Athosanswered grow question 5 years ago For soil, as long as you feed just enough, it is not actually needed to flush, but you do have to give it plain water 1 or 2 weeks before harvest. For coco, as long as you have regularly fed/watered to a healthy run off, it’s not needed, as long as your run off EC is kept in check, but do give it plain water 3 days up to a week before harvest.