i know there are different guanos, one for flowering and one for veg. i have only used the flowering type. you can topdress with it, it works the best if you scratch up the surface with a fork or something then apply, and try to stir it in a little with the fork again. it keeps the fan from blowing the powder around and spreads it more evenly. the directions should be on the bag, mine was something like a tablespoon full for a 10 in" pot per month. i added a little extra because i didnt want to have to do it again.