All about marijuana irrigation

El riego del cannabis

Through our social networks we are frequently asked about the best way to water our cannabis plants and which type of water we advice. In this article we are going to solve the mystery!

We all know that an adequate watering is very important for the health and development of our cannabis plants. Throughout the process of growing cannabis, the water intake raises while the plants are developing.

Cannabis is a plant that needs a lot of water but, at the same time, it does not deal well with excess of water, so it is very important to know the correct way and the adequate moment to water your plants.

Let’s start with the basics!

What is watering?

Watering is the action or spreading water over the soil or surface with the goal of refreshing or cleaning it, contributing with hydration while feeding the plant. Yes, you got it right!

Spreading water over the soil is not the same as flooding the pot. Now that we know the difference we are going to use the knowledge in a cannabis grow operation.

First step: What is the most adequate water for your cannabis plants?

A lot of growers ask this question. There are different options and all of them can be correct if we do it in the right way.

These are the options:

    Agua para riego

  • 1.- Using tap water may be a good option. It is the easiest and most economic way of watering your plants. But, in the long run, it can become the most expensive option because of several factors which, for excess or defect, can not be controlled, such as chlorine, calcium, magnesium and other elements like bacteria.

    How can we solve this problem? You can mix your tap water with 70% of distilled water, so that it can compensate for all the harmful substances present in tap water. Besides that, it is important to let it rest in an open container for at least 24 hours so that the chlorine (or a good part of it) can evaporate.

    If you chose this option it is very important to control the pH and EC levels of the water to check if they are adequate for watering.

    As we speak of watering cannabis plants, the water should be as clean as possible.

  • 2.- Some growers prefer to use rain water. Rain water, as its name indicates, is collected when it rains. Once it is collected it has to be sterilized to dump off the abundant bacteria, fungi and other elements that it usually contains, such as acid gases. How do we sterilize it? It is very easy: you just have to boil it for a few minutes.

    By boiling we can eliminate the microorganisms from the water and, through filtration, it is possible to eliminate all types of bacteria, fungi, etc. With this you have it ready to use in your next watering.

    Attention! You should always take into consideration that there are many differences between tap water and rain water. Rain water is more acid, its pH stands between 5,5-5,6 and, as it is in permanent contact with carbon dioxide from the air it tends to be much more contaminated than tap water.

    In conclusion, if you choose this option don’t forget to also measure the pH and EC levels from the water.

  • Tipos de agua para el riego

  • 3.- Other alternative to water your plants is bottled or reverse osmosis water. Neither of these options require a special previous treatment, because they already passed through several quality filters. They are sterilized and ready to be used to water your plants. Besides that they usually have a pH standing between 6 and 6,5. That is a very good score!

    If you kept reading until this point, you can already choose which type of water you prefer for your grow operation.

    And yes, we insist: never forget to measure the pH of the water that you are going to use to make sure that it stands between 6 and 7, whether it is tap water, rain water, from reverse osmosis or bottled.

Second step: how to accomplish an adequate irrigation

  • Water your plants in a correct way: The best scenario for the health of your plants is a point of equilibrium between a dry and a humid growing medium. If the soil is humid, give it a bit more time to dry out. Cannabis is a very strong plant and can resist a few more days until the soil is completely dry, to only then be watered again.

    Following these steps you can respect the “dry-humid-dry” cycle, which is very important as it allows the roots to “breed”.

  • Check the PH and EC levels: We already talked about it a few paragraphs before. It is very important to know the level of concentration of salts in the water that you use to water your plants. The EC allows you to measure the amount of fertilizers that are dissolved in the water: the calcium, chlorine, etc. It helps you to control the feeding of your plant so that you can avoid under or overfeeding your plant. The correct values of EC stand between 0,4 and 0,8.

  • Water your plants correctly: Slowly and always paying close attention. You should always have time to water your plants so that you don’t need to do it quickly. It is advisable to water in small amounts instead of using a lot of water. Let your plant breath and NEVER drown it!

    On the other hand, in high temperature climates, it is recommended to water by night. This is because if we do it during the day, the roots could get diseases and mold.

    Instead, if the climate is soft or moderate, the time of the day is not important because we will always have an optimal temperature in the roots to water the plants. The optimal temperature stands between 18 and 24 ºC in a soft or moderate climate.

Regar plantas de marihuana

Third step: how to water according to the stage of the grow operation

In the first step of the grow, germination, there is no watering at all. The seeds are germinated between paper towels previously sprinkled with water.

The paper towels don’t have to be too wet! If they are too wet a lot of bacteria could proliferate and rotten the seeds.

The sign to identify the next stage of the grow operation is when the first root of the seeds appears, with approximately 1 cm. In that moment, we humidify the soil before planting the seed in it for the start of the growth stage.

Watering in the growth stage

During the second stage, known as growth or vegetative stage, it is important to take into consideration several factors:

  • Check if the growing medium is not swampy: before watering your cannabis plants check if the soil is not too humid or even swampy. If the soil is swampy or too humid the roots will not get enough oxygen and will be more exposed to the proliferation of bacteria.
  • Develop a strong root system: this is only possible if you water with a good frequency but not every day and always considering the previous point.

These two factors are very important when it comes to keeping the soil airy, allowing the plant to breathe.

Watering during the flowering stage

Once the plant enters the flowering stage its root system should be strong and well developed. For this, you will have to water the plants more often and make sure that the soil is always humid.

In this stage, the cannabis plant is bigger and is able to absorb a greater amount of water.

How do we measure the amount of water?

Each plant is unique, so it depends on multiple factors such as the size of the plant, type of soil, the size of the pot, etc. Anyway, we recommend that you use between 250 ml and 500 ml of water during the first four weeks of flowering if you use a 10 litre pot.

As we already told you, during the first weeks of the flowering stage the plant has to absorb a higher amount of water. But, after the fifth week, we have to reduce the amount of water as the soil tends to keep humid for a longer time.

When the plant gets to the final cycle of its flowering, the roots are partially deteriorated. With this they don’t adequately absorb the water or nutrients and the soil tends to remain humid for a longer time.

El riego de marihuana

Watering close to harvest

A good flush is a very important step that should be performed a couple of weeks before harvest. This root wash process must be done only with water (no fertilizers) and during the last two weeks before harvest. In this way, we manage to eliminate the nutrients that are accumulated in the soil so that the plant uses the nutrients stored in its own tissues.

Once the plants reach to their final stage, harvest, they need to consume less water and, therefore, it will be necessary to progressively reduce the amount of water used in each irrigation. If the plant has to deal with too much water in the soil, the chances of developing mold in its buds will increase.

And to finish, we would like to remind you of an important fact in the irrigation of autoflowering plants: their size must be taken into account.

Watering autoflowering plants

For autoflowering plants there is an handicap: their size. Why? They grow faster! They start flowering according to their age. They usually start flowering when they reach to approximately 3 weeks of age, so controlling the waterings is essential for a strong and healthy growth.

If we water with excess water we can cause some kind of stress and the plant may become smaller than it should be. To prevent this from happening, we will have to water the plants in small amounts and always avoid to do it when the soil is wet.

And now we are finally getting to the end! Here is a summary of the most usual errors that you should avoid when you water your plants:

  • Using plates under the pots: The roots may get mold and this would negatively affect the development of the plants.
  • The temperature of the water: In the summer the water left under the hot sun easily gets to high temperatures and should never be used to water the plants. In the winter the ideal water temperature stands between 18 and 20 ºC. Not too cold and not too hot!
  • Clay pots: These are not advisable for growing cannabis because they are heavier than plastic containers and so it is much harder to check if there is still water in the soil by weighing the whole thing.
  • Watering the plants every day: Watering control. You only have to water every day in very specific situations, such as in outdoor grow operations during the hottest stage of the year and only if the soil dries out in 24 hours.


Now that you already know the different types of water, in what measure the waterings should change according to the stage of the life cycle of the plants and the most usual errors that growers do when they water their cannabis plants… we hope that you can successfully apply this knowledge in all your grow operations.

Sweet smokes!

Sweet Seeds S.L is not responsible for the misuse of the information contained in this article. Cultivation of cannabis may constitute a criminal offence or administrative misdemeanour; please refer to the legislation on cannabis in your place of residence. Sweet Seeds S.L. does not intend in any case to incite non-legal practices.


Texto: @Sweet Seeds®