There are many common deficiencies that can occur when growing cannabis plants. As a new grower, it can be tricky trying to figure out exactly what deficiency your plant is experiencing. I’m here to help. I will be discussing the 6 most common deficiencies in cannabis plants, how to identify them and ways to correct the deficiency.
Check Your pH First
Many leaf symptoms that occur are caused by an incorrect pH. If the pH is off, it can cause a deficiency simply due to not being in the correct range for absorption for that particular nutrient. So, always remember to check your pH first. If it is an issue of pH, you can simply adjust the pH and it will fix the problem.
If you’re sure that your pH is in the ideal range. Then, it could have been one of the following common deficiencies in cannabis plants.
Nitrogen is a micronutrient that plays an important role in photosynthesis and the production of chlorophyll. It is a mobile nutrient which means the older growth will show symptoms first. Nitrogen deficiency will cause yellowing of lower leaves that will eventually wilt and die. The entite plant will be more pale or lime green looking as well. Once it progresses, the yellowing will move up the plant to newer growth. It can cause the plant to go into flower early and produce less yields.
You can correct a nitrogen deficiency, you can make a compost tea to deliver the nutrients quickly. You can use ingredients high in nitrogen such as worm castings, blood meal, feather meal, or bat guano. Simply put your ingredients into a cheesecloth teabag and put the teabag into a 5 gallon bucket. Add a pump with air stone to the bucket and add your water. Let the pump oxygenate the water for at least 24 hours and up to 48 hours. Then, simply use this water to water plants.
You can also make a quick and simple nitrogen boost by boiling 1 black tea bag and about 1 tbsp of oatmeal in a 32oz mason jar. Let it cool and sit for at least an hour, but the longer the better. Water your plants with this water for a boost of nitrogen.
For an easy DIY Nitrogen Rich liquid fertilizer, check out the link. This recipe uses weeds from outside or grass clippings. This is best done during the warmer months when grass and weeds are readily available.
Phosphorus is an important macronutrient for photosynthesis and proper root development. Phosphorus is a mobile nutrient which means it will show symptoms in the lower growth first. It can be disastrous for the seedling or young plant. In mature plants, it can cause stunted growth, low yields, delayed flower and reduced resin production. Early signs include purpling of lower stems, followed by the lower leaves turning a shade of dark blue-green. If it progresses, the leaves will develop brown, bronze, copper or blackish-purple spots. The leave will curl up and eventually fall off due to the dead spots.
To correct a phosphorus deficiency, you can make a compost tea using ingredients such as mineralized or rock phosphate, bone meal, or fishbone meal.
You can also use Banana Peel Tea for a mild case as it contains phosphorus as well.
Potassium is vital to plant growth and without it, plants wouldn’t grow. It’s important to water intake, root growth, cell division and production, and movement of carbohydrates/sugars. It also helps make the plant more resistant to pests and diseases. Early signs include bronze or brown burnt edges and tips on the leaves (especially on older growth). It can look like nutrient burn, except there is yellowing on the margins of the burnt edges/tips. If it progresses, it will cause leaf burn, dehydration and new growth will curl. Phosphorus deficiency will cause severely decreased yields, weak growth and susceptibility to pests and diseases.
An easy fix for a potassium deficiency is Banana Peel Tea which is high in potassium. You can also make a compost tea with ingredients like seaweed extract or kelp meal.
Calcium is crucial for cell integrity and growth. It also helps with the flow of nitrogen and sugars throughout the plant. First symptom is curling and distortion of lower leaves. This is followed by yellow-brownish or brown spots with brown borders that grow over time. Finally, it will cause root tips to wither and die, which causes stunted plants with low yields.
Magnesium is used in high volume during photosynthesis because magnesium is the central atom in the chlorophyll molecule. It is vital for absorption of energy from the light. Magnesium also aids enzymes in creating carbohydrates/sugars that produce flowers. Signs of a deficiency will not show until 3 to 6 weeks after it has started. It can quickly progress in flower and cause low yields. It will cause the areas between the veins to yellow on lower leaves. As it continues, it will move up the plant and the yellowing will increase and effect the margins and tips as well. The plant will look unhealthy, droopy and some leaves will curl, die and fall off.
For a calcium and/or magnesium deficiency, you can make a DIY Calcium Phosphate for creating DIY CalMag+. You can also make a simple CalMag solution by adding 5-6 dry egg shells and 1 tbsp plain epsom salt to a gallon pot and add water. Boil the water until the epsom salt dissolves and then let cool and soak for 24 hrs before using on your plants. Use 2 cups of the solution to water each plant. This recipe makes 8 treatments.
If you’d like to learn more about each nutrient and their deficiencies, check out my article on mobile & immobile nutrients.
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