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Plant Water Temperature for Cannabis

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Plant water temperature is incredibly important when it comes to watering cannabis plants. It also tends to be an issue that many new growers have, although it can be something that affects even experienced growers. If you completely ignore the temperature of your water you could end up with issues that you don’t even recognize, and end up miss-diagnosing them, especially if you don’t even consider temperature when watering. In this post we’re going to talk about how to check water temperature, as well as what the perfect temp is and how to solve temperature related issues with your cannabis plants.

How to Check Plant Water Temperature

When watering, many growers tend to simply grab the hose and start. However, it’s incredibly important to measure the temperature of your water, especially if it seems to be particularly cold or warm. If the water is too hot or cold, you’re putting your plant at risk, as this can cause many different problems. In order to avoid this, all you need is a thermometer.

There are an incredibly large amount of water thermometers, and most of them are incredibly affordable. Some EC and pH meters can also measure water temperature accurately. Now that you know how important temperature is, and how easy it is to keep under control, you’re bound to start checking before every watering. Depending on the temperature, water can actually suffer certain changes in its composition, including oxygen rate.

Extreme Water Temperature Problems

pH and EC levels are some of the most important factors when it comes to watering plant; these factors are incredibly important when it comes to how your plants’ roots develop, the amount of nutrients they can absorb and the general health and state of your plants. Almost every growers knows that these two factors are incredibly important, however most of those growers often forget the third most important factor, which is water temperature. If there are wide variations in temperature, you may have some unwanted issues; water that’s too hot or cold will end up not being able to absorb certain nutrients.

Cold Water

Cold water tends to be more of an issue than hot water. This is usually because water is much colder during the winter months, especially for growers that use their own tap water. Anything lower than 15°C will cause your plants’ roots to almost entirely cease growing and can hardly absorb some nutrients such as phosphorus. This element can’t be absorbed at temperatures lower than 10-15°C, causing clear nutrient deficiencies.

The most obvious symptom of cold water is that your plants’ leaves will begin to go a dark color, similar to purple, with clear deterioration in the stem and leaves, which will also become super brittle and break easily, drastically reducing the final yield obtained.

Warm water

This problem isn’t as common as cold water, although it may happen in certain climates or at certain times of year. This factor causes your plants to stop absorbing nutrients from your water due to the lack of oxygen (the warmer the water, the less oxygen contained in it). From 20°C onwards, oxygen is reduced to around 9ppm (parts per million), with 23°C being the maximum temperature for nutrient absorption, with about 8.5ppm oxygen.

The direct consequences of warm water are the clear delay in plant growth, as well as rot appearing near the roots and substrate. This problem can signify the end of your entire grow if you don’t discover it fast enough.

The Importance of Oxygen when Watering Plants

Water is hydrogen and oxygen, although the amount of oxygen in a body of water depends on water temperature, atmospheric pressure and amount of bacteria. Oxygen helps your plants to easily absorb nutrients, allowing them to grow much stronger. This is why it’s hard to get the perfect amount of oxygen in your water without keeping temperature in mind.

Many growers get air pumps for their water tanks or nutrient tanks in order to help their plants to grow strong and healthy, however in order to do this properly you need to keep close control over the temperature in the tank.

Plant Water Temperature in Cannabis grows

Each and every plant is its own being and there’s no universal code for how you should treat every single plant. There are many different strains, each of which can be grown in different areas and climates. All of them, however, still need a stable temperature in their water – not too cold, not too hot.

If you want your plants to grow out healthy roots that can absorb nutrients, we highly recommend keeping the temperature between 20 and 25°C. The perfect temperature is 23°C, allowing for the perfect amount of oxygen. Your plants should be able to absorb the maximum amount of nutrients possible at this temperature, allowing for strong and healthy growth.

Growing in soil

When grown in soil the perfect temperature is between 20 and 23°C, keeping in mind that the soil acts as a sort of wall between the inside and outside, which allows for slight variations in the temperature in your grow room and water. The real issues start to arise when growing hydroponically.

Growing in hydroponics

When growing hydropnically, there is nothing between your plants’ roots and the water that comes into contact with them – the water is their substrate. In this situation, your plants’ roots are in constant contact with water, which is where temperature really comes into play. When growing in hydroponics, colder water (18°C) can help the roots to grow out to begin with, although not many nutrients are absorbed at this low temperature. Small plants, however, don’t need very many nutrients anyway. Once they’ve rooted and they begin to feed more, you’ll need to increase the temperature to 23°C, absorbing as many nutrients as possible while also keeping a decent oxygen ratio.

Ideal Plant Water Temperature for Cannabis Plants

Water temperature might just be one of the most important factors when it comes to healthy cannabis plants. If you follow the advice given in this post you shouldn’t have any issues keeping it balanced. Plus, there are also devices that can actually help you to adjust cold/hot water temperatures.

If you want to cool your water down, you’ll need to keep a few things in mind. Grow lights can generate high temperatures, which can cause the water to heat up. There are plenty of ways to do it manually, although this can be hard to keep up during the entire growing process. The best thing you can do in this case is to use a water cooler which can keep the temperature constant over a 24h period.

However, if you want to heat up the water, you’ll need to use a heater in your water tank. These devices can increase the temperature of your water by a few degrees, allowing your plants to absorb more nutrients from the water.

Now that you know how important water temperature is when it comes to growing cannabis plants (and plants in general) you’re aware of the issues that cold or hot water can cause in your grow. Hopefully, now you know how to easily measure your water or nutrient solution, as well as correctly oxygenate it. When done right, you can obtain some truly professional results from your plants. Let us know if you have any questions or suggestions in the comments below. Until next time!

Plant water temperature in cannabis is extremely important for the health of your plants, especially if growing using a hydroponic system.

Control Root Zone & Fertigation Water Temperatures for Better Marijuana Growing Outcomes

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Air and fertigation water temperatures impact the growth rate, health, and harvest weight of your marijuana plants. In indoor grow ops, you can totally control these temperatures. In outdoor growing, you have a harder time controlling these factors, although I’ve worked with outdoor growers who chill their nutrients water and (in greenhouses) use climate control to control air temperature.

My focus today is on the many impacts of fertigation water and root zone temperatures on the health and productivity of your marijuana plants. Cannabis roots evolved in nature, where below-ground temperatures are cooler than the aboveground ambient temperatures. Water entering a natural outdoor root zone comes from rain, which is often cooler than prevailing air temperatures.

When you’re growing cannabis and providing the water your plants’ roots intake, your plants benefit most when you deliver water that’s 67-68°F. This temperature has been shown to protect roots from heat stress, aid in maximal uptake of nutrients elements, and is the temperature at which water oxygenation is very high.

Water and root zone oxygenation is an important growth and vitality factor for your marijuana plants. One reason you see incredibly fast and robust root growth (especially during cloning) in pure hydroponics systems such as deep water culture and aeroponics is that the root zones are filled with an extraordinarily high amount of oxygen compared to root zones using soil and other solid media. Growers are wise to use pumps, bubblers and air stones to oxygenate water in pure hydroponics, and in drip irrigation and other hydroponics systems.

The use of professional root zone materials such as Grodan rockwool and the highest grades of coco coir and soilless mix often increases oxygenation in solid-media root zones. Growers using generic soil and peat-based mixes should add extra-coarse perlite so that it is at least 10% if not more of total volume. This increases porosity, drainage, and oxygenation of soil and peat mixes, which otherwise tend to pack down and become overly dense and waterlogged, reducing oxygenation, impeding root growth, and decreasing plant health and productivity.

Fertigation water temperatures above 68°F can decrease root zone oxygenation and create other problems. The warmer the irrigation water is, the less dissolved oxygen it can hold. Water that’s too warm and stagnant can even become anaerobic, which is deadly for your marijuana roots.

Another problem is that warmer irrigation water is an ideal environment for harmful microbes that rot roots and rob the root zone of oxygen. Some growers run their indoor grow rooms above recommended temperature range when carbon dioxide is added to indoor grow room air during lights-on cycle because in C02 grow ops, you can allow marijuana grow room ambient temperature to creep higher than the usually recommended 74-78°F– added C02 helps cannabis plants use higher ambient air temperatures for accelerate metabolism that produces faster growth and bigger buds.

Regardless of what the optimum air temperature is for your grow op, the temperature of the root zone and fertigation water still matters. I urge all growers to use a chiller in the root zone. If the grow room is hot, and the fertigation water is inside the grow room in a hydroponics reservoir without a chiller, the water is most likely way too hot too.

Quality water chillers cost several hundred dollars, and require some hardware and properly-tight seals to prevent leaks, but they pay for themselves many times over. In hot grow rooms with or without C02, chilled fertigation water frequently recirculated in the root zone greatly reduces plant stress. Plants grow faster and are more productive because chilled water holds more oxygen, is far less likely to contain pathogens, and relieves root heat stress. Some growers have discovered that using chilled fertigation water allows them to reduce air conditioning costs, especially in grow rooms run hot because added carbon dioxide makes it useful to do so.

Too-warm water isn’t the only problem—fertigation water and root zones that are too cold can also harm plants. Growers who have their plants on pots directly on the cold floor of a basement grow op or in other too-cold places risk slow root growth, decreased root mass, and ineffective root function. The same happens when fertigation water is below 65°F, and some cannabis strains will be severely damaged or even die if root zone and/or ambient air temperatures go below 59°F for even short periods of time.

A simple aquarium heater is used to warm water to the correct temperatures. When grow lights are off and grow room temperatures drop by several degrees to dip near 59-60°F, you may consider warming your root zone with grow room heat mats, rather than heating fertigation water. Most grow room heat mats are too small and generic, made for seedling or clone trays. They often lack precision temperature control—they’re either on, or off, offering no ability to program specific temperatures. Get professional size mats unless you have a very small grow space.

In all cases when you’re purchasing marijuana grow room temperature-altering gear, I recommend programable or at least digital gear that allows you to set specific, precise temperatures. This kind of gear can be hard to find, so you may have to contact several hydroponics equipment and greenhouse supply stores before you find what you need.

In all cases, I recommend placing a bubbler into fertigation water reservoirs to increase oxygenation, and using only reverse osmosis water.

As with many facets of advice about perfect growing conditions for marijuana plants, every strain is different. This means you should use the recommendations we just talked about as guides, but closely monitor your plants’ growth rate, overall health, root health, and root development to see how your temperature control strategies are working. Monitoring root development and health is easiest if you’re operating pure hydroponics systems such as deep water culture and aeroponics, of course.

If you’re growing a strain with genetic influences originating in a region with cold ambient and/or ground temperatures, you may find that a slightly lower root zone and fertigation water temperature works better than the temperatures I’ve recommended. If you’re growing a strain with genetics from hot climates, root zone and air temperatures might be best if they’re slightly higher than my recommendations. However, I caution you that fertigation water warmer than 72-72°F can create problems, no matter how heat-adapted your strain’s genetics are.

By keeping your grow room ambient air and fertigation water in the proper temperature range and by oxygenating fertigation water, you’re ensuring optimal growth, nutrients uptake, and harvest rewards from your marijuana garden. The total control that indoor growers can have over factors such as water quality, temperature, oxygenation, and root zone conditions, especially in pure hydroponics water culture systems, is a true blessing for your plants and your grow room goals.

Control your grow room air and fertigation water temperature to get bigger rewards from your marijuana growing.