Nutrients are classified as either immobile or mobile depending on if it can be moved around the plant once it’s been fully absorbed. Mobile nutrients are stored in older leaves and can be moved around the plant wherever it’s needed. Immobile nutrients stay close to where they were originally deposited.
Deficiencies & excess of mobile nutrients will appear in older growth and leaves first. Where as, deficiencies & excess of immobile nutrients will appear in new growth first usually at the top of the plant. Once you understand the difference and which nutrients are mobile and immobile, it makes it easier to diagnose & fix deficiencies.
Whenever you suspect a deficiency, always check your pH first and ensure that it is in the correct range. If it isn’t within the correct range, it won’t be able to absorb some nutrients. So, you could be treating a deficiency, but if the pH is off, it won’t be able to absorb the nutrient still. If your pH is in the correct range, you can now try to figure out what’s going on.
Primary Nutrients
Nitrogen – Mobile
The most common deficiency for cannabis plants. It is vital for photosynthesis and production of chlorophyll. Even though nitrogen is readily available in the atmosphere, most plants cannot intake the nitrogen from the air. Rather, it needs to take it in from the soil via its roots.
Early signs of deficiency is a lightening of the entire plant and severe yellowing on lower growth. Once it progresses, the yellowing will move up the plant to newer growth and leaves will curl and fall off. Brown spots and discoloration are also possible. The plant will have less bud sites and go into flower early.
Phosphorus – Mobile
A phosphorus deficiency is not common and usually happens due to the pH going above 7.0. Phosphorus is vital for proper root development & photosynthesis. If the is a deficiency early on, it can be devastating to the seedling or young plant. In mature plants, it can cause stunted growth, low yields, delayed flower and poor resin production.
Early signs of deficiency are purpling of older leaf stems followed by leaves turning a shade of dark blue-green. As it progresses, plant growth slows down dramatically and blackish-purple or dark copper spots appear on leaves. Leaves can turn a metallic purple or dark bronze in colour. Dead spots will start to form on leaf stems while leaves curl up and fall off.
Potassium – Mobile
Without it, plants would not grow. It is important for so many plant processes such as water intake, root growth, cell division & production and movement of carbohydrates/sugars. Potassium also helps to strengthen the plant immune system, making it more resistant to pests and diseases.
Early signs of deficiency include dull, overly green leaves followed by “burnt” rusty brown leaf tips, general yellowing, and brown spots especially on older growth. It will progress to leaf burn, dehydration and curling of newer growth. If not corrected, plants will have weak growth, drastically reduced flowers, and be very susceptible to pests and diseases.
Secondary Nutrients
Magnesium – Mobile
It is used in very high numbers as it is the central atom in the chlorophyll molecule. It is critical in the absorption of energy from light. Magnesium also aids enzymes in creating carbohydrates and sugars that produces flowers.
The signs of deficiency will not show until after 3 to 6 weeks after the deficiency started. It can quickly escalate during flower and cause low yields. It will cause the areas between the veins in older leaves to yellow. Rust coloured spots will also form. As it progresses, the yellowing will move up the plant and the spots will increase in number and size and affect the margins and tips of the leaves. The plant will look droopy and unhealthy and some leaves will curl, die and drop.
Calcium – Immobile
It is crucial for cell integrity and growth. Calcium helps with the flow of nitrogen and sugars throughout the plant. Deficiency usually happens with hydroponics or outdoors in very wet, cool conditions with acidic soil. First sign is distortion and curling of lower leaves. This is followed by irregular yellow-brownish spots with brown borders that grow over time. Finally, root tips will wither and die resulting in a stunted plant with low yields.
Sulfur – Immobile
It is important for production of oils and terpenes. Sulfur is crucial for plant respiration and the synthesis and breakdown of fatty acids. It’s an uncommon deficiency for cannabis plants and is usually a result of loss of phosphorus due to high pH levels (above 7.0) in the root zone. Early signs include young leaves turning lime green then yellow with stunted growth. As it progresses, leaf veins will yellow and the leaves become dry and brittle. If the deficiency continues, it will result in slow, weak flower production with low potency.
Micronutrients
Copper – Immobile
It is needed only in trace amounts and a deficiency is very rare. Copper aids on nitrogen fixation, carbohydrate metabolism, and oxygen reduction. Early sign of deficiency is the slow wilting, twisting and turning of new growth. Dead spots will form on leaf tips and margins and the entire plant could wilt.
Iron – Immobile
It is essential for nitrate and sulfate reduction and assimilation. Iron is also a catalyst for the production of chlorophyll. Deficiencies are usually due to excessive amounts of copper, manganese or zinc or improper pH. Early sign of deficiency is yellowing between the veins of the leaves in the base of new leaves. As it progresses, the interveinal yellowing will spread to older leaves as well.
Manganese – Immobile
A deficiency is rare and usually caused by high pH or an excess in iron. Manganese helps the plant to use nitrogen and iron for chlorophyll production as well as aiding in oxygen reduction. Early sign of deficiency is yellowing between leaf veins in new growth. This is followed by necrotic or dead spots on leaves. As it progresses, it will gradually spread to older growth. The most obvious sign is when the leaf veins and margins remain green around the yellowing of interveinal areas.
Zinc – Immobile
Zinc is vital for sugar and protein production. It also helps with the formation and retention of chlorophyll for healthy stem growth. Deficiency is common especially in alkaline soil and dry conditions. It is usually a result of high pH. Early signs include young leaves and new growth having interveinal yellowing, with small thin leaf fingers that wrinkle and distort. Then, discoloured and burnt leaf tips followed by leaf margins and finally brown spots. The most obvious sign is leaves that turn at a 90° angle.
Boron – Immobile
This element helps with the absorption of calcium. A boron deficiency is pretty rare unless a plant is under-watered or in very dry conditions. It is usually accompanied by other pH or nutrient issues that affect the leaves. Early signs include abnormal or thick growth tips along with brown or yellow spots on new growth. New growth may be twisted, wrinkled or curl and may die off. The interior of the roots may soften, making it more susceptible to diseases.
Cobalt – Immobile
It is necessary for efficient chemical and biological processes within the plant. It is important for nitrogen absorption. A cobalt deficiency will display similar symptoms to that of a nitrogen deficiency.
Chlorine/chloride – Immobile
Chlorine, in the form of chloride, is important for photosynthesis and cell division in roots and foliage. Early signs include new growth turn pale and roots grow stout. As it progresses, the leaves turn a characteristic tanned colour, develop thick tips and stop growing.
Silicon – Immobile
It is absorbed as silicic acid by cannabis plants and helps balance magnesium and iron levels. Deficiencies or excesses don’t cause complications.
