I guess it all depends on where you are. In southern CT, I have been successful with late April applications. It happens to usually coincide with the Forsythia blooming. If it's a week or two early it shouldn't matter. Most pre-M's last a long time (3-4 months).

From trial and error over several years, I have pinpointed to put mine down around Feb 1st here in Central Oklahoma. I also see alot of dormant Bermuda lawns "painted" green with a preemergent this time of year.

The temps fluctuate alot this time of year, and on the South side of my house I can see a few shoots of Bermuda about a half inch long emerging.

My advice, if you grow Bermuda turf, put preemergent down when it's still dormant in late winter.

I'm in NC, and some of those indicators you mentioned are good (when Forsythia blooms), but if you have an unusually warm winter (which we have had for 2-3 years) you're screwed if you wait until the right indicator is triggered, because all the grass weeds are growing then too.

I put out my prevent-everything-from-germinating pre-m and a fertilizer app also right now (mid Feb), then again around mid to late Apr/May 1. That usually will keep most everything including all the grass weeds from germinating, unless they already germinated over fall to winter. That usually stops everything you don't want growing dead in it's tracks.

We don't have forsythia so I use the blooms on the tree at the church a couple streets over. So for San Antonians, that tree bloomed last week.

Wow, firstandgoal, I didn't think we had to put it on so early here. I was planning on applying some this weekend (so of course, there's a chance of snow). I hope I haven't waited too late. Last year, I waited until the first weekend of March, which was definitely too late.

My understanding is that crabgrass will start to germinate when ground temps are consistently in the 50's, so I use this map and zoom in on my area, when the ground temps get to 50 degrees for a few days, I put my down.

http://www.greencastonline.com/SoilTempMaps.aspx

When the cows come home?

When hell freezes over?

When pigs fly?

Those would be my favorite crabgrass timeline descriptions.

hi,
i'm in northern california (San Jose; 95118). when would I need to use pre-emergent?

thanks,

lutzd79, great link, thanks for posting it. I'll give this a try, it makes a LOT of sense.

One thing I did notice when I changed the region to "Great Lakes" it put the timeframe back to Sept 07. I'm hoping they update the region maps, as the zooming in helps.

zhotster,

I went on the website to check out the "great lakes" issue you mentioned. All I do is use the national-today map and just point my mouse on my area and click, each time I click it zooms in closer. It remains on todays data. Try that out and see it meets your needs a little better. Thanks.

Thanks for a good link.

You might also check around for a local soil temp link. One of our tv weather stations runs one at the two inch and six inch depth updated daily on their web site.

lutzd79, that did the trick! It opened a new window with exactly the same national map, but clicking on that map gave me my local temperatures.

Thanks much!

As far as rcnaylor's suggestion, I did some searching but couldn't find anything local for me. I did find a lot of folks refernce/refer the site that lutzd79 uses.

That link is the coolest thing I've seen in a long time. Thanks. I'm making it a hot link for those who didn't want to copy and paste.

With reference to the thread at hand, if you are in or below the bright green band on the map, you need to be thinking about crabgrass sprouting.

Here is a link that might be useful: National Map of Soil Temperature

So I'm right outside of Philadelphia PA and currently showing in the blue-green aqua color. I was thinking about applying this weekend (not just for crabgrass but broadleaf weed as well). Do you think I should wait longer or pull the trigger?

Our forsythia has large buds but has not yet popped (I'd give it 2 weeks max, probably closer to a week).