I just started using my Scott's superbloom again on all the pots. It can touch foliage and rhizomes since it's water saluable. I'll apply it once a week to already moist soil.
Otherwise as Leslie stated about a month before blooms, which is a tough guess these days. Just make sure to scratch it lightly into the soil, and water good. Depending on your pot drainage, 1tbsp and no more per pot. It does take time to break down, but you'll notice results really fast. Especially since they're waking up soon.
