Common challenges of cannabis cultivation

Growing plants for a growing industry

Growing plants can be quite simple. Giving plants adequate nutrition, water, and light, along with a comfortable temperature is usually enough to keep them alive. Surely, everyone has managed to keep a pot plant happy on their windowsill - perhaps with some trial and error. When it comes to commercial cultivation, however, businesses want their plants to thrive. Everything is optimized, from the amount of water plants receive (their ‘feeding schedule’) to plant disease prevention. For plants grown indoors, environmental conditions are controlled to ensure that plants are kept not too hot, not too cold, but just right. All of this is key to achieving the best results.

An emerging area within the agricultural industry is cannabis cultivation. The market for cannabis products is expanding, with medicinal cannabis now legal in more than 30 countries. In 2021, the total global sales of cannabidiol (CBD; an active ingredient in cannabis), medical and adult-use cannabis were over US$37.4 billion, and that number is estimated to increase to US$102 billion by 2026. While it might sound highly profitable, growing cannabis is not without challenges.

Let us discuss a few key considerations for cultivators aiming to achieve maximum yields:

To feed or not to feed – that is the schedule

Cannabis plants need a certain amount of water and particular nutrients for healthy growth and development. These needs change throughout the plants’ life cycle. Plants absorb water and nutrients via their roots. These nutrients are found in soil or can be dissolved in water which is ‘fed’ to the plants. This feeding strategy is used in hydroponics, a soilless plant cultivation method often used for growing cannabis. In hydroponic systems, nutrient-rich water is administered to plants growing in a soilless medium (like rockwool), using a watering can or automated dripper system.

Younger plants need less water, less frequently while older plants need more water, more often. If your cannabis plants are underwatered, you may notice drooping, thin leaves with curled or shriveled tips and, in the case of chronic underwatering, you may notice yellow leaves as the result of nutrient deficiencies. On the other hand, overwatering can make your growing medium waterlogged, which increases the chance of fungal infection. This can also lead to a build-up of nutrients within the plant, causing nutrient burn or browning of the leaf tips.

So how do you prevent this from happening? Enter feeding schedules that prevent over or underwatering by adjusting the volume and frequency of each feed to suit the plant’s age, pot size, and stage of development. To determine how much to feed your plants, they should be fed until the water can be seen to pass through the growing medium at the base (run-off). When determining how often to feed, methods range from low-tech solutions, such as visually noting whether the top layer of soil appears dry or the pot feels light, to high-tech systems with sensors that monitor the water content of plant media to indicate when a feed is required.

Plant pathogens and combating diseases

As you might be aware, plant pathogens reduce plant growth by causing damage to roots, leaves, and flowers. Most of the common plant pathogens for cannabis are different species of fungi (molds). One common disease is root rot. Root rot is caused by fungi and bacteria that thrive in wet conditions, and it leads to stunted plant growth, wilting, and loss of leaves in your plants.

How can you prevent root rot? You can do this by avoiding overwatering and selecting a light-growing medium that holds more air and allows water to drain easily.

If you discover white, powder-like patches of growth on the surface of the leaves of your plants, this is likely to be powdery mildew, another disease caused by fungal pathogens. Powdery mildew can cause leaves to turn yellow and dry out. To combat powdery mildew, the affected leaves should be removed, and you can use vaporized sulfur (sulfur converted from a solid to gas by burning) to reduce the spread of mildew in glasshouse conditions.

Humidity is a measure of the concentration of water vapor in the air and powdery mildew thrives under high humidity. The use of fans and cooling systems to circulate air within your indoor growing environments can ensure that humidity levels are not too high. This will also help you to prevent Botrytis, the fungus responsible for bud rot, from forming in female cannabis flowers and subsequently diminishing yields. This is crucial as these flowers produce the chemical compounds (such as CBD) that are harvested for use in treating a growing number of medical conditions.

You should also keep your indoor nurseries and production spaces separate and wear appropriate protective clothing to reduce the risk of transmitting pathogens between plants.

The case for plant tissue culture

To replicate your plants, you can take cuttings by severing branches from a mother plant. A plant rooting hormone (such as Clonex) can then be applied to the cut side of each branch before it is placed in a growing medium. This allows you to produce plants that are genetically identical (clones). The use of clones is preferred within the medicinal cannabis industry, as this helps to maintain consistency in crop yields and in the resulting cannabis products. Using this method, however, any plant pests or diseases on your mother plants may be transferred to the crop of clones.

However, using plant tissue culture, you can grow whole plants from a group of cells/tissues and produce thousands of identical clones from a single plant. By using sterile tools and environments, you can produce clean mother plants that are pest and disease-free. This reduces the likelihood of plant damage and potential crop loss. Tissue culture crops also take up less space, making it easier to store and maintain valuable genetic stock.

While there are many benefits to using plant tissue culture methods, they are not without their own challenges. Growing media and conditions need to be customized for each genotype to achieve optimal results; however, plant tissue culture possesses great potential to revolutionize large-scale cannabis cultivation. By incorporating new technologies, along with routine feeding and disease prevention, cannabis growers can improve plant health and crop yields – overcoming one challenge at a time.

For more interesting articles on different aspects of plant sciences, keep checking this space.

By Laura Steel | 19-April-2022

About the author

Laura is a Melbourne-based writer and science communicator with 4 years of experience working for an Australian medicinal cannabis company. She completed a bachelor’s degree with Honours in Biological Sciences at Monash University and is currently undertaking a PhD in plant developmental and reproductive biology with La Trobe University and the ARC Research Hub for Medicinal Agriculture.