Your question is too vague to get a proper answer. A lot depends on what medium you are using to grow your plants. For example, I grow cuttings in rockwool cubes and then transfer to coco pots. I feed my plants the second they are born till a week before they die (I soak the cubes in quarter strength veg feed). If you were growing in ferted soil you might not feed until week 4 of veg, but this will depend on the soil you use.