format to answer some of the important questions, and then see below for a quick video with a great example of what correct watering looks like.

Why is watering important for weed control?

Pre-emergent absolutely must be watered-in to do it’s job. Even during the times-of-year where it may seem odd to water your lawn – you’re doing it for the pre-emergent herbicide, not for the grass. You can read more in our blog on why we treat at odd times of the year. When our technicians spray your lawn, 99% of the sprayed solution lands on the surface (leaves) of the grass. Pre-emergent must bind to the soil particles, and it can’t do that unless it is rinsed off of the leaves and down into the soil.

How often should I water after pre-emergent?

Most of the pre-emergent manufactures tell us to water the equivalent of 1/4″ of rain per day for the first 4 days after treatment. Now – unless you have a well calibrated lawn sprinkler system, these instructions are kinda difficult to follow. However, one modest watering event for the first few days after a treatment will be acceptable.

How much should I water after pre-emergent?

If you have a lawn sprinkler system – for rotor head areas, 15-20 minutes per watering event is good, and 4-6 minutes per event for spray-type heads.

Spray vs rotor sprinkler system

If you’re using a hose and sprinkler, you’re probably going to be closer to 20 minutes per area.

The idea is to water enough to rinse the herbicides down into the soil, but not so much that you see run-off or standing water. If you water too much at once, it will cause the herbicide to run-off into the street, waterways, or to a concentrated area in your lawn. However, after several modest watering events, the pre-emergent will be adequately bonded to the soil and run-off will be much less of a concern.

How soon after a lawn treatment should I water my lawn?

We suggest waiting 12 hours. After 12 hours, any post-emergent herbicides would have had time to do their job. (Post-emergent herbicides need to be on the foliage to work.)

The Best Solution for Watering

Ideally, we treat every customer’s lawn the day before a perfect rain event. Unfortunately this never works out for everyone! We shot the video below of what you should be trying to replicate on your lawn for the first few days after a lawn spraying treatment. If you can re-create a rain shower like this for 15-20 minutes a few times, you’ll be in great shape! Proper watering will ensure your lawn care investment gives you the results you were hoping for.

More Reading

No more lawn care headaches, or your money back.

Schedule Conversation