Generally you "flush" your plants if say you accidently drop a whole bunch of fertilizer in your pot but in this case you just want to remove any chemical residue from being in the plant when it's time to harvest. wait about a week to two weeks to flush your plants. just water them with some good water. You'll want to test it to make sure the ph is correct or you can go to Wal-Mart and pick up some spring water or something for like 50 cents a gallon (you might need 2) and just maintain your normal watering cycle. Something I've also heard of is adding some extract, ie: vanilla extract, strawberry etc. a few hours before harvesting and your plant will suck up the extract to give it a little flavor kick. Haven't tried it myself but I am interested in it.