Well, the obvious answer is: Before the weeds appear! But let’s take this step by step. Pre-emergent is a product that protects your lawn from weeds ‘before’ they sprout. There are a couple of times in the spring that you can effectively do this. 

The first time is before, and I repeat, before weeds start to show. So, if the winter freeze has passed and the weather is starting to warm up, you might want to make a quick call to your landscaping service. Hitting those weeds before they peek through, is crucial. 

Timing is everything. 

Once they start to grow, it’s too late to completely rid your lawn of these sprouting annoyances. 

If you are in doubt, call your landscaping company and get their opinion. They will know how your local weather is progressing and can give you a good timeframe for the pre-emergent application.

If you miss this opportunity, don’t stress too much. You will get another chance with the non-grassy (broadleafed) weeds. Late February is normally an effective time to have pre-emergent sprayed on your yard for these types of weeds. Although weather will need to be at or above 65 to 70 degrees to get the full effect. 

Winning the war on weeds can be complicated, but if you utilize the services of a good landscaping company, they can help guide you. After all, no one wants to spend their summer pulling weeds!