Should be 'weed and feed', not 'weed and seed'. 'lawn food': fertilizer 'feed': fertilizer 'weed': herbicide Herbicide: If its function is to kill weeds before they emerge from the soil , it is called pre-emergent. If its function is to kill weeds after they have emerged from soil, it is called post-emergent. Note most pre-emergent also prevents good grass to emerge from the soil, so you shouldn't use it when you are planting new grass or overseed. I wrote here why 'weed and feed' with post-emergent isn't a great idea: http://www.mitbbs.com/article_t/Living/32990265.html 'Weed and feed' isn't that great with pre-emergent either because pre- emergent has a specific time before which you should drop, and that time generally isn't good to feed the grass yet. To see what's the good time to drop crabgrass pre-emergent, check my update here: http://www.mitbbs.com/article_t/gardening/31631399.html