There are many factors that can affect the way Cannabis plants use nutrients, so in this article we cover the causes of excess nutrient solution, how to identify the symptoms, causes and provide remedies.
Cannabis plants require three primary nutrients which are Nitrogen (N), Potassium (K) and Phosphorus (P). Next are trace elements which are Sulfur (S), Boron (B), Calcium (Ca), Copper (Cu), Iron (Fe) Magnesium (Mg), Manganese (Mg), Molybdenum (Mb) and Zinc (Zn). Even though plants are dependent on these nutrients during their lifecycle, sometimes it can happen that problems may arise in the garden.
There are several potential symptoms that will reveal signs of toxicity. As salts build up around the roots and in the growing medium, over time Cannabis plants may struggle to keep a well-balanced diet.
An overzealous beginner grower who does not measure their E.C or check their pH may notice their plants have become distressed, stunted, drooping and flower production may drastically halt. Of course there are other signs to be vigilant of such as discoloration, yellowing veins, brown spots and bronzing.
Nitrogen Toxicity: This is easily done when using chemical-based powder or liquid fertilizers. Cannabis plants will become dark green and the fan leaves will claw downwards. Too much Nitrogen during flowering will seriously inhibit bud and resin production and can also prevent clones rooting.
Phosphorus Toxicity: Most commonly occurring during flowering and especially with high amounts of bat guano, leaves will develop yellow veins appearance and the tips will have a white or burnt appearance. The leaves will also curl and reveal spots similar to a Cal Mag deficiency.
Potassium Toxicity: Too much Potassium can cause the leaves to lose vigor and become thin with brown rusty spots appearing and the outer parts of the leaves curling slightly and browning. Another nutrient that can significantly affect flower and resin production.
Understanding the differences between a deficiency and an excessive amount of nutrients can be difficult. Even old school growers, who have a good 30 years experience under their belts, may not always know what chain of events has caused which deficiency or toxicity symptom. Once you can identify the signs of too much N, P and K, then using the principles of detection and the list below, you can soon figure out what the issue is.
Calcium: Too much Calcium will cause an imbalance with other trace elements, and is easily recognizable as it causes tip burn.
Sulfur: Feeding excessive amounts of Sulfur during the flowering period can cause stunted growth, and slow flower production down. Foliage will turn dark green and cause plants to droop slightly and lose vigor.
Boron: This toxicity will begin with a slight browning of the outer parts of the healthy foliage, and over time turn half of the leaf yellow with veins.
Magnesium: As Calcium and Magnesium are so closely related, the signs of excessive Magnesium will be brown spots, with some parts of the leaf turning rusty brown and falling off. O.G Kush cultivars are particularly Magnesium heavy during their life cycle.
Copper: The leaves will begin to turn yellow with some curling. The leaf color will be similar to pale lime.
Iron: Symptoms of too much iron will cause new green growth to begin yellowing, and slowly bronze. Late stages of Iron toxicity will be pale yellow leaves, with dark green veins on the surface.
Manganese: The edges of the leaves will become white and cause the coloration to shift. This will also cause brown spots to appear on the surface, similar to a Magnesium deficiency.
Molybdenum: Maybe the easiest symptom to identify, as the leaves will turn from a healthy green, to a mix of purple and light orange. Typically seen during the flushing stage when Cannabis plants are only fed plain water.
The events that lead up to a Cannabis plant showing signs of malnutrition or deficiencies, and that of excessive toxicity, can be extremely diverse. Knowing what has caused the plant to display one or the other is one part of the equation, but knowing how to solve the issue quickly is the other. A common mistake that can be easily made, especially if working with hydroponic chemical nutrients, so below is a list of symptoms associated with nutrient deficiency.
Nitrogen: Older green and healthy foliage will become pale yellow and lifeless. New foliage will use the Nitrogen from the older and bigger leaves when this happens.
Phosphorus: The leaves will become light green and brown spots will appear. The leaves will feel stiff and thick compared to before.
Potassium: Outer parts of the leaves will become lighter and turn dark brown. Over time, the leave will curl up and become lifeless.
Calcium: Brown spots will appear on the leaf that have a rusty appearance. If not treated in time, the leaves will take on a pale yellow color.
Sulfur: New foliage may appear bright green with signs of veins appearing throughout the leaf. The lower will turn yellow first, so do not confuse the early signs with Nitrogen deficiency.
Boron: Late symptoms of a Boron deficiency will be multicolored leaves appearing. The outer parts of the leaf may have an orange or brown tint.
Magnesium: Cannabis plants that are heavy users of Magnesium, such as O.G Kush, will find that leaves will lose the vibrant green and will have patches of yellow and brown spots appearing.
Manganese: Brown spots will appear over pale colored leaves. Similar to a Cal Mag deficiency.
Iron: The center part of the leaf will begin to yellow and later on, can cause the whole leaf to lose its green color, revealing green veins on the leaf surface.
Copper: The tips and edges of the leaves will turn yellow and look similar to tip burn.
Molybdenum: Red and pink coloring will appear and is typically seen when plants are being flushed of all nutrients.
Too much salt builds up will only cause more problems over time. Flush your growing medium with only water and try to get the plants back to a healthy and happy state before feeding with nutrients again,
Always check your nutrient solution by using a digital E.C pen. This allows you to have an exact decimal reading of your solution.
The pH of your water source is also essential for the availability of an organic or hydroponic garden. Hydroponics require a pH of 5.5-6.0 and drifting should be carefully monitored.