Controlling your Cannabis growing environment at all times is the single most important factor to successful harvests. The best temperature and humidity for growing weed varies throughout the different stages of growth but in general, always maintaining air temperature between 70-80 degrees Fahrenheit (°F) and relative humidity between 40-60% is ideal throughout.
You’ll need a digital thermometer and hygrometer to measure temperature and humidity at all times, even when you’re not inside the growing area. Get one that also tells you the highs and lows every day as well. Make sure you can customize it to let you know via smartphone when things are out of your preset parameters.
Depending on your climate, you will potentially need a space heater, air conditioner, humidifier and de-humidifier to adjust to optimal conditions. Growers in wetter areas such as Northern California will need to reduce humidity while those in dryer conditions like Las Vegas or Denver will need to add moisture to the air. Likewise, frigid temperatures at nighttime when lights are off can reduce temps dramatically.
During the seedling or cloning process, temperature and humidity should be on the higher side – 75-80 degrees (°F) and 70-80% RH. Clones will stay more healthy and root quicker in a warm and humid environment. Use a clear plastic dome or lid to increase moisture in your cloning trays. Raise the temperature by utilizing a heat mat underneath the trays as well.
Once your clones have rooted, or your seedlings have developed several sets of leaves, bring down the temperature and humidity to between 68-78 degrees and 45-55% RH during the vegetative stage. Once you’ve initiated the Flowering Stage, bring temps slightly down to between 65-75 (°F) and reduce RH to 35-45% to avoid mold and bud rot. For drying and curing, lower your temps to 60-70 degrees (°F) and 45-55% RH to preserve terpenes and slow the drying process.
In conclusion, the best temperature and humidity for growing weed fluctuates depending on the growth stage so dial in your climate control for each stage and you’ll surely reap the benefits.