Is it common for marijuana plants?
Potassium (K) deficiency occurs occasionally in both planting mediums and outdoors in soil, but rarely in hydroponics. Marijuana plants often suffer from mild potassium deficiencies, even in rich, well-fertilized soil, usually caused by improper fertilization. Many organic fertilizers such as guano, fish emulsion, alfalfa, cottonseed and blood meals, and many animal manures contain minor amounts of potassium relative to nitrogen and phosphorous.
Marijuana plants suffering from minor deficiencies look vigorous, even taller than the rest of the population, but the tips and edges of their bottom leaves die or turn tan/brown and develop necrotic spots.
As the deficiency gets more severe the cannabis leaves develop chlorotic spots. Mottled patches of red and yellow appear between the veins, which remain green, accompanied by red stems and petioles. More severe deficiencies result in slower growth, especially when thre marijuana plants are in the vegetative stage. Severe potassium shortages cause cannabis leaves to grow smaller than usual.
Larger fan leaves have some dead patches, or necrosis, on their margins. These leaves eventually turn brown and die off. Marijuana plants with potassium deficiencies tend to be the tallest.
Excess potassium causes fan leaves to show a light to dark yellow or white color between the veins.
Potassium is mobile.
Role in marijuana plant nutrition
Potassium is found in the whole marijuana plant. It is necessary for all activities having to do with water transportation, as well as all stages of growth; it’s especially important in the development of buds. K aids in creating sturdy and thick stems, disease resistance, water respiration, and photosynthesis.
Although symptoms of minor potassium deficiency affect the cosmetic look of the plant, it does not seem to affect marijuana plant growth or yields.
Water-soluble fertilizers containing high potassium fix the deficiency. Bloom fertilizer usually contains high potassium levels. It is used in the formulas to balance the pH. Highly alkaline potassium is used to balance acidic P. Wood ashes deliver K quickly.
Liquefied kelp, bloom fertilizers and wood ash are commonly used and work quickly to correct K deficiencies. So do potassium bicarbonate (KHCO3), potassium sulfate (K2SO4) and potassium dihydrogen phosphate (KH2PO4) Potassium silicate (K2SiO3) can be used to supply Si and has 3% K in it. Granite dust and greensand take more time to get to the plant and are not usually used to correct deficiencies, but to prevent them.
Damaged cannabis leaves never recover, but the plant shows recovery in four to five days with applications of fast-acting products.
Cold weather slows K absorption, as does too much Ca or NH4+. High levels of Na displace K.