Plants, like humans, need to breathe. The only difference is they breathe in carbon dioxide and breathe out oxygen, which is the opposite of us. Ventilation ensures not only that the air is fresh, but also that the temperature in the grow room is cool enough. If your grow room gets too hot and stuffy, it can stress out your plants and even cause them to stop growing. Consistent airflow helps the plant stay healthy.
Humidity control is also a crucial component of apartment growing. High humidity can cause dreaded mold and mildew on your plants, which can destroy your crop. Many growers put a dehumidifier or a humidifier in the grow room for this reason. Humidity levels should be between 50 percent and 70 percent for vegetative growth, and between 50 and 60 percent for flowering.
While high-intensity metal halide (MH) and high-pressure sodium (HPS) lights certainly have their place in indoor cultivation, LED lights are best for apartment growing. This is because LEDs don’t produce nearly as much heat as high-intensity lighting.
Happily, LEDs also use much less power than MH and HPS lights. This helps offset the somewhat higher initial cost of buying them. The fact that LEDs run more quietly is also a big plus for stealth apartment growing.
Jesus: Hey, Dad? God: Yes, Son? Jesus: Western civilization followed me home. Can I keep it? God: Certainly not! And put it down this minute--you don't know where it's been! Tom Robbins in Another Roadside Attraction