Like mentioned, what are you looking to do? Are you going to veg for a period of time or would you like to flower as soon as possible. Are you going to grow bushy or tall?

IMO the best way to utilize a 400 watt is to grow more small plants and lst (low stress training; tie down) them. You could fit 8 plants into that area if you only vegged them for around 2 weeks from good clones (or 4 weeks from seed). This gives you 50 watts/plant which is sufficient to produce over an ounce each plant. Obviously if you grow only 4, the plants have the potential to get even bigger. However the problem with growing big plants under 400 watts is the penetration factor, where the light is just not intense enough to make it far away from the lamp and through the foliage. Hence why I prefer lots of smaller plants that are tied down. A screen of green would be great.
Racerx Reviewed by Racerx on . how many plants for 400W's? How many plants can I grow at once with like 4 clf's adding to 400W? I hope for 2-5? Rating: 5