GrowCNanswered grow question 3 years ago Much depends on your medium (soil) and what nutrients are there to begin with. With most potting soils you are good for at least two weeks before even thinking about adding nutrients. I pay attention to the plant and let it tell me what to do. If the first true leaves are very dark green then the soil is hot and you should wait longer before adding nutes. If the 2nd or 3rd set of true leaves are pale green then I will consider staring very low dose fertilizer. Sprouts are fragile. It is better to do nothing or do it later than to burn them up with too much nitrogen.