Cannabis Iron Deficiency Iron deficiencies can occur on occasion in planting mediums, hydroponic systems, and in outdoor marijuana plants. In the event of an iron deficiency, you will notice a lack of chlorophyll in the new leaves, but they will not contain necrotic spots. These leaves will turn bright yellow with green veins. Newer leaves will exhibit "chlorotic molting" which produces brown marks on the leaf center. Iron Deficiency Can Look Similar to a Magnesium Deficiency Iron deficiencies are similar to magnesium deficiencies except that iron affects all new cannabis growth except the lower leaves. Magnesium affects the lower and middle leaves at the start. Iron does not move fast around the marijuana plant, giving it a low mobility. Iron is vital particularly for younger, still growing tissues in the marijuana plant. Enzymes require iron to function properly, and iron also allows for the synthesis of chlorophyll. How to Fix an Iron Deficiency in a Cannabis Plant Solving this issue isn't easy, but the right fertilizer and water balance can help. There are other options at your disposal. For instance, you can opt for a foliar feeding option with a chelated iron fertilizer that also contains zinc and manganese (iron, zinc, and manganese deficiencies often occur in conjunction. Other fast-acting options include: Iron chelates Iron oxides (Fe2O3 or FeO) Iron sulfate (FeSO4) These should be added filially and directly to the planting medium itself. Rusty water may also be a solution. An Fe deficiency may indicate a pH imbalance. Foliar feed with Fe chelated fertilizer containing Fe, Zn, and Mn, since these deficiencies are often found in combination. Other Fe-bearing supplements include compost, Fe chelates (often found in hydroponic micronutrient supplements), iron oxides (Fe2O3, FeO), and iron sulfate (FeSO4) for fast absorption. Supplements should be added both filially and to the planting medium. Adding rusty water also works.