Hello. My name is John Henning, and I have been working for Dundee Nursery for over 25 years. In all that time I have not seen a spring thaw like this year.
With an early warm up like we are having this year, one of the most frequently asked question is “When should we apply our crabgrass controls?” It is a common question every spring but is asked even more often this year. The answer will vary a little from year to year. When we have an average spring we tell people to apply it during the first two weeks of May. However, this is not the average and I think now is a good time to start putting it down. Keep in mind that most controls are effective for around 8 weeks in the soil, and if we have a long cool spring, crabgrass seeds may still germinate into June. To insure the best results it may require a second application in around 6 to 8 weeks.
Soil temperatures, not the air temperatures, play the biggest role in determining when the crabgrass seeds start to germinate. Even though it may be hot during the day, the evening temps may keep the soil from rising too fast. The cool nights are what may lengthen our spring season. This is why I would recommend the second application of your controls.
There are two ways you can get two applications on your lawn. You can apply a crabgrass control with fertilizer now and the follow up application may just be crabgrass preventer alone -OR- you can apply the crabgrass preventer in late May when you apply a weed-and-feed for broadleaf weeds like dandelions and thistle.
If you feel that you missed the prime time for best control there are other pre-emergent controls that can be put down up to 4 weeks later and still give you great results. Look for a product containing “Dimension” (dithlopyr) as this will also prevent some broadleaf weed seeds from germinating.
One last way to determine the prime time to apply your preventers is to look around your yard and neighborhood to see if the lilacs are starting to bloom. The lilacs tend to bloom at the time soil temps are prime for seed germination. Areas that warm up quicker, like along streets, may need the application a week or so sooner. I hope you can use this information to prevent crabgrass from becoming a problem in your yard.