Not late. Most sources recommend applying once soil temps have hit around 50F. Crab grass and the spring weeds pre-emergents control start germinating once the soil warms to 55F so you want to make sure you apply before that time frame. If you apply too early or the soil not yet warm enough, the product will have ineffective results.

Pre-em's are typically good for a few months, so now, or last month are good for the early spring. You can repeat later in spring for more coverage into summer.

General rule of thumb is to apply when the forsythia are blooming. They bloom at the optimal soil temperature. I follow this and it's always worked.

" General rule of thumb is to apply when the forsythia are blooming. They bloom at the optimal soil temperature. I follow this and it's always worked. "

This is not at all true!! The soil temps have absolutely nothing to do with when forsythia may bloom. Forsythia has been blooming in my area for weeks already and the soil is still too cold to accept even very cold hardy plant starts....in the low 40's.

Blanket generalizations like this are rarely accurate and often unproductive. So are the "I've away done it this way and it works for me" statements that may or may not - usually not - have any relevance to anyone else.

Maybe soil temp isn't the determining factor, but the forsythia bloom should be plenty early to catch most of the weeds. We don't have forsythia in my area, so I go by whatever shrubs or trees awaken first. There used to be a tree nearby that always bloomed first, but they took it out, so I'm now looking for something else that awakens early. For us it is too late now to look. All the weeds are up as are most of the late blooming trees. We had roses on Feb 20, but others had roses at least a week before that. I don't get out enough.

@gardengal48 (PNW Z8/9)

Maybe you should contact preen and tell them to change their 'unproductive' website.

https://www.preen.com/learn/lawn-garden-tips/weed-control/get-rid-of-weeds/what-s-all-the-fuss-about-forsythia/#:~:text=Phenologically%2C%20the%20magic%20moment%20for,warms%20to%2055%C2%B0%20F.