What sized pots are your plants in now? If the plant is young, I'd be wary of cutting the roots, which might slow growth down considerably for a few weeks if disturbed badly enough. If they're in small pots (6" starter pots, for instance), I'd wait until they're ready to be transplanted, then adding the perlite to that soil mix. Regardless, perlite does wonders for poorly draining or excessively soggy potting soils. If you're pots are retaining too much moisture, I'd agree with whoever recommended adding perlite. My soil is pretty light, but I still add at least a 30% mix for nearly all stages of growth.