525mag· Country folks can survive
In southeast PA, fall is a better time to build turf - much better germination and root growth with warm days/cool nights than in Spring when it's cold, cold, and then blazing warm. I do a pre-emergent crabgrass and broadleaf app in mid-late April and don't have that problem - use Dimension or something similar that will have enough N with the herbicide to give you a boost into the summer. You want to get the crabgrass before it sprouts or when the leaves are very small. Use Trimec or Weed-B-Gone for the broadleaf. You want to do your spring fert in late fall/early winter of the prior year so that stuff is in the soil when the growth starts. A good fall app should last you to the time you do your pre-emergent app in late spring. Then follow-up in mid-summer with a lo-N grub app combo like Merit. Check with the golf, athletic turf, or pasture management guys in your area, or find out where lawn services are getting their fert and having soil tests done. In my area commercial turf supply houses do sell by the bag. I also know a guy that does Albrecht soil balancing and I get custom blends from him, as well as granular TurfPro, which is great organic fert and soil builder. Do a soil test and make sure your soil is balanced for the type of grass you want to grow before you go boosting the growth with nitrogen. Check out A. J. Turgeon's Turfgrass Management - great book if you geek out on grass.The reason for a spring feeding is to thicken up the turf before the weeds start sprouting. I'm sure you've noticed that weeds always fill up any bare spots in your yard, but more generally the best defense against weeds is a healthy turf.