Compost is left over trash that turns into black gold... Meaning good soil. Some folks collect their grass and leaves throw it in a pile with food scraps (no meat or dairy) and keep it moist for three or more months and it turns into soil! WTF... Shit I don't know, some mother nature shit. Anyways, the biology in that compost is really high from breaking and eating down all that stuff shitting out soil ...now it's looking for more food to eat... Enter your top dress ..feed it the top dress, and it will shit out some really good nutrients for your plants. Mother Nature is a Bytch.