After being asked the following question for the millionth time I decided it may be an issue that needed to be addressed.
Why if I am feeding my plant plenty of Magnesium does my plant show signs of Magnesium deficiency no matter what I do?
It is possible to be feeding an excess of most nutrients and still be deficient in one or more of them. This is because sometime plants can suffer from “Nutrient Antagonism.” Nutrient Antagonism is when an excess of a particular element BLOCKS the absorption of another element the plant needs. This can happen with elements of a similar size and charge (+ or -). Some of the most common antagonisms are:
• Iron blocking Manganese (or the reverse)
• Magnesium blocking Calcium (or the reverse)
• Potassium blocking both Magnesium & Calcium
Another reason for a plant being deficient in an element that is being applied in an appropriate dosage is called “BINDING.” Binding is when elements mix together and bond forming a compound that is insoluble (can not be absorbed by a plant’s roots.) This is seen when:
• Concentrated acids or bases are mixed into nutrient solution and a cloud of precipitate forms (the precipitate or milky cloud formed is actually elements “binding” and becoming unavailable to the plants.)
• Also when Iron or Zinc are mixed in a solution of Phosphates (HPO4-2) and a mineral called Strengite forms. This compound is completely insoluble and will make both the Phosphorous and the Iron or Zinc unavailable to plants.
A heavy flush with plain pH adjusted water followed by the application of fresh nutrient solution can usually solve both of these types of issues. See the chart below for more common Nutrient Antagonisms.
Nutrient in Excess
|NH4, K, Ca, Mg, Na||K|
|K and / or Ca||Mg|
|PO4||Fe, Mn, Zn, or Cu|
B = Boron
Ca = Calcium
Cu = Copper
Cl = Chlorine
Fe = Iron
K = Potassium
Mg = Magnesium
Mn = Manganese
Mo = Molybdenum
Zn = Zinc
NO3 = Nitrate
SO4 = Sulfate
PO4 = Phosphate
NH4 = Ammonium