Around the second week of April is when it’s time to apply crabgrass control. An easy way to remember this time of year is…TAX DAY. Once applied, it will need “watered in” within 3 days with at least a 1/4 inch of water and it takes up to two weeks to make its way to 1/4 inch below the surface. Crabgrass control should be applied for three years in a row and then you can take a couple of years off until they become a nuisance again and then start the three year process over again.
Options for Crabgrass Control: TurfBuilder with HALTS, ProScape with Dimension and ORGANIC Concern Corn Gluten.
These last about 90 days. You can apply a second application in about 6 weeks.
In late April you can sow grass seed the regular way. Grass seed needs ground temperatures off 55° in the mornings to germinate.
Question: Can I seed into an area where a preemergence herbicide was applied earlier in the spring?
Answer: NO. These herbicides are active in the soil for up to 120 days and their nature is to be absorbed into the root of a germinating weed (or turfgrass seedling), killing the very young plant. Most preemergence herbicides cannot distinguish between germinating crabgrass or turfgrass seedlings, so you’ll have to wait until July or August to consider seeding. Activated charcoal could be used to absorb the herbicide and allow for improved germination in emergency situations, but this product is very cumbersome to use. Alternately, you could remove an inch or more of soil (which should remove the herbicide), bring in new soil and the resod or reseed. Even with activated charcoal or removing soil, you would end up with somewhat compromising seedlings or sod having to survive a typical Pennsylvania summer, and that rarely ends well. Your best bet is to wait until August and seed then.