Marijuana can grow under a variety of climate conditions, but in order to grow killer bud you’ll need to make sure your growing environment provides the plants with the right mix of temperature, humidity, air circulation, and exhaust.
Marijuana plants prefer temperatures similar to those that are comfortable for people. During the daytime, cannabis prefers 70-85 °F (21-29 °C) range when in vegetation. At night they prefer cooler temperatures. Flowering plants prefer temps slightly cooler than in flowering, in the 65-80 °F range.
Having your lights run during the day is an easy way to control this and ensure that temperatures are lower at night. You’ll need to make sure to exhaust heated air to reduce temperatures from lighting and to introduce new carbon dioxide which the plants need in constant supply.
Cannabis plants require carbon dioxide to produce energy, so you’ll need to ensure your grow area has a steady supply of fresh air. Small tents may get along ok with a single fan to exhaust, while larger setups in tents or rooms may also need an intake fan to ensure adequate air movement. You can combine your exhaust fan with air-cooled lights in a passive exhaust setup to use a single fan to keep lighting temperatures in check.
The volume of your grow area dictates the amount of air you’ll need to bring in. Using a fan controller can help you fine-tune the amount of air you exhaust while also allowing you to run larger fans at slower speeds to reduce noise and vibration.
Controlling humidity is important for healthy marijuana growth. Too much humidity can lead to problems such as mold or mildew. Too little humidity can dry out plans quickly since they can lose moisture through aspiration. Too low humidity also affects how much water the plants draw in, which in turn can cause a variance in how they process nutrients.
Proper air circulation needs to occur both above the plant canopy as well as below it. Oscillating fans let you cover a wider area. In grow tents, small clip fans can be used but for optimum air movement you may need several. Carbon dioxide needs to be replaced every 5 minutes, so a constant stream of circulated air combined with proper air exhausting/input will ensure the available CO2 is in supply.