What should you do when the thermometer climbs to 85°F in your growroom or greenhouse and continues to rise? Put down that cool drink and start thinking about how you can beat the heat so you can still harvest dense and tasty buds.
What Can you Do When It Gets Realy Hot
If you have an industrial air conditioner already keeping things cool, chances are you’re resting easy (although you’re still not immune from every issue to be aware of). However, for most growers, there are some things you’re going to want—or need—to do in order to ensure healthy plants and high-quality harvests. Naturally, the first step is to try and lower temperatures through the following methods.
For every 1,000 watts of high-intensity discharge (HID) lighting in your growroom, you’ll want around 3,500 to 5,000 BTUs of cooling power. The range is wide because not all air conditioners perform up to their claims, coupled with the fact that different types of lamps and ballasts produce different levels of heat.
Be aware that a good-quality AC unit—i.e., a “split” style—doesn’t come cheap. In fact, it can be the most expensive piece of growing equipment you’ll own, making it a serious investment for those who can afford to purchase one.
Water-Cooled Heat Exchangers
These are essentially growroom radiators, although they’re quite a bit different in construction from an actual car radiator. The hydronic fins in a good-quality heat exchanger are very fine, giving them a large surface area in a small-dimensioned cube to scrub away heat from the fluid that’s circulated through them, originating from the growroom.
If you have access to a free stream of water that stays cool and plentiful, a water-cooled heat exchanger can be a great solution for keeping a growroom or even a greenhouse cool during the hot summer months—or even year-round in a sealed growing environment.
The water that circulates through a heat exchanger remains clean and very usable afterwards. It’s just much warmer than when it started out—and plenty of water gets circulated during the course of a hot day. Liquid cooling can be very efficient, and the heat can be directed as far away from the growroom as your circulation lines allow. Water chillers, tanks and geothermal principles can also be used to cool the water in a heat-exchanger system.
Fan Cooling Your Growth
Exhaust fans for indoor growrooms, tents and greenhouses can be effective for cooling even in summer months—but this largely depends on where you live and whether you’re having luck with the weather. Even the best fan-cooled set-ups (i.e., in/out exhaust) usually need about a 15°F difference between the outdoor air temps and the desired indoor temperature to work near the optimal range for growing cannabis.
Pro-tip: For every 700 cfm (cubic feet per minute) of exhaust output that your shutter-style fans push, you need 1 square foot of opening to ensure that static pressure doesn’t create excessive resistance to air movement. Typically, this is accomplished with a motorized or thermal shutter opening, available in various sizes.
Hydroponic Crop Cooling Your Grow
Water-culture hydroponic methods like nutrient-film technique (NFT), deep-water culture (DWC), recirculating deep-water culture (RDWC), and aeroponics require little to no growing medium. Bare cannabis roots drink freely from a recirculated mineral-rich solution that is kept well aerated. Temperatures in the hydroponic reservoir over 75°F can create problems like poor nutrient uptake or even root disease in some instances.
The cool thing about hydroponics in warm weather is that savvy growers chill the nutrient solution instead of the air. This is much more efficient from an equipment-cost and power-usage perspective. Remember, it’s the plants that need to be kept cool, not so much the air. Think of sitting with your feet in a cool stream on a very hot day … thermodynamics is fun!
What About Some Less-Expensive Solutions?
If you’re on a budget and can’t spend a lot on growroom tech, here are some other suggestions:
Indoor or Greenhouse Lighting
While they’re not exactly cheap, air-cooled HID light reflectors are a great way to remove heat from grow lamps before it ever enters the growing environment—and since most growers end up buying a lamp reflector anyway, it’s often not much more of an investment as a startup cost. Good-quality air-cooled lamp reflectors spread light evenly and can be sealed off from the environment, which means you won’t suck out carbon dioxide or telltale odors along with the heat you discharge from the growroom to send outside.
Alternative crop-lighting sources like LED (light-emitting diodes) or LEC (light-emitting ceramic, such as a ceramic metal halide) can cost more to buy for the same-size area versus HID lights, but they often produce considerably less heat for the level of bud production they offer. Of further bonus to offset the initial cost is the fact that you use less electricity to power them or any other equipment you may use to cool your growroom—meaning that your cooling needs and power draw decrease proportionately.
Some cannabis strains deal with the heat better than others—there are even strains that crave it. Exotic sativas (for example, Cambodian varieties) may actually prefer higher heat coupled with high humidity levels versus the more common domestic hybrids. Desert strains like Afghanis may also take the heat, but they won’t do well with high humidity.
Strains with sensitive roots or that are prone to insect infestations are also not advisable when growing in less-controlled conditions during the hotter months. Because frequent watering is necessary in hot climates, there’s a much better chance of getting root rot in hot, wet soil conditions.
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