Cannabis Nutrients And Deficiencies
Growing cannabis isn’t always a walk in the park. One of the more common issues that growers face is small yields due to nutrient deficiencies. These occur when your plants aren’t getting the right balance of nutrients, which can lead to stunted growth, yellowing leaves, and ultimately, a less-than-great harvest.
In this comprehensive guide, we’ll be diving deep into the world of cannabis and nutrient deficiencies. We’ll cover everything from understanding your plants’ nutritional needs to identifying common deficiencies and implementing effective prevention and treatment strategies.
Understanding Cannabis Nutrient Needs
Before we get into the nitty-gritty of nutrient deficiencies, it’s crucial to understand what nutrients plants actually need to thrive. Just like humans, all plants require a balanced diet of macronutrients and micronutrients to grow and develop properly.
The 3 Main Macronutrients That Cannabis Plants Need Are:
- Nitrogen (N): Nitrogen is essential for leaf growth and chlorophyll production. It’s especially important during the vegetative stage when plants are focused on developing a strong canopy and healthy leaves.
- Phosphorus (P): Phosphorus plays a vital role in root development, stem strength, and flower production. It’s most critical during the early flowering stage when plants transition from vegetative growth to bud development.
- Potassium (K): Potassium is responsible for overall plant health and although it is listed 3rd it is actually the 2nd most important macronutrient, responsible for disease and stress resistance, and the production of terpenes and cannabinoids. It’s important throughout the entire growth cycle, but especially during the flowering stage.
In addition to these macronutrients, cannabis plants also require smaller amounts of micronutrients such as calcium, magnesium, iron, and zinc. While they’re needed in smaller quantities, they’re just as important for proper plant development and overall health.
It’s essential to provide your plants with the right balance of these nutrients at each stage of growth. During the vegetative stage, plants require higher levels of nitrogen to support leaf growth and chlorophyll production. As plants transition into the flowering stage, their phosphorus and potassium needs increase to support bud development and overall plant health.
Using a good nutrient rich living soil is the best way to buffer your plant long term against any nutrient deficiencies, however, over time the nutrients of any potted plant will need replenishment. Autoflowers have a limited life span so they are far more forgiving when planted in a good growing medium compared to photoperiodic plants.
Common Cannabis Nutrient Deficiencies
Now that we have a basic understanding of what nutrients cannabis plants need, let’s take a closer look at some of the most common nutrient deficiencies and how to identify them.
1. Nitrogen Deficiency (N)
Nitrogen deficiency is one of the most common issues that cannabis growers face. It typically starts with the lower leaves turning pale green or yellow while the upper leaves remain green. As the deficiency progresses, the yellowing will move up the plant, and the leaves may start to fall off.
Symptoms of nitrogen deficiency include:
- Stunted growth
- Thin, long, weak stems
- Reduced flower production
If you do notice signs of nitrogen deficiency, you can try the following remedies:
- Apply a foliar spray of fish emulsion or seaweed extract like biobizz fish mix
- Top dress your soil with organic nitrogen sources such as worm castings, live earthworms, blood meal, or bat guano
- Increase or use nitrogen-rich supplements during the vegetative stage. Look for fertilizers with an NPK ratio that has a higher first number (nitrogen) compared to the other two numbers (phosphorus and potassium). Eg 5-2-3
2. Phosphorus Deficiency (P)
Phosphorus deficiency can be a bit trickier to identify, as the symptoms can vary depending on the stage of growth but it is a rarer problem by comparison. In young plants, phosphorus deficiency can cause stunted growth and dark green or brownish leaves. In flowering plants, it can lead to small, underdeveloped buds and a general lack of vigor with yellow and brown spots on older growth. The leaf will start to die and change in colour first either by turning yellow or brown all along the leaf edges.
Symptoms of phosphorus deficiency include:
- Thin, weak stems
- Reduced root growth
- Increased susceptibility to pests and diseases
To prevent phosphorus deficiency, make sure you’re using a fertilizer with a higher phosphorus ratio during the early flowering stage. Look for fertilizers with an NPK ratio that has a higher second number (phosphorus) compared to the other two numbers (nitrogen and potassium). Eg 3-7-4
If you do notice signs of phosphorus deficiency, you can try the following remedies:
- Apply a foliar spray of seabird guano or bone meal tea
- Top dress your soil with organic phosphorus sources such as rock phosphate or bone meal
- Increase the amount of phosphorus in your nutrient solution
Note: It is a common mistake for growers to try supplement phosphorus. High levels of soluble phosphorus can decrease microbial life and stunt root development so it comes with its own problems. Most balanced fertilizers for both the veg and bloom stage contain phosphorus so deficiencies are fairly rare.
3. Potassium Deficiency (K)
Potassium deficiency is probably the most difficult to identify but typically starts with the lower leaves turning yellow or brown unevenly around the edges while the center of the leaf remains a healthy green. As the deficiency progresses, the yellowing will move up the plant stem, and the leaves may start to curl or twist from all sides which is normally its tell tale sign. If you think you have a potassium deficiency in the vegetative stage you are likely mistaken as this deficiency is most commonly associated with the flowering phase.
Symptoms of potassium deficiency include:
- Weak, brittle stems with a shorter internodal space
- Dark and over green leaves in the veg stage
- Uneven yellow or brown leaves starting from the bottom of the plant
- Brown curling and dead spots throughout all the edges of the leaf not just the tips
- Reduced flower size and bud production
- Increased susceptibility to pests and diseases
- More frequent waterings are required and heat stress symptoms show
To prevent potassium deficiency, make sure your growing medium does not have too many salts or sodium in it and use a fertilizer with a balanced NPK ratio from the start as this is a slow moving nutrient and required throughout the entire growth cycle especially in the flower stage. Look for fertilizers with an NPK ratio that has equal numbers for all three nutrients or close, and follow their instructions.
If you do notice signs of potassium deficiency, you can try the following remedies:
- Apply a foliar spray of kelp extract or wood ash tea
- Top dress your soil with organic potassium sources like a 1:20 wood ash and water solution
- Increase the amount of potassium in your watering nutrient solution
4. Calcium Deficiency (Cal)
Calcium deficiencies can cause a variety of issues like curled or cupped leaves, and brown or yellow blotches coupled with stunted growth. In severe cases, it can even lead to bud rot or other fungal infections.
Symptoms of calcium deficiency include:
- Brown blotches and yellowing leaves
- Weak, brittle stems
- Curdled drooping leaves
- Slow root development and growth
- Bud rot
To prevent calcium deficiency, make sure both your soil and water are within the correct PH range. PH Issues are the main cause of calcium uptake deficiencies even when using a calcium-rich supplement such as cal-mag. You can also try adding crushed eggshells or sea shells to your soil mix although these take a long time to break down and won’t be a short term fix.
If you do notice severe signs of calcium deficiency, you can try the following remedies:
- Apply a foliar spray of calcium chloride or calcium nitrate
- Top dress your soil with PH balanced gypsum or dolomitic lime solution
- Increase the amount of calcium in your nutrient solution
5. Magnesium Deficiency (Mg)
Magnesium deficiency typically starts with the lower leaves turning yellow between the veins while the innerveins themselves remain green. As the deficiency progresses, the yellowing will move up the plant, and the leaves may start to curl or twist.
Other symptoms of magnesium deficiency include:
- Stunted growth
- Reduced flower production
- Increased susceptibility to pests and diseases
To prevent magnesium deficiency, make sure your coco coir is properly buffered with Cal Mag before planting anything in it. Read more here (*) You can also try adding dolomite lime or epsom salts to your soil mix.
If you do notice signs of magnesium deficiency, you can try the following remedies:
- Apply a foliar spray of Epsom salts or magnesium sulfate
- Top dress your soil with Epsom salts or dolomite lime
- Increase the amount of magnesium or cal mag in your nutrient solutions
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Preventing Nutrient Deficiencies
While it’s important to know how to identify and treat nutrient deficiencies, it’s even better to prevent them from happening in the first place. Here are some tips for preventing nutrient deficiencies in your cannabis plants:
- Start with good genetics: Choose easy to grow strains that are known for being hardy and resilient. Avoid strains that are untested or prone to nutrient deficiencies or other issues.
- Use a high-quality grow medium: Invest in a high-quality, nutrient-rich soil mix that’s specifically designed for cannabis. Look for soil mixes that contain organic matter such as compost, worm castings, and perlite for improved drainage and aeration.
- Monitor pH levels: Make sure your soil and watering solution stays within a general pH level of between 6.0 and 7.0. Imbalances can prevent your plants from absorbing nutrients properly, even if they’re present in the soil or water.
- Use the right fertilizers: Choose fertilizers that are specifically designed for cannabis and follow the manufacturer’s instructions carefully. Never overdo it with the nutrients, as this can lead to nutrient burn and other issues.
- Keep an eye on environmental factors: Make sure your grow room has proper ventilation, humidity levels, and temperature control. Extreme environmental conditions can stress your plants and make them more susceptible to nutrient deficiencies.
- Implement a regular feeding schedule: Consistency is key when it comes to feeding your plants. Develop a regular feeding schedule based on your plants’ growth stage and stick to it as closely as possible.
- Use organic amendments: Incorporating organic amendments such as compost, bat guano, worms and worm castings into your soil mix can help provide a slow-release source of nutrients throughout the growing cycle.
In addition to these macronutrients, cannabis plants also require smaller amounts of micronutrients such as calcium, magnesium, iron, and zinc. While they’re needed in smaller quantities, they’re just as important for proper plant development and overall health.
It’s essential to provide your plants with the right balance of these nutrients at each stage of growth. During the vegetative stage, plants require higher levels of nitrogen to support leaf growth and chlorophyll production. As plants transition into the flowering stage, their phosphorus and potassium needs increase to support bud development and overall plant health.
Using a good nutrient rich living soil is the best way to buffer your plant long term against any nutrient deficiencies, however, over time the nutrients of any potted plant will need replenishment. Autoflowers have a limited life span so they are far more forgiving when planted in a good growing medium compared to photoperiodic plants.
Homemade Remedies and Amendments
In addition to commercial fertilizers and supplements, there are several homemade remedies and amendments that you can use to prevent and treat nutrient deficiencies in your cannabis plants. Here are a few of our favorites:
Compost Tea:
A compost tea is a great way to provide your plants with a quick boost of nutrients and beneficial microorganisms. To make compost tea, simply hang a small meshed bag of compost in aerated water for 24-48 hours, then strain and apply to your plants as a foliar spray or soil drench.
Eggshell Powder:
Eggshells are an excellent source of calcium and can help prevent calcium deficiencies in your plants. To make eggshell powder, simply collect and rinse your eggshells, then bake them in the oven at 100°C for 10-15 minutes. Once they’re cool, grind them into a fine powder using a coffee grinder or mortar and pestle. Sprinkle the powder around the base of your plants or mix it into your soil.
Banana Peel Tea:
Banana peels are rich in potassium and can help prevent potassium deficiencies in your plants. To make banana peel tea, simply soak a few cut up banana peels in water for 24-48 hours, then strain it and apply the mix to your plants as a foliar spray or soil drench.
Epsom Salt:
Epsom salt is an excellent source of magnesium and can help prevent magnesium deficiencies in your plants. To use Epsom salt, simply dissolve 1 teaspoon per liter of water and apply to your plants as a foliar spray or soil drench.
Wood ash:
A Wood ash tea can be a great source of potassium, phosphorus, calcium, magnesium and more trace elements if used correctly. To make wood ash tea, simply hang a small meshed bag of braai ashes and burnt wood in aerated water for 24-48 hours, then strain and mix with fresh water in a 1:20 ratio and apply to your plants as a foliar spray or soil drench. Beware of its liming effect which may raise the PH of your soil
Pro Tips and Best Practices for Healthy Cannabis Plants
In addition to understanding nutrient needs and deficiencies, there are several pro tips and best practices that you can implement to maximize the health and yield of your plants. Here are a few of our favorites:
Use Silica for Stronger Stems and Branches:
Silica is a vital nutrient that helps strengthen plant cell walls, leading to thicker, sturdier stems and branches. This can be especially beneficial for cannabis plants, which can become top-heavy during the flowering stage.
Incorporate Living Organisms for Healthier Soil:
 Living organisms such as earthworms, beneficial bacteria, and mycorrhizal fungi can help improve soil structure, increase nutrient availability, and boost overall plant health. To incorporate living organisms into your soil, try the following:
- Add earthworms to your soil mix to improve aeration and drainage
- Use a compost tea or microbial inoculant to introduce beneficial bacteria and fungi.
Practice Proper Pruning and Training Techniques:
Proper pruning and training techniques can help maximize yield, improve plant structure, and prevent pest and disease issues.
Monitor and Adjust Environmental Factors:
Environmental factors such as temperature, humidity, and light intensity can have a significant impact on plant health and growth. Use a thermometer or hygrometer to monitor temperature and humidity levels and adjust your ventilation and air circulation as needed to maintain proper airflow.
Use Cover Crops and Companion Planting:
Cover crops and companion planting can help improve soil health, prevent nutrient depletion, and deter pests and diseases.
Conclusion
That was a lot of information to take in. But don’t worry if you’re feeling a bit overwhelmed. The key takeaway here is that nutrient deficiencies are a fairly common issue that all cannabis growers face at some point. The important thing is to be proactive, pay attention to your plants, and investigate any issues as soon as you notice them.
Remember, growing weed is a learning process. Don’t be afraid to experiment, make mistakes, and ask for help when you need it. With a little bit of patience and perseverance, you’ll be well on your way to growing some top-quality bud.
If you’re looking for an easy way to get started with home growing in South Africa, be sure to check out our selection of autoflower grow kits and cannabis seeds at Seed and Soil SA. We’ve got everything you need to get started, including high-quality genetics, nutrient-rich soil, and step-by-step instructions.
Thanks for reading, and happy growing! And remember, if you have any questions or concerns about nutrient deficiencies or any other aspect of growing cannabis, don’t hesitate to reach out to us at Seed and Soil SA. We’re always here to help our fellow South African growers achieve their best harvests yet!
Here is a quick video guide of nutrient deficiencies in cannabis plants
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