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

plant water temperatureWhen 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.

plant water temperature

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.

Cannabis seedling

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.

Hydroponic cannabis grow

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.plant water temperature

plant water temperature






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!

Generic selectors
Exact matches only
Search in title
Search in content

9 replies on “Plant Water Temperature for Cannabis”

silly question on my part but would like clarification. Is that 20 degrees Celsius or ferinheight? I’m going to assume Celsius since water freezes at 32 degrees ferinheight. Thank you for your assistance.

Hi Daniel!

You’re right, it’s in Celcius – we’re based in Europe. Sorry for the confusion, we usually clarify with C or F, but it seems to have slipped by this time. I’ll add it right away, thank you!

Thank you !!!!!! I’ve been looking all over for an article on this. 3 weeks in and my plants just took a turn for the worst it looks like. New plants are getting spotty leaves and looks like cal mag. Purple on tops. Slowed growth. The plants I water in the day are crushing and happy. The ones I watered w the water I am using outside in a bucket is getting down to 55f. 14c I think. This is my problem. I’m not getting uptake, looks like lock out. Even after a flush, it’s still is happening and I’m pretty convinced it’s the temp after reading this article. Thank you in advance if this works. I’ll try and check back In.

Hi, I just bought a water heater and it’s not adjustable it’s locked at 25c will this be a problem for my hydro set up, or should I just buy another one to keep the temp at about the 20-22c mark, thanks.

Hey Glenn
If you have a timer you can set it to turn for short periods of time on at intervals (every 15 minutes, for example) & test it out to see if you can keep it below 23°C. If not, you may need to get another one as 25°C is a bit excessive, especially when growing in hydro.

Hi! I heard somewhere I need to ceap temperature between 19/20c and I doing that. Or it’s a problem? My all seems and leaves are strong and showing no issue just all steems ar purple, or this is because of water temperature?

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.

Leave a Reply

Your email address will not be published. Required fields are marked *