Do I need to reapply my preemergent if it rains heavily a few day after it is applied?

MML Staff_Erin H EXPERT April 02, 2008

First of all, I totally love you for using corn gluten meal, which I have been recommending for years. In fact, you'll see an article about it in the May 2008 Manage My Home newsletter.

Given the bright orange color of corn gluten meal, it's easy to tell if any is still sitting on the soil surface, so go out and check for that tell-tale film of yellow. If not, I suggest reapplying. The beauty of using corn gluten meal is that you don't have to worry about overapplying it (within reason -- if you spill a pile in one spot and leave it there, it will smother the grass. (And I'm not going to tell you how I know this.)

As background, corn gluten meal is most effective when it is lightly watered or rained upon (about 0.25 inches) within 5 days of application, and then allowed to dry out for a few days. Timing is critical -- you must apply it just before or right when the seeds of crabgrass and other early weeds start to germinate and form their starting root. (In spring, that's when the forsythia start blooming.) If you apply after they've formed a few roots, you end up feeding them with the nitrogen in the corn gluten meal.