The general rule for inside gardens is at least a square foot per plant. That means that each plant needs at least a 1 foot length by a 1 foot wide area of their own light. The bigger the plant, the more area it will need as it grows. If the plants are over crowded then they will not get light, if your plants are not getting light then you will have a poor yield. Plants that are over crowded are more likely to get moldy and rot.