If a preemergence herbicide is justified on your lawn to control crabgrass now, most of those are available combined with fertilizer and you are forced to apply a fertilizer now. Look for a product with low nitrogen and be sure the majority of the nitrogen is a slow release N. Slow release sources include sulfur- or polymer-coated urea, urea formaldehyde, methylenediurea, dimethylenetriurea, or natural organic nitrogen. These are listed on the label as “slowly water soluble” or “water insoluble. Applying too much fertilizer now will encourage too much growth and could lead to problems later this summer such as poor root growth and disease. Additionally, since spring rains play havoc with mowing schedules, nitrogen fertilization can further complicate your mowing schedule by causing grass plants to grow too fast.