Crabgrass pre-emergent herbicides are designed to prevent the seeds of many types of weedy grasses from germinating. The first application of fertilizer put down in the spring should contain this pre-emergent. There are several brand names of pre-emergent herbicides that are commonly used as an additive to your spring fertilizers. The Dimension brand is known to be among the most effective in the industry and it is what we use and recommend.
Here’s what you need to know about the timing of your pre-emergent application to make sure your getting the best results for your lawn. Although it is tempting to apply your first fertilizer application shortly after the snow melts in April, this is often too early and the pre-emergent will not last long enough to be effective late into May and June when it is needed most. If you applied a winterization fertilizer treatment the previous fall, that fertilizer has been stored in the roots and crown of your grass and will be used to jump start healthy growth in the spring, which another good reason why you can postpone your first spring treatment.
However, if you just can’t wait and you do apply your pre-emergent with fertilizer treatment in April, plan on using the same fertilizer blend again in June to prolong the pre-emergent herbicides effectiveness. This is a common practice amongst turf professionals, especially when we receive heavy rains in the spring or when a lawn is heavily irrigated.
You can apply the pre-emergent with fertilizer mix again in place of the recommended June/July treatment that will not contain the pre-emergent. Dimension is thought to last about 10-12 weeks effectively in the soil. However, if we get a lot of rain in April and May which we often times do, I would only count on about 6-8 weeks of effectiveness from your pre-emergent. With that being said, make sure to wait until soil temperatures are in the high 40’s to low 50’s to apply your pre-emergent application.
A good indicator that can help tell you when the time is right, is to wait until the lilacs bloom. Crabgrass will germinate when soil temperatures reach 55 Degrees Fahrenheit for a period of 48 hours consecutively, so make sure you have your pre-emergent freshly applied before your soil reaches 55 degrees. Dimension unlike many other pre-emergent herbicides has some post emergent qualities as well. It will kill small seedlings up to about 4 weeks old and up to the 2-3 tiller stage.
So even if you think you’re a little too late to apply. Making this application can still be very effective within the first couple weeks from the time you first start to see crabgrass emerging.