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Over-watering cannabis plants

Over-watering and under-watering cannabis plants

Watering cannabis plantsOver-watering is the single biggest mistake made by beginner growers. It leads to the roots becoming too wet and thereby unable to take up enough oxygen, thanks to which they will slowly die.

The characteristics of over-watering are primarily yellow leaves that fall off, and sometimes not yellow leaves falling off too, leaves that droop (just as in under-watering) but if you’ve just given them water and they continue to droop then you can be sure the cause was not under-watering!

You can avoid over-watering by doing this: when your soil is dry, lift up your pot and weigh it, then weight it again when you’ve fully watered it. If you repeat these weighings for a day or two then you’ll have an accurate idea of how much water the plant is using and develop a better idea of how much to give her!

Learn more about watering correctly here.


Under-watering can produce the same symptoms as over-watering, but that weighing method above will allow you to determine which one is happening.

With under-watering you’ll notice that the leaves hang closer to the stem and they will also droop harder! Many will claim that when they can see a few drops flow out the bottom of the pot, that’s the perfect dose of water, but I personally try to avoid this. But things can vary from pot to pot!

The tensiometer:

Ground water can be very accurately determined by measuring the soil water tension.

Water tension, or  ‘suction’ can be measured with a tensiometer, and it will be indicated in hPa. A tensiometer is in fact no more than a hollow tube with on the underside a sort of porcelain lump attached to it. On the top is a meter that reads off the water tension.

tensiometerWhen there is too much water in the soil and therefore the big spaces between the soil particles are filled with water, the plant will try to take this up as quickly as possible.

When there is little water in the soil and therefore only the small spaces between the soil particles are filled with water, then the plant will have to exert more "effort" to take the water up.

When there’s too much water in the soil the particulate matter can no longer retain and more water and any further drains, as the soil is saturated.

When there’s too little water in the soil then too great a suction has to be used to get water out of the soil and the plant is no longer able to absorb the remaining water. This is the withering point.

Water balance in the soil

• 0 hPaA

suction of 0 means that the soil is completely saturated. This is to be expected after a large irrigation. If the suction remains at 0 for a long period, the roots of the plant can become deficient in oxygen and become ill.

• 0-50 hPa

If the suction is between 0 and 50 hPa there is an excess of water for the plants present. This suction level is common after irrigation.

• 50-200 hPa

A suction in this range means that there is sufficient water and air in the soil for optimal plant growth.

• 200-400 hPa

The suction is good for plant growth in a soil with a normal or fine structure, but in a sandy soil the suction can rise rapidly thanks to which there will be a water shortage.

• 400-600 hPa

The suction is good for a soil with a fine structure. But in other soils the suction can rise rapidly thanks to which there will be a water shortage.

• 600-800 hPa

The water available for the plants is scarce. Also, in a soil with heavy clay the suction can rise quickly and create water scarcity. Note that a reasonable percentage of clay in your medium will always be of benefit to our favourite plants.

This is a rough indication of the soil conditions for a plant. In practice the soil condition is dependent on the type of soil and its structure. In addition, one plant variety is more sensitive to drought than the other. Thanks to this the best time to give water will vary from user to user.

If you have used a tensiometer the perfect suction value is 80hPa, so try to keep your soil as close to this as possible!

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