Watering Marijuana Plants

Life isn’t possible without water. Water contains dissolved nutrients and can be absorbed through the roots. It circulates through the entire plant and transports nutrients to the leaves. It fills the cells, causing the plant to stand up straight. It evaporates through the stomata to cool the plant and it makes sure the plants can withstand the powerful rays of sunlight without burning. Only 1 percent of the water is used by the plant for photosynthesis, by binding it with carbon dioxide.

As you can see, water is very important to marijuana plants. That’s why it’s important for you to learn how much you should water your plants. The most important thing is to regularly check your plants to see if they need water. You can get a good sense of the water usage of your plants by weighing them. In this chapter I’ll teach you when, how much and how you should water your plants.

When to water

Increasing the temperature in your growing room
Increasing the temperature

Always water your plants in the morning or when the lights come on. Photosynthesis doesn’t take place during the night and the plant doesn’t evaporate any water without light. If you water the plants right before it gets dark, the roots will be too wet and too cold all night, since no water is being absorbed. During the flowering phase this can lead to bud rot because the humidity will become too high.

It’s not a big deal if this happens once or twice, but if you want to do it perfectly, you should water the plants when the lights are on. The ideal time to water your plants is when the lights have been on for an hour. The evaporation process will be up and running at this time, so your plant can absorb the water right away and transport it through the entire plant.

How much to water

Watering marijuana
Much more water

There’s no standard answer to this question, because one plant uses more than the next. A plant that receives a lot of light and has proper evaporation will use much more water than a plant that doesn’t get as much light. I will give you an example about the amount of water I gave my plants I used for this course.

I always water them on Mondays, Wednesdays and Fridays. I made this schedule because I often grew on locations I didn’t have access to in the weekend. If you just start growing, it’s best to check your plants every day to see if they need water. But this is what I give my plants;

  • Seedlings: 1/16 gallon per watering per plant
  • Start of growing stage: 1/8 gallon per watering per plant
  • End of growing stage: 1/4 gallon per watering per plant
  • Start of flowering stage: 1/2 gallon per watering per plant
  • End of flowering stage: 1 gallon per watering per plant

I usually give them a bit more on Fridays, because they have to go without water an extra day.

Weighing your pots

You have to get a feel for the water use of your plants. You can do this by feeling or weighing your pots every day. Fill a pot with soil and feel how heavy it is. Fill another pot with soil and now slowly fill it with water until it starts coming out the bottom. If the water runs out the bottom, the soil can’t absorb any more and it’s saturated. You now have two pots with soil, one with water and one without.

The first pot is too dry, so the plant can’t absorb any water and nutrients. The second pot is too wet, causing the roots to suffocate and rot. This doesn’t happen until they’ve been too wet for over a week. Lift both pots and feel the difference. You have to end up with a bit above the average weight for a perfect water/soil ratio.

You could also weigh the pots in the beginning to get a sense of the amount of water you need to give. You’ll also see that one plant uses more than the next. You should therefore feel the pots every day to see if they need to be watered.

Watering outdoor plants

Watering outdoor plants
Outdoor plants

Plants that are outside can survive solely on rain water. But they can experience difficult times if they’re in a sunny spot and it hasn’t been cloudy for days. To get a sense of the dampness of the soil, you can apply the tip I mentioned above. Take a bit of soil from around your plant when it’s dry and weigh it. Then, let it absorb as much water as possible and weigh it again. Now weigh the same amount of soil during dry days to check the humidity.

You’ll see that you can quickly tell from the soil if your plant needs water. So check the weather forecasts and make sure your plants are never too dry. If outdoor plants get enough sunlight and always have access to water, they can really turn into massive bushes.


Not enough water marijuana plant
Day 5 no water

Overwatering your plants is one of the biggest mistakes you can make, usually made by novice growers. The roots get way too wet and they can no longer absorb oxygen and they’ll eventually die off. The chance of fungi also increases when your soil is too wet.

The consequences of overwatering are yellow leaves that fall off, and sometimes leaves that aren’t yellow will fall off. The leaves will start to wilt, just like in case of under-watering. But if you just watered your plants and you have wilting leaves shortly after, it’s definitely not from under-watering…

Prevent overwatering by getting a good feel for your plants and by feeling and weighing your plants every day in the beginning. And don’t water your plants for a bit if they’re too wet.


Plants that get too little water show the same symptoms as plants that get too much water. This is because in both cases the evaporation stops and the plant closes its stomata. The leaves turn yellow and will start to droop. Photosynthesis will slow down and the plant will eventually die.

Wilting plants can be easily restored by watering them again.

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Robert Bergman

Robert Bergman is an Amsterdam-based marijuana grow expert who has years of experience from small grows to massive operations. His passion for growing lead him to develop his own Gold Leaf strain. Now, Robert is dedicated to sharing his knowledge with the world.... [Read full bio]

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