Basic needs of a marijuana plant

Basic needs of a marijuana plant
needs of marijuana plant

A marijuana plant makes its own materials. This takes place in a process called photosynthesis.

The leaves catch sunlight and will convert it, along with carbon dioxide (CO2) and water (H2O), into sugars and oxygen.

The faster the photosynthesis takes place, the better a plant grows.

So the more light a plant gets, the more CO2 it can convert and the faster and bigger it will grow.

Outside, these elements are all naturally present. A disadvantage is that you can’t influence the climate outside.

In this course, I will teach you about the perfect environment for a marijuana plant, so that can grow as big as possible.

Indoor vs outdoor

In the open air, plants grow by themselves and require little care.

CO2 is present in the air, the sun rises every morning, and if it doesn’t rain for a while, the plant can get water deeper in the soil by using its extensive root system.

This soil is furthermore fertilized with animal droppings and dead plant material.

These are good circumstances for a plant to grow in, but it could be better.

A disadvantage of cultivating outdoors is that we can’t influence the weather.

The rays of sunlight are often blocked by clouds, it’s possible that it doesn’t rain for weeks and then for several days in a row without ending.

To achieve optimal results, the circumstances have to be perfect all the time. And this is what makes cultivating marijuana indoors so nice.

All of the needs of a plant can be better controlled and dosed.

We can provide them with exactly the right amount of water, light and nutrients.

Also, the temperature and ventilation are easy to arrange.

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CO2 is the same to a plant as what food is to humans. A plant uses CO2 to create sugars to allow it to grow and flower. So it can’t go without.

The open air contains standard sufficient CO2 for plants to grow. On average, there are 350 ppm (parts per million) of it in the air.

CO2 for marijuana plant growing
Carbon dioxide

But if you put the plants in an enclosed environment, like a grow room, they’ll consume the CO2 in no time.

Within a few hours, the value will be reduced to 200 ppm. A low value like this slows down photosynthesis, causing the plant to grow less quickly.

We want to have optimal results, so it’s important to always have a flow of fresh air that’s rich in CO2 blowing into your room.

Ideally, it should be outside air, but it’s usually also ok if you get the air from a nearby room or hallway, and open a window somewhere.

So remember that you always have to provide your plants with fresh air!


In order to absorb CO2, a marijuana plant needs light. It catches (solar) energy through its leaves, which is required to convert the CO2 into sugars.

Outside, the sun provides your plants with light, but if you grow indoors, you’ll have to light your plants yourself.

Photosynthesis process of marijuana plant
Influence of temperature

The general rule is; the more light, the higher the yield. If plants don’t get enough light, they’ll grow mainly in length and create few leaves.

And few leaves means few “solar collectors” to catch light to speed up the photosynthesis.

The spectrum of the light is just as important as the light itself. The sun has a color spectrum from red to blue, all colors of the rainbow.

Plants grow best with red and blue light because the chlorophyll absorbs the most energy at these wavelengths.

During the vegetative stage, a plant requires more blue light and during the flowering stage, it needs more red light.

In nature, these color differences are caused by color filtering of the atmosphere, which depends on the radiation angle of the sun.

Light is, therefore, bluer during spring and more red during fall. Luckily, we can buy special grow lights that meet these requirements.

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A marijuana plant is about 80% water. Everyone knows that plants die if they’re not watered.

Marijuana plants use water to transport nutrients and to cool off.

The water creates pressure on the roots and the evaporation through the leaves has a suction effect.

In this way, the plant can transport the nutrients from the soil and the created sugars in the leaves to the rest of the plant.

Problems of water resources can, therefore, cause serious damage.

Watering marijuana plants

Outdoors, in the soil, your plant generally has access to sufficient water.

The amount of rainfall is usually consistent with the needs of a marijuana plant. But if you grow indoors in small pots, your plant can dry out quickly.

Marijuana plants can use up to 1/2 gallons of water a day, depending on their size.

When a plant doesn’t have access to sufficient water, the speed of the photosynthesis inside the plant will decrease.

Also, the stomata on the leaves will close to handle water more efficiently.

This leads to less evaporation of water so the plant won’t have to absorb as much water anymore.

A result of closing the stomata is that CO2 can no longer be absorbed either.

A surplus of water has the same effects because this also slows down photosynthesis. Leaves will wilt, become yellow, wither and eventually die.

An excess of water also causes the roots to stay wet so they can no longer absorb as much oxygen, if at all.

The roots themselves are affected by the water, they’ll become softer and will eventually die.

The fine root system of a marijuana plant is in this respect very vulnerable.


Although a marijuana plant can make many nutrients itself through photosynthesis, it also needs external nutrients and minerals to optimally grow and flower.

The plant uses its roots to retrieve these from the soil. In nature, the soil contains all necessary nutrients, and it is continuously replenished by animal droppings and dead plant materials.

Indoors, we can provide the plant with additional feed in the water to prevent any shortages.

Different nutrients for growing marijuana
Nutrients for growing marijuana

These are the three most important nutrients and their function:


is crucial for making chlorophyll and proteins. The plant uses it during photosynthesis to convert CO2 into organic substances, such as sugars.

Feed that is rich in nitrogen is used for a quick growth and to create chlorophyll.

It also gives the plant a nice green color. It causes rapid cell division (increase in volume) and creates healthy leaves.


enhances the production of buds and helps the development of a healthy root system.

The weed plant uses phosphor during the entire cycle, and it needs a lot of extra phosphor during the flowering stage.

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During this beautiful stage of a weed plant, less nitrogen and more phosphor is used.

Since weed plants also need phosphor to form roots, it can also be found (in lower doses) in growth stimulators or rooting powder.


helps the immune system of the plant and increases the quality of the buds. Together with nitrogen and phosphor, potassium forms the holy trinity of every weed grower.

Just like the other two substances, it plays a crucial role in the metabolism of the plant.

It is needed for photosynthesis and for the production of proteins.

Potassium also improves the immune system, making the plant more resistant to stress, insects, and diseases.

There are ten other nutrients besides these three that contribute to an optimal development of a weed plant.

A shortage of nutrients can lead to serious problems and can greatly inhibit growth. It also affects the quality of the weed.

Luckily, the plants will immediately show when they have a shortage or surplus of a certain substance.

Leaves discolor, stems become red, growth stagnates and the shape of the leaves changes.

Limiting factor

f all these factors are optimally present, your marijuana plants will grow as large as possible. But there’s always a limiting factor.

This is the factor of which the value is furthest away from the optimal value.

Let’s say you have a 250-watt lamp, there’s sufficient CO2 in the room (350pp, just like outside) and the plant gets enough water and nutrients.

The light will then be the limiting factor. Because if you use a 400-watt lamp in these circumstances, you can almost double your yield.

And you can harvest even more with a 600-watt lamp.

But if you use a 1000 watt lamp, the plant will need more CO2 than standard air can provide, causing CO2 to become the limiting factor.

The plant can’t convert all the energy from the lamp because it needs more CO2 to do so.

This is how all factors are connected and influence the functioning of a plant.

Depending on the stage the plant is in, these values slightly differ, but generally speaking, these are the perfect values;

growing marijuana outdoor
Growing marijuana

Bergman’s Numbers

Environmental factors

  • Light: 600 watt per 12 ft2
  • Temperature: 77 degrees F
  • Humidity: 50-60%
  • Water: as required
  • CO2: 350 ppm
  • Nutrients: 1.0 to 2.0
  • pH: 6.0

Again, these values depend on the stage the plants are in.

Seedlings can’t take as much feed as older plants, and they’ll evaporate more and more water as they grow, so you’ll have to water them more.

In the next section you’ll learn how a marijuana plant converts light into energy and how it absorbs and transports nutrients.

If you have any questions, please ask some fellow growers or one of our grow experts on forum.