How to protect your plants from heatwave?

heatwave canna

Thermal stress and your plants

Heat stress can have a dramatic effect on your plants, but it's also easy to repair. What should you do when the thermometer rises to 28ºC in your grow room or greenhouse and continues to rise? Here are some methods to beat the heat and be able to harvest dense and tasty buds.

Your plant can only withstand a certain amount of heat and light. If your cannabis begins to show signs of stress on the leaves near sources of light and / or heat. Your leaves will have brownish yellow or brown spots and can usually appear scorched in places when there is too much light. It is also common for the leaves to curl up or down, bend inward, like cones, and the jagged edges of the leaves to begin to lift. Even plants grown outdoors in the open can suffer from the intense heat of summer. Besides the need for large amounts of water, here are the symptoms you might experience if you were growing in a red zone.

  • Damage from some insects can quickly destroy your plants in hot, dry weather - they reproduce up to twice as fast during these times.
  • Excess heat conditions cause burns and leaf diseases, whether wet or dry, they invite burns, molds, fungi and bacteria that cause disease in your crop.
  • Anaerobic bacteria and decay fungi in the lower parts of cannabis plants often prefer warm, humid conditions around the roots because at warmer temperatures the water retains less oxygen, which weakens the roots. .
  • Poor quality, low yielding buds are a telltale sign of growing stress in excessively hot growing conditions.

Solution: Find a way to monitor the temperature. Control the heat by any means necessary by following the steps described below.

5 tips for controlling heat in the growing room 

Inside, find a way to lower the temperature by increasing the air circulation in the grow area. Having a small fan blowing on top of your plants will help prevent hot spots from forming directly under your grow lights.

You can consider positioning crop lamps higher from the top of plants if heat is a problem.

When growing, it's best to try and keep a comfortable room temperature at all times for optimal growth. If it's too hot for you, it's probably too hot for your plants.

Keep the roots cool : If you can keep your roots cool, it will help your plant cope with the heat affecting the top of the plant.

When cannabis plants recover from heat shock, some growers recommend the use ofkelp seaweed extract (often available as a liquid fertilizer) to help plants recover from stress and possibly protect plants from heat stress in the future.

Many indoor installations will require you to ventilate the hot air using a fan or exhaust system. By creating good suction with an efficient exhaust system and adding a carbon scrubber, you can also eliminate all of the odor of the culture room.

An oscillating fan will circulate the air around the room and provide a light breeze for your plants.

Outside , you have fewer options to reduce the heat during a heat wave, but you can monitor your local weather through a weather forecast.

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It is possible to partially protect your plants when you know the temperature will heat up. You can also adjust your watering schedule to make sure the plants have at least plenty of water.

Some tricks to try when you know that the weather outside will be hot or dry:

  • water the plants in the evening or early in the morning  to help prevent water evaporation during the hottest hours
  • Keep the roots cool , for example by placing your potted plant in a ceramic pot to insulate the roots from the sun. Some growers dig a hole in the ground to place their potted plant in, as the soil is usually cooler than air when the temperature is high.
  • THEkelp extract for roots can help protect against heat stress
  • increase shade  to reduce the heat felt by the plants, you can use an old leaf or other cloth as a short term solution, or get a professionally made 'shade sail' specially designed for outdoor shade . It's important to remember that shade the plants for more than a few days will make them softer than in the sun and you may need to slowly re-introduce full sun to avoid them being shocked by the intensity. light.
  • move potted plants : fortunately with potted plants, it's usually easier to move them out of direct sunlight during a heat wave

When growing cannabis outdoors, it often takes a few weeks for the plant to regenerate after a hot or dry period. Prevention is therefore the best medicine for outdoor plants.

Hightimes also offers some techniques as a bonus :


If you already own an industrial air conditioner, chances are good that you will rest easy (even if you are not yet safe from all the problems). However, for most growers there are certain things you will want or need to do to ensure healthy plants and high quality harvests. Naturally, the first step is to try to lower the temperature by applying this method of air conditioning. This makes it a serious investment for those who can afford it.

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Note: ventilation systems generally exchange indoor air with outdoor air to provide cooling. This means that you are probably going to let some smells pass outside. In-line carbon filters or odor neutralizers can be added to this process to absorb as much odor as possible.

Water-cooled heat exchangers

If you have access to a free stream of water that stays cold and plentiful, a water-cooled heat exchanger can be a great way to keep a greenhouse cool during the hottest months of summer or even the summer. year in a closed place.

The water that circulates in a heat exchanger remains clean and very useful afterwards. Liquid cooling can be very efficient and the heat can be directed as far away from the grow room as possible, depending on the conditions of your circulation lines. Water chillers, reservoirs and geothermal principles can also be used to cool water in a heat exchange system.

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Tip: Just because your water is cold and plentiful in winter and spring, doesn't mean it will be the same in summer. A water-cooled heat exchanger is highly dependent on the temperature of the water used to function properly. Make sure that the air sucked in is cooled enough to handle the necessary temperatures of your precious crop.

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Fan cooling

Extractor fans for grow rooms, tents, and indoor greenhouses can be effective at cooling even during the summer months but that largely depends on where you live and how lucky you are with it. weather. Even the best fan-cooled installations (i.e. incoming / outgoing exhaust) generally require a difference of about 10 ° C between the outside air temperature and the desired ambient temperature to operate within optimal limits of. Culture.

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Cooling of hydroponic crops

Hydroponic methods of water culture, such as the nutrient film technique (NFT), deep-water culture (DWC), recirculated deep-water culture (RDWC) and aeroponics, require little or no culture medium. Bare cannabis roots drink freely in a circular, well-ventilated, mineral-rich solution. Temperatures in the hydroponic tank above 25 ° C can create problems such as poor absorption of nutrients or even root disease in some cases.

The good thing about hydroponics in hot weather is that savvy growers cool the nutrient solution instead of the air. It is much more efficient in terms of equipment costs and energy consumption. Remember that these are the plants to keep cool, not the air ...

What about less expensive solutions?

If you have a budget and you can not spend a lot on greenhouse technology, here are some suggestions:

While not exactly inexpensive, air-cooled HID light reflectors are a great way to dissipate heat from grow lights before they even enter the growing environment.

Alternative light sources such as LEDs (Light Emitting Diodes) or LECs (Glowing Ceramics, such as Ceramic Metal Halides) can cost more for the same size area as HID lights, but they often produce much less heat. for the level of bud production they offer. Another added benefit to offset the upfront cost is the fact that you use less electricity to power them or any other equipment you could use to cool your grow room, which means your cooling needs and power consumption decrease. proportionately.

A simple and economical way to reduce the heat in the grow room by 30% is to operate your HID light fixtures through remote ballasts. These are lighting systems that allow the “driver” (which turns on the lamp) to be placed in an area outside the culture room, at the other end of the cord, thus maintaining the heat generated by the electronic components away from your plants.

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(Photo by Erik Biksa)

Fans cool lights, maintain room temperature, and allow cool air to circulate through the canopy. 

Plant Genetics

Some cannabis strains handle heat better than others, some even crave it. The sativa Exotics (e.g. Cambodian varieties) may actually prefer higher heat coupled with high humidity levels compared to more common household hybrids. Desert stumps, like Afghans, can also handle heat, but are not resistant to humidity.

Strains with sensitive roots or prone to insect infestations are also not recommended when growing under less controlled conditions during the warmer months. Because frequent watering is necessary in hot climates, the chances of root rot are significantly better in warm, moist soils.

The summer season is approaching, take advantage of these tips for prevention, a good holiday.

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Tags : Agriculture / GrowselfpermaculturePlantingPrevention
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The author weed master

Weed media broadcaster and communications manager specializing in legal cannabis. Do you know what they say? knowledge is power. Understand the science behind cannabis medicine, while staying up to date with the latest health related research, treatments and products. Stay up to date with the latest news and ideas on legalization, laws, political movements. Discover tips, tricks and how-to guides from the most seasoned growers on the planet as well as the latest research and findings from the scientific community on the medical qualities of cannabis.

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