As is the case with all life on earth, marijuana plants need water to survive.  Likewise, the key to healthy and resilient cannabis plants lies in careful balance. Just like human beings, too much or too little water can kill a cannabis plant in days.

Somewhere in the region of 80% of a marijuana plant is comprised of water.  Along with providing much of the plant’s structural integrity, this precious fluid is also responsible for nutrient transportation. Not to mention, essential temperature regulation.

In most instances, the catastrophic consequences of too little or too much water become quickly evident. But despite the whole thing being one of the most basic fundamentals of cannabis cultivation, millions of growers find it difficult to draw the line.

How Much Water Do Cannabis Plants Need?

This may be the most obvious question, but it’s also the most difficult to answer. The reason being that there is no specific rule as to how much water cannabis plants need. Or for that matter, when they need it.

For one thing, requirements vary enormously from one cannabis strain to the next. If a strain originates from a region where conditions are moist throughout the year, they’ll naturally need plenty of water to thrive. By contrast, if the strain originates from an arid environment where rainfall is minimal, considerably less water is needed.

In addition, the size of your marijuana plants will play a role in determining how much water they need. If watering just a couple of Purple Afghan Kush plants measuring 30cm in height, you’ll hardly need as much water as when dealing with 10 Malawi Gold plants at a towering 3m+ in height.

Then of course there’s the matter of your chosen growing medium. If using fast-draining soil, water needs to be added on a more regular basis. At the opposite end of the scale, clay soil doesn’t drain nearly as fast and is prone to becoming waterlogged. From soilless mixes to hydroponics and everything in-between, water quantities must be varied to accommodate specific growing mediums.

When Do Marijuana Plants Need Watering?

Once again, concrete rules for effective watering simply don’t exist. Instead, it’s a case of familiarising yourself with the signs and signals of a plant’s requirements. For example, if the lower foliage of a cannabis plant shows any signs of slackness, it’s clearly in need of a good drink. Of course, it’s never a good idea to let things get this far – doing so risks irreparable damage.

In most instances, water should be carefully added when the soil feels dry to a depth of around 5cm. Rather than watering the moment the surface appears dry, use your finger to gauge moisture levels to around this depth. When adding water, try to avoid soaking the stem, as doing so can increase the risk of stem rot.

Over time, you’ll come to know if and when your cannabis plants require more water. Varying water quantities during your grow being essential, due to variations in plant requirements and atmospheric conditions.

Overwatering and Underwatering Cannabis Plants

Underwatering can destroy a cannabis plant, though is a surprisingly rare issue. This is because it’s easy to recognise an issue with insufficient water, which can also be immediately corrected by adding more water. If any foliage starts to droop or sag, you’ve limited time available to water the plant and repair the damage.

By contrast, overwatering is the single most common error when cultivating cannabis. Excessive quantities of water prevent the roots from absorbing the oxygen and nutrients the plant needs to survive. The problem being that by the time the problem is identified, the damage caused can be irreparable. 

Hence, it’s better to err on the side of caution, only watering when you’re sure you need to.

The Best Water for Marijuana Plants

Along with providing the perfect amount of water, it’s also worth considering water quality. In most instances, everyday tap water is more than good enough to get the job done. Nevertheless, if chlorine or any other toxic substances are present, filtration could prove beneficial.

In an ideal situation, water for marijuana plants must fall between a pH of 5.6 and 5.8 during the vegetative stage, increasing to a range of pH 6.0 to 6.2 while flowering. Increasing oxygen concentrations in the water can also be helpful, boosting root health and the general performance of your cannabis plants.


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