Posted 21 May 2011 - 05:28 AM
It's not a problem. Flushing at the end of flowering accomplishes two things. First, it rinses away both nutrients and less desirable (often toxic) buildups from earlier fertilizations. The plant was absorbing all of this stuff before flushing. By rinsing it away, there will be less in the buds when you harvest, creating a smoother (& probably healthier) smoke.
The second reason to flush is because of flower production. Once flowers form, they need time to ripen before they'll make a good smoke. On many pot plants, new flowers will continue to form straight up until harvest. Any flowers that first form in the last week or two of flowering won't have time to ripen, and those particular bits of flower will yield a speedier, underdeveloped high. Flushing away all of the nutrients minimizes new growth so that more of the harvested bud is ripe.
Since flushing is a kind of overwatering, your plants will go longer than normal before needing water again afterward. So in your case, you might aim to flush a week before harvest.
Some people say use three times the container size in water to flush with. Some say flush until it runs out the bottom clear. Since the soil will be fully saturated after flushing, no matter how much you flush with, you can't really flush too much. Just run water through the pot until you think the soil is as clean as it'll get.