Although it’s easy to overlook, the temperature and humidity of your growing area is an integral factor in determining the quality of your bud. Too much humidity will make your crop hugely susceptible to root rot, mold and bug infestations, while too little humidity can cause stress that will stunt the growth of your plants. And when it comes to heat, although your plants enjoy some warmth, temperatures too high will roast them and temperatures too low will stunt their growth.
There are dozens, if not hundreds, of strains of cannabis as well, and each strain tolerates variations in temperature and relative humidity (RH) differently. As a general rule of thumb, cannabis thrives in warm temperatures of 70 – 85 degrees Fahrenheit and with RH of anywhere from 40% – 60%. Some strains enjoy higher humidity levels, especially during the vegetative stage of growth, but when you start passing 65% – 70% RH, mold becomes a very real threat.
Garden supply stores and outlets like Home Depot and Lowe’s will generally carry a range of thermometers, hygrometers and dual-purpose devices starting for $8 – $10 and rising in price to upwards of $60 – $100. In a small grow space (a 2’ x 2’, 2’ x 4’ or 4’ x 4’ space, for instance) a single thermometer and hygrometer or dual device may be all you need. If you’re growing in a larger area, though, or you’re a stickler for total accuracy, it’s best to place 2 or more temperature / humidity measuring devices in your grow.
Good locations to take temperature and humidity readings include the center of your growing area, near the base of the plants’ stems, as well as along the perimeter. Many of the more expensive thermometer-hygrometers come with a metal-tipped probe that can be placed in the soil to test soil temperature and moisture levels.
If you live in a very dry climate, you may need to supply extra humidity with a humidifier. When using a humidifier, especially in your grow room, be sure to dismantle it completely for regular cleanings; humidifiers are already naturally at risk of becoming a breeding ground for mold and bacteria, so it’s especially important to keep your humidifier clean if it’s in your grow room.
Alternatively, if you live in a very humid environment (such as the Washington State or Florida) you may need to consider using a dehumidifier in your grow room. Humidity levels are especially important to consider during the budding stage of growth, since high humidity levels encourage mold to grow on your precious harvest. Most strains do best with RH of 15% – 30% during their flowering stage, so prepare in advance if you know humidity is a problem.