Knowing how marijuana plants absorb water and nutrients is not only fascinating but also enlightening. You see, the more you understand the processes involved, the better you can optimize the conditions. Its ramifications, of course, are better overall bud quality and yields.

What Happens During Photosynthesis?

Before delving into the mechanisms involved in the absorption of nutrients and water, let’s begin with photosynthesis. Chlorophylls – better recognized as being responsible for the color of leaves – perform a more critical function. These green pigments also act as solar panels that collect light from the sun (or any artificial lamp used in an indoor setting).

The plants use light as an energy source, converting 6 water (H2O) molecules and carbon dioxide (CO2) molecules into 1 sugar and 6 oxygen (O2) molecules. They then use the sugars created to grow in mass and release excess O2 into the atmosphere. The use of CO2, in more ways than one, is how plants help regulate CO2 – a greenhouse gas – in the atmosphere.

How Do Plants Get Carbon Dioxide, Water, and Nutrients?

Clearly, marijuana plants need CO2, water, and nutrients to carry out photosynthesis. How they absorb each of those necessary ingredients to create sugar is a fascinating read. In a nutshell, they are absorbed through the leaves and through the root system.

Carbon Dioxide

Stomata are tiny pores found mostly on the surface of leaves. They are also on other green parts, such as stems. Each stomatal pore is surrounded by two guard cells responsible for its opening and closing.

During photosynthesis, water flows into the guard cells, causing them to swell. Consequently, the pore opens up as the cells begin to curve. It is through this opening that the plants absorb CO2 from the atmosphere. Remember that when there is light, there is heat. The plants also lose water through the open stomata.

In the dark period, photosynthesis stops. By then, there is less water in the guard cells. The stomatal pore closes as the pair of cells straighten. Under normal circumstances, the plants no longer need CO2 since there is no energy to convert them, along water and nutrients, into sugars. But that could also happen during “daytime” as self-preservation means should the plants experience a drought, in which they need to conserve water.


Although the root system is credited for absorbing water, know that practically all parts of plants can do that too, such as leaves and stems. It’s important to prepare the best water for your cannabis plants full of nutrients to help your plants grow.

So, how does it happen?

Root hairs are outgrowths of the epidermis – the outer layer of root tissue. These thin-walled unicellular hairs are in contact with water molecules found in regularly drenched soil.

Think of the root hairs’ cell walls as semi-permeable membranes, on which molecules could pass through. On either side (outside and inside the roots), there is a pressure exerted.

Because the soil solution has less pressure than in the cell sap of the root hairs, osmosis occurs when water molecules move from the soil into the plants through the cell walls of root hairs.

Above ground, osmosis also occurs on the leaves and other parts of the plants. For you to understand this process, imagine a container filled with water. It has a semi-permeable membrane that separates the water into two sections.

On either side, water molecules are in constant motion. They bump into each other or the surface of the container and the membrane. The total force exerted by the collisions is called pressure. Because there are tiny openings on the barrier, some molecules pass through one side to the other and vice versa.

Now, imagine if you were to add a substance to one side of the container. Salt, for example. That side would now have more particles (salt and water molecules). Assume that the salt molecules are too large to pass through the tiny holes. In this scenario, there will now be fewer water molecules passing to the side that only contain pure water. On the contrary, the salted side would receive more water molecules.

Based on the above example, osmosis, thus, can be defined as the net movement of molecules from a region of lower solute concentration to a region of higher concentration.

Cell saps have a higher solute concentration, so water from the soil moves into the root hairs. That also happens on the surface when the leaves absorb moisture from the air through open stomata.


Marijuana plants comprise up to 90% water. Through transpiration, they lose water to the atmosphere. Meanwhile, beneath the ground, the root system continues to grow and spread all over. As water leaves the plants, a suction effect is created, resulting in nutrients that are in contact with the roots being absorbed and transported up to the leaves.

As you can see, it is not like the plants can determine which nutrients to absorb. It is why you should be mindful of using the right nutrient mixture, ratio, and dosage to avoid nutrient burns.

A Beautiful Thing: Photosynthesis and Osmosis

When talking about water and nutrients – and how plants absorb them, it is impossible to disregard light, CO2, and photosynthesis. Quite simply, they are intertwined, and the processes in which it works is a thing of beauty.

Light drives photosynthesis. But for that process to happen, the other ingredients must also be available. As you learned, the plants could absorb moisture and CO2 from the atmosphere through stomata. It is also through those openings that the plants lose water and expel unused oxygen. Ensure you maintain a good watering schedule for your cannabis plants throughout the grow cycle.

Meanwhile, through osmosis, the plants can keep themselves hydrated, absorbing water. But as they try to keep their temperature in check, the loss of water above ground causes a suction effect that results in the roots absorbing minerals from the soil.

Poetry in motion. That is the best way to describe all those parts involved, their individual roles and functions, all meshing together to do one thing – create sugars. It is food for them to grow – to keep developing more stems and leaves as they increase in mass. More importantly, that turns into bud and THC production once the bloom stage begins.

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