Your cannabis plant may show signs of a magnesium deficiency if the pH at the roots is
too low, especially in hydro. That is because when the pH of your root zone is not in the correct range, your cannabis cannot properly absorb magnesium through the roots.
Often with this deficiency, the magnesium is present, but the roots cannot absorb the magnesium properly due to an improper pH. Therefore it is very important to
maintain the correct pH (and make sure the pH does get to low / acidic) in order to avoid a magnesium deficiency.
Adding more magnesium to a system when there is a pH lock-out will probably not help because the plant will not be able to absorb any magnesium until the pH has been corrected.
Please note: Once a magneisum deficiency is cleared up, the problem (yellowing lower leaves) will stop spreading to other older leaves, usually within a few days. Please note that leaves which have been damaged by a magnesium deficiency will probably not recover or turn green, so you want to pay attention to other growth for signs of recovery.
- In soil, magnesium is best absorbed by the roots in the 6.0 - 7.0 pH range (some growers say a 6.5 - 7.0 pH is best if you suspect a magnesium deficiency)
- In hydro, magnesium is best absorbed by the roots in the 6.0 - 6.5 pH range (in hydro, it's generally recommended to keep the pH between 5.5 - 6.5, but magnesium specifically tends to be best absorbed above 6.0)
If you suspect your growing cannabis plant has a magnesium deficiency, flush your system with clean, pH'd water that contains a regular dose of
cannabis-friendly nutrients that includes magnesium. This will remove any nutrient salts that may be affected the uptake of magnesium and help restore pH to the proper levels..
To supplement with extra Magnesium...
Calcium,
magnesium, and iron deficiencies often appear together in cannabis. Many growers decide to purchase some sort of Calcium-Magnesium (often called
Cal-Mag) supplement for their grow room in case this common deficiency appears.
Listed below are common cannabis Calcium supplements, along below with some general information about each one. After supplementing with Cal-Mag and correcting the pH, you should expect to see new healthy growth within a week. Remember, the old leaves will probably not recover, but new growth should be green and healthy.
