The stress that cannabis plants experience when temperatures exceed 30 degrees is a factor more or less known by those growers who live in regions with warm climates, where summer temperatures can even surpass 40 degrees.
Growing cannabis during a heatwave, be it indoors or outdoors, is certainly a challenge. This is because high temperatures can severely affect the health, growth, and yield of cannabis plants.
While many cannabis growers are accustomed to implementing heat protection strategies in their grows (for instance, a shading mesh or an air conditioning unit), something many often overlook is the temperature of the irrigation water.
Keeping water temperature within the proper parameters is vital to guarantee a successful harvest. Here we explain its importance and some techniques.
Why is water temperature important in cannabis cultivation?
The temperature of the water used to water your grow can negatively impact the health of your plants as it can damage the roots, directly affecting their ability to absorb both nutrients and oxygen.
This is because water that’s too hot (above 23º) begins to lose its oxygen content, which is an important element for the roots and soil to be in optimal condition for the development of the plant.
Moreover, excessively hot water can create an environment within the substrate conducive to the emergence of harmful fungi like pythium or fusarium.
Just as cannabis plants need an environment within a certain temperature range (a minimum of 15 degrees at night and a maximum of 30 degrees during the day, with 23º – 25º being the ideal temperature), roots also need the water temperature not to exceed certain levels.
Often in the summer, in very hot regions like the south of Spain, it’s easy to forget that pipes get incredibly hot (even if buried), and tap water can come out at a temperature that can damage the roots of your cannabis plants. In the middle of August, the temperature of tap water can easily reach 30ºC.
Hot water damage when watering cannabis plants
- When the irrigation water is above 23ºC, plants can start having problems. At these temperatures, the amount of oxygen dissolved in the water starts decreasing, potentially causing root damage and affecting the plant’s entire metabolic system.
- Root damage: The root mass is highly sensitive to temperature. Therefore, watering your cannabis plants with excessively hot water can provoke a thermal shock that may affect the plant’s ability to absorb both water and nutrients. In severe cases, the plant can wilt and die.
- Alteration of metabolic processes: Cannabis plants need to carry out enzymatic processes to properly uphold their photosynthesis and respiration functions. Overly hot irrigation water can disrupt these enzyme processes, translating into a decrease in the plant’s growth and development.
- Loss of moisture: Watering your cannabis plants with excessively hot water can cause faster evaporation, resulting in less water reaching the roots. Furthermore, if the water is too hot, it can make the leaves lose moisture faster through transpiration, which could lead to plant dehydration.
- Destruction of beneficial microorganisms: Excessively hot water can kill the beneficial microorganisms that live within the soil, affecting the plants’ overall health.
Although this article focuses on the problems that excessively hot water can cause, it’s important to remember that when water is too cold, it can also wreak havoc.
- Effects of cold water when watering cannabis: Watering your plants with overly cold water (below 18 degrees) can stress your cannabis plants. This is a kind of shock that would reduce their metabolic capacity, consequentially slowing down their growth and affecting their yielding capacity.
Why are oxygen levels in the water important in cannabis cultivation?
As we’ve explained above, if you water your plants with water that’s too hot, the levels of oxygen dissolved in it will be lower.
The amount of dissolved oxygen in the irrigation water that you use for your cannabis grow is important because:
- It promotes nutrient absorption: If the water’s oxygen levels are correct, the roots will absorb nutrients more efficiently. This happens because, when the root mass has access to oxygen, it develops better, as it forms more root hairs that increase absorption.
- It prevents diseases and fungal infections: Adequate oxygen levels help prevent the proliferation of anaerobic microbes that can cause root rot.
- It stimulates root growth: The growth and development of the root mass equals that of the plant. When the roots have access to a greater amount of oxygen in the substrate, they grow longer, healthier, and with a higher density of root hairs. This directly results in an increase in yield, with more abundant and better quality harvests.
- It reduces heat stress: Well-oxygenated roots have greater capacity to absorb and transport water, helping the plant to stay hydrated in the face of high temperatures.
To reverse this problem, you can cool the water and then increase the amount of oxygen using water pumps, ozonators, or specific products for this purpose like Growth Technology Liquid Oxygen.
How to maintain the right temperature when you water your cannabis grow?
To avoid watering your cannabis plants with water that’s too hot, there are several measures that you can take. Depending on the type of cultivation you wish to undertake, you’ll need to choose one strategy over another.
How to Cool Water in Indoor Cannabis Grows
If you live in a very hot area where the summer temperatures rise considerably high, here are a few techniques you can implement:
- Use a Water Tank: Plan your watering schedule in advance so that, even if the tap water is too hot, it has time to cool in the tank (which should be placed inside the grow room). This is obviously assuming that you have an air conditioning system to regulate the room’s temperature to make it suitable for your cannabis crop.
- Cooling Bars: If you lack the time to cool the water in the tank with the aid of an air conditioning unit, you can speed up the process by placing cooling bars inside the water container. Remember to measure the temperature before watering with the help of a thermometer to ensure the water is in an optimal range (about 22-23ºC).
- Use the residual water from the air conditioning system: This is distilled water to which you can add the appropriate fertilizers and easily calibrate the pH.
- Use a Nebulizer and Humidifier: These devices help regulate the temperature of the grow room or grow tent. You can use them to speed up the process of cooling the water in the tank. Although this isn’t their main use, they may come in handy. These appliances are incredibly useful in controlling the ambient humidity, helping cannabis plants to have the appropriate levels as required in each phase of the cycle. Use this method only during the growth phase. If your plants are in the flowering period, you could cause excessive moisture in the flowers, which might induce the appearance of fungi and ruin your harvest.
How to Cool Water in Outdoor Cannabis Grows
In outdoor grows, conditions are more challenging to control. Therefore, you must pay special attention to your crop when you notice a heatwave approaching. Being prepared for climate fluctuations is the best strategy for a successful outdoor harvest.
If you observe that the temperature of the water you use to water your cannabis grow is too high, you can take the following steps:
- Let the water from the hose run for a while before using it so it’s not overly hot.
- Water your plants during the coolest hours, either early in the morning or at sunset.
- Use water from a well (if you have one) as it will be at a constant and cool temperature.
- Keep your water tank in the shade and use some cooling bars to lower its temperature. Make sure the water remains at about 22-23ºC.
How Can You Help Your Cannabis Plants Recover from Heat Stress?
During heatwaves, apart from controlling the temperature of the irrigation water, you can use anti-stress products that will help your plants withstand the heat and recover if you’ve mistakenly watered them with overly hot water:
- Biobizz Alga Mic: This is a biostimulant that promotes cannabis growth whilst improving the plant’s resistance to stress induced by pests, excess salts, over-fertilisation, or excessive heat.
- Advanced Nutrients B-52: This supplement provides the essential vitamins and minerals that marijuana plants need to withstand thermal stress. It is compatible with all growing and irrigation systems.
- Emerald Harvest Emerald Goddess: Its formula contains natural ingredients such as humic acids, vitamins, proteins, and amino acids. Not only do these help increase your plants’ yielding capacity in a natural way, but also strengthen them and help them recover from thermal stress. A highly effective all-in-one product for fans of organic cannabis cultivation.
- Aptus Regulator: It helps plants handle thermal stress and improves nutrient absorption, strengthening the plants’ natural defences. A perfect product that increases the thickness of the stems and helps your cannabis plants to quickly recover from stressful situations.
- Bio Tabs Boom Boom Spray: This is an anti-stress product in a spray format that enhances the plants’ resistance and helps them recover from thermal stress more quickly.
GH Terra Aquatica Urtimax: A nutrient-rich supplement that strengthens the plants and improves their resistance to heat, among other environmental factors that may pose a threat to them.
Conclusion
Controlling the temperature of the water during heatwaves is crucial to ensure a good harvest. Armed with the techniques explained in this article and some specific products, you’ll definitely be ready to face high temperatures and keep your grow healthy and fruitful.
