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Molybdenum Deficiency

Molybdenum an essential micronutrient

Molybdenum is a micronutrient utilized by your plant to synthesize amino acids and is needed in very small quantities. Molybdenum also helps in nitrite/inorganic phosphorus conversion to usable forms to uptake. Toxicities and deficiencies in cannabis are rare with deficiencies being the more common of the two.

Deficiencies can be easily misconstrued as a nitrogen issue and since its relationship with nitrogen within your plant it even resembles one. with the plant’s oldest leaves yellowing. Leaves can be spotted with smears of blotches randomly and have orang, red or pink around the edges eventually moving inward. 

Correcting a Molybdenum Deficiency

Although this is a very uncommon occurrence, a molybdenum deficiency can be an issue for growers. As it is an integral part amino acid synthesis in plants and converting nitrates to nitrites that then turn into ammonia which can be use by your plant. It also has a role in the conversion of inorganic phosphorus into organic forms usable by your plant.

First things you will want to check are your nitrogen delivery and pH of your media and nutrient solutions. 

Molybdenum becomes less and less available under pH’s of 7 and while pH’s of 6-7 will be optimal for molybdenum absorption. As your media and solution approaches pH’s below 5.5, deficiencies will more common. 

  • In soil, molybdenum is best absorbed by the roots in the 6.0 – 7.0 pH range (some growers recommend avoiding a soil pH of lower than 6.5 if you suspect a molybdenum deficiency)
  • In hydro, molybdenum is best absorbed by the roots in the 5.5 – 6.5 pH range

Molybdenum’s role in converting nitrate a poison for plants into nitrate and then in to ammonia means fertilizers high in nitrates/nitrites will deplete your available levels of molybdenum in your soil/media. If you suspect your growing cannabis plant has a molybdenum deficiency, flush your system with clean, pH’d water that contains a regular dose of cannabis-friendly nutrients that includes molybdenum. This will hopefully correct any issues from fertilizers or pH and rebalance your media. 

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