What are the best times to apply lawn fertilizer?
I had a soil test done by the University of Minnesota which indicated I needed a lawn fertilizer of 36-0-0 composition. I also have a big crabgrass problem. Armed with this information, I thought I would simply make four even applications from spring to fall and substitute the spring application with a crabgrass preventative fertilizer. I bought a bag of the crabgrass preventer of the the closest composition I could find. The problem came when I read an an article by the university which said that the best times to fertilize are late summer and mid-fall and not in the spring. What should my plan of attack be now?
Hennepin County Minnesota
The timing, amount, and number of nitrogen applications needed depend upon your lawn management goals. For simplicity, lawns are often referred to as "high maintenance," "medium maintenance," "low maintenance," and "very low maintenance." More nitrogen is needed to sustain a high maintenance lawn (3 to 4 applications) than a very low maintenance lawn (0 applications). Leaving the clippings rather than bagging counts as one nitrogen application.
Go to the following article (Table 2, in particular) from the University of Minnesota to get the details, including recommended number and timing of applications for the respective maintenance levels: Fertilizer Practices.
In any case, late summer and fall nitrogen applications are generally more beneficial than those done in the spring. If a spring application is desired (high maintenance lawn), it should go on when the grass is growing rapidly, usually late May or early June. This is too late to achieve crabgrass control with a pre-emergent. So, if crabgrass prevention is needed, apply the preventer separately (not in conjunction with fertilizer) at the appropriate time (late April/early May).