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How To Prevent And Fix Every Cannabis Nutrient Deficiency

How To Prevent And Fix Every Cannabis Nutrient Deficiency

By Luke Sumpter

Nutrient deficiencies: How to prevent and fix them.

Contents:

  1. Macro vs micronutrients
  2. Mobile vs immobile nutrients
  3. Ph matters
  4. Going organic
  5. How to prevent and solve nutrient deficiencies
    1. Nitrogen
    2. Phosphorus
    3. Potassium
    4. Calcium
    5. Sulphur
    6. Magnesium
    7. Iron
    8. Manganese
    9. Boron
    10. Molybdenum
    11. Zinc

Just like us, cannabis plants require a varied and healthy diet to survive and thrive. They need the right amount of nutrients to fulfil important physiological functions, and if they lack just one piece of the puzzle, growth will slow down and yields may be affected.

Luckily, the cannabis plant does a pretty good job of communicating what it needs. If nutrient deficiency strikes, it often sends out a signal—wilting, discolouration, curled leaves—to inform the cultivator of what it requires.

Before we dive into how to prevent and fix each nutrient deficiency, they are a few important things you should know.

Video id: 266470214

MACRO VS MICRONUTRIENTS

Macronutrients are minerals that cannabis plants require in large amounts. These include nitrogen, phosphorus, and potassium. Just like fats, carbs, and protein form the cornerstone of the human diet, cannabis needs these important minerals in large quantities to carry out key processes.

Micronutrients are minerals and elements required in much smaller amounts. However, they are just as vital to plant health. These include iron, zinc, sulphur, boron, and others. Think of them like minerals and vitamins in the human diet. We don’t need much of them, but without them, it wouldn’t take long to autumn ill.

MOBILE VS IMMOBILE NUTRIENTS

Learning the difference between mobile and immobile nutrients can help growers diagnose deficiencies more accurately.

Mobile nutrients are minerals that can be shuttled throughout the plant to areas that need them the most. For example, phosphorus stored in older fan leaves can be directed towards newer growth if a deficiency occurs. Therefore, deficiency of a mobile nutrient will first become noticeable in older growth.

Immobile nutrients remain locked in place and plants cannot redistribute them. For example, if a zinc deficiency takes hold, the signs will first show in the newer growth as the plant can’t relocate its mineral stash.

MOBILE VS IMMOBILE NUTRIENTS
ELEMENTS (Symbols) MOBILITY IN PLANT NUTRIENT DEFICIENCY
FOUND IN
Nitrogen
(N)		 Mobile Old leaves
Phosphorous
(P)		 Mobile Old leaves
Potassium
(K)		 Mobile Old leaves
Calcium
(Ca)		 Immobile New leaves
Sulfur
(S)		 Immobile New leaves
Magnesium
(Mg)		 Mobile Old leaves
Iron
(Fe)		 Immobile New leaves
Manganese
(Mn)		 Immobile New leaves
Boron
(B)		 Immobile New leaves
Molybdenum
(Mo)		 Immobile New leaves
Zinc
(Zn)		 Immobile New leaves

PH MATTERS

Your soil can hold all of the nutrients your plant needs, but it won’t be able to access them if the pH is off. Cannabis plants thrive in a soil pH of between 6.0–6.5. Any lower or higher and plant roots will struggle to absorb key nutrients—a phenomenon known as nutrient lockout. Routine flushes can prevent this from happening. Keep an eye on your values using a pH meter. You can also change the pH of your soil using these techniques.

GOING ORGANIC

Advances in soil science have shown that the rhizosphere (root zone) is beaming with life. Here, a complex network of microorganisms works synergistically with the root system. The soil needs an optimal balance of bacteria and fungi to break down organic matter and free up nutrients for plants to use.

Focusing on composting and building living soil provides long-term prevention of nutrient deficiencies and supports thriving biodiversity within the rhizosphere. Such beneficial life will help your yields soar.

However, growers can take more direct action in the short-term. Foliar spraying can be administered as a quick fix when plants are missing out on some nutrients. These feeds bypass the roots and are absorbed straight through the leaves.

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HOW TO PREVENT AND SOLVE NUTRIENT DEFICIENCIES

Below is a list of key nutrient deficiencies that may arise, as well as how to prevent them and fix them if they strike.

NITROGEN

A mobile macronutrient, nitrogen plays a major role in photosynthesis and the formation of vital plant proteins. Nitrogen deficiency can result in yellowing older leaves, older leaves dropping off, eventual discolouration of the entire plant, and reduced yields.

Image of a cannabis plant showing signs of nitrogen deficiency, characterized by yellowing older leaves and overall discolouration. The visual serves as an example in a plant deficiencies chart, highlighting the importance of nitrogen in photosynthesis and plant health.
How to prevent
  • Keep pH within an optimal range (6.0–6.5).
  • Start off with a nutrient-dense potting mix.
  • Start composting to ensure a nutrient-dense medium in the future.
  • Mycorrhizae are associated with nitrogen-fixing bacteria. Add them to your soil to boost nitrogen levels.
How to fix
  • The majority of organic fertilisers contain enough nitrogen to fix the deficiency: Try fish meal, manure, alfalfa, or feather meal.
  • Adjust pH accordingly.
  • Apply compost tea as a foliar spray for a fast-acting solution.
  • Increase the amount of nitrogen in your compost using kitchen scraps, fresh prunings, and grass clippings.

PHOSPHORUS

Phosphorus also acts as a macronutrient in the cannabis plant. Being a mobile nutrient, plants can direct the mineral to the areas that need it most. Phosphorus plays an essential role in photosynthesis and protein synthesis, and it's a crucial component of DNA. Phosphorus deficiency can manifest as red/purple stems, brown spots on leaves, and dry leaves.

Image of a cannabis plant exhibiting signs of phosphorus deficiency, including red/purple stems and brown spots on the leaves. This visual is part of a plant deficiencies chart, emphasizing the importance of phosphorus for photosynthesis, protein synthesis, and overall plant health.
How to prevent
  • Utilise soil high in organic matter.
  • Increase the absorption rate by using well-aerated soil.
  • Use mycorrhizal fungi in your soil to improve phosphorus uptake. These microbes help to turn insoluble phosphates into available molecules.
  • Add more manure to your compost.
How to fix
  • Nudge pH up to the higher end of the spectrum—your plant will have an easier time absorbing it.
  • Add worm castings and fish meal to your soil.
  • Apply an organic fertiliser high in phosphate.
  • You may be overwatering. Only water when the top 3cm of soil is dry to avoid making the medium overly compact.
  • Move your plants to a warmer location or erect a tarp to trap heat. Plants find it harder to uptake phosphorus in temperatures below 15°C.

POTASSIUM

Potassium: the third and final macronutrient. It helps to regulate CO₂ uptake and plays a role in photosynthesis. The mobile nutrient also helps in the production of ATP (the cellular unit of energy). Potassium deficiency appears as brown and yellow leaf tips and edges, curled-up leaves, and stretching.

Image of a cannabis plant showing signs of potassium deficiency, characterized by brown and yellow leaf tips, curled-up leaves, and stretching. This visual is part of a plant deficiencies chart, highlighting the importance of potassium in regulating CO₂ uptake and photosynthesis.
How to prevent
  • Be careful when using fertilisers. Feeding your plant too often can cause salt to build up and interrupt potassium uptake.
  • Bolster your compost with hardwood ash and kelp meal.
  • Don’t overwater.
How to fix
  • Flush the medium.
  • Measure and adjust pH to correct possible nutrient lockout.
  • Add chicken manure to the soil.
  • Apply organic seaweed as a foliar spray.

CALCIUM

Critical to plant health, this immobile micronutrient helps to hold plant cell walls together. Calcium deficiency can lead to new growth—root tips and young leaves—forming incorrectly and becoming warped.

Image of a cannabis plant displaying symptoms of calcium deficiency, with distorted new growth at the root tips and young leaves. This visual is part of a plant deficiencies chart, emphasizing the role of calcium as a critical micronutrient for maintaining plant cell structure.
How to prevent
  • Add dolomitic lime/garden lime to the growing medium.
  • A pH of 6.2 provides the best environment for calcium uptake.
  • Add plenty of eggshells to your organic compost.
  • Keep a worm farm! Worm castings provide loads of nutrients, including calcium.
How to fix
  • Apply a cal-mag supplement.
  • Increase or decrease pH towards 6.2.
  • Add one teaspoon of hydrated lime to 4l of water and use the solution to water your plants.

SULPHUR

Although required in very small amounts, this key immobile nutrient contributes to forming vital enzymes and proteins. A sulphur deficiency will lead to yellowing of new growth and discolouration on the undersides of leaves.

A visual representation of sulfur deficiency in cannabis plants, showing yellowing of new growth and discoloration on the undersides of leaves. The image is part of a plant deficiencies chart that highlights key nutrient deficiencies and their effects on plant health.
How to prevent
  • Bolster your compost pile with manure.
  • Fungi and bacteria are key for releasing sulfur in the soil. Employ techniques such as no-till to encourage them and add some mycorrhizae if you’re growing in pots.
How to fix
  • Epsom salts are rich in sulphur. Add 1–2 teaspoons of Epsom salts to about 4l of water and supplement until symptoms disappear.
  • Adjust pH to the optimal range if needed.

MAGNESIUM

Without this mobile micronutrient, photosynthesis would not be possible. The mineral sits at the heart of the chlorophyll molecule and enables it to absorb light. Magnesium deficiency will result in lower growth looking worse for wear. Leaves will become yellow, dry out, and eventually turn brown.

An illustration of magnesium deficiency in cannabis plants, displaying yellowing leaves that eventually dry out and turn brown. This image is part of a plant deficiencies chart that outlines the importance of magnesium for photosynthesis and overall plant health.
How to prevent
  • Include dolomitic limestone in the growing medium.
  • Use compost rich in manure.
  • Maintain good pH balance.
How to fix
  • Flush the medium with 6.0 pH water if pH is out of balance.
  • Epsom salts also provide magnesium. Add 1–2 teaspoons of Epsom salts to about 4l of water and apply until symptoms resolve.

IRON

Iron plays an essential role in chlorophyll formation. The element also forms part of several enzymes and some important pigments. Overall, this immobile micronutrient helps plants carry out metabolic and energy-forming processes. If your plant experiences iron deficiency, you’ll notice young growth at the top of the plant becoming bright yellow.

An illustration of iron deficiency in cannabis plants, showing bright yellowing in the young growth at the top. This image is part of a plant deficiencies chart highlighting the importance of iron for chlorophyll formation and overall plant metabolism.
How to prevent
  • Help your plants absorb existing iron by adding mycorrhizae to the soil. These synergistic organisms help to shuttle the element into the root system and beyond.
  • Test your soil pH to rule out nutrient lockout.
  • Add chicken manure, kitchen scraps, and seaweed to your compost pile.
How to fix
  • Hit the pH sweet spot.
  • Flush the growing medium and add an iron supplement afterwards.
  • Use a small amount of nitrogen fertiliser to lower pH and make iron more accessible.

MANGANESE

Manganese doesn’t receive too much attention in the world of cannabis growing. However, this immobile micronutrient plays a fundamental role in cannabis physiology. It aids photosynthesis, respiration, nitrogen assimilation, and root cell elongation, and protects roots from bad microbes.
Manganese deficiency will show up as light green discolouration near the base of new growth. This eventually spans out to the tips, and brown spots begin to emerge.

An illustration depicting manganese deficiency in cannabis plants, showing light green discoloration near the base of new growth that spreads to the tips, along with emerging brown spots. This image is part of a plant deficiencies chart emphasizing the essential role of manganese in cannabis physiology.
How to prevent
  • Imbalanced pH often underpins manganese deficiency. Frequently measure your soil pH and keep it within the optimal range to ensure your plants can access this mineral.
  • Make a manganese-rich compost by adding pineapple, tomatoes, cranberries, and carrots to your pile.
How to fix
  • Flush your containers.
  • Prune back any affected growth that doesn’t recover.
  • Hit the canopy with a seaweed foliar spray.

BORON

Boron works alongside calcium to give integrity to plant cell walls and help with cell division. Breeders also have a soft spot for this immobile nutrient as it helps with the pollination process. A lack of boron will lead to deficiency symptoms such as a lack of turgor, reduced fertility, poor vegetative growth, and terminated meristems. New growth will become twisted, sugar leaves will wilt, and leaves will show a yellowish-brown discolouration.

An illustration showing boron deficiency in cannabis plants, highlighting twisted new growth, wilting sugar leaves, and yellowish-brown discoloration. This image is part of a plant deficiencies chart, emphasizing boron's role in maintaining plant integrity and supporting the pollination process.
How to prevent
  • Don’t let plants dry out often.
  • Avoid nutrient lockout by NOT overfeeding.
  • Don’t let humidity levels drop below 25%.
  • Use well-draining, aerated soil.
  • Add generous amounts of apples, bananas, broccoli, and chickpeas to your compost pile.
How to fix
  • Flush the medium and aim for an ideal pH range.
  • Mix one teaspoon of boric acid in 4l of water and apply to affected plants.

MOLYBDENUM

Another lesser-known nutrient, molybdenum helps to form two essential enzymes that convert nitrate into nitrite and then into ammonia. Plants use the latter to make amino acids, which eventually become proteins. If your plants become deficient in molybdenum, they’ll start to display red and pink discolouration at the edges of new growth. Leaves will also start to become yellow and spotted. Thankfully, molybdenum deficiency is quite rare.

An illustration depicting molybdenum deficiency in cannabis plants, showing red and pink discoloration at the edges of new growth, along with yellowing and spotted leaves. This image is part of a plant deficiencies chart, highlighting the role of molybdenum in enzyme formation for amino acid production.
How to prevent
  • Keep pH between 6.0–6.5.
  • Start your grow with good-quality, living compost.
  • Throw the occasional bean, pea, grain, and raw nut onto your compost.
How to fix
  • Flush and adjust pH.
  • Spray affected plants with a seaweed foliar spray.
  • Water plants with a worm casting compost tea.

ZINC

Plants don’t need much zinc at all, but illness will strike if they miss out. Zinc forms parts of proteins, membranes, and growth hormones. The immobile micronutrient also regulates enzyme function and stabilises DNA and RNA. What happens when zinc goes missing? Deficiency symptoms manifest in slowed new growth; the distance between nodes lessens, and leaves will look wrinkly and yellow. Eventually, new leaves will display yellowing and rust-coloured tips.

An illustration showing zinc deficiency in cannabis plants, characterized by slowed new growth, reduced distance between nodes, and wrinkly yellow leaves with yellowing and rust-colored tips. This image is part of a plant deficiencies chart, emphasizing the importance of zinc in protein formation, enzyme regulation, and plant growth.
How to prevent
  • An excessively alkaline pH causes most zinc deficiencies. Maintain proper pH.
  • Boost zinc levels in your compost using pumpkin and squash scraps.
  • Good microbes play a large role in zinc uptake—add beneficial fungi to your growing medium
How to fix
  • Reduce alkaline pH to the ideal range.
  • Stop overwatering.
  • Use a fish or seaweed foliar spray to swiftly boost zinc levels.
Cannabis nutrient deficiencies
 
Cannabis nutrient deficiencies
 
 
Cannabis nutrient deficiencies
 
 
 

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