Problem: The initial symptoms may appear similar to a nitrogen deficiency (yellowing of older, lower leaves). Leaves may become mottled or spotted. However, the tell-tale sign of a molybdenum deficiency is the leaves may start to display a unique orange, red or pink color around the edges which will start to move toward the center of the leaf. Sometimes the color appears in the middle of the leaves as opposed to the edges.
A real molybdenum deficiency in cannabis is rare, and even scientists did not realize this mineral is needed by most plants because it is often present in low concentrations all the time.
For cannabis plants, molybdenum tends gets locked out at lower pH ranges. Your cannabis plant may show signs of a molybdenum deficiency if the pH at the roots is too low, although it is likely that molybdenum is there. That is because when the pH of your root zone is off, your cannabis cannot properly absorb molybdenum through its roots. Therefore the first step is to ensure that you have the correct pH for your growth medium.
Please note: After a molyndenum deficiency is cleared up, the problem (pink coloring and yellowing leaves) will stop appearing on other parts of the plant, usually within a week. Please note that leaves which have been damaged by a molybdenum deficiency will probably not recover or turn green, so you want to pay attention to other growth for signs of recovery.
- 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
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 remove any nutrient salts that may be preventing the uptake of molybdenum and help restore pH to the proper levels..