Well, it's NOT!
Lots of people are trying to use Epsom salts to fix their undiagnosed plant problems, thinking they will make the leaves turn green and healthy again. This is not logical. Why?
-Problems caused by overfert (burns, lockout, increased sensitivity to heat, soil salting) will be exacerbated by YET ANOTHER ionic substance entering the mix.
-Problems caused by overwatering can't be fixed by changing what is in the water.
-Problems caused by pH imbalance are not solved by the addition of another chemical, especially one that can interact with what is already there and make soil chemistry even less stable.
-Problems caused by insufficient Calcium in the water are not solved by adding a Magnesium compound. You have to add CALCIUM.
DIAGNOSE YOUR PROBLEM BEFORE THROWING 'SOLUTIONS' AT IT!!!!!
(no pun intended)
When is it okay to use epsom salt?
-When you have diagnosed your plant as being Magnesium deficient or locked out. The leaves appear evenly striped, with a pale streak running cleanly down the center of each interveinal region on the fan leaf.
-When you are already correcting the CAUSE of the initial deficiency or lockout. This means identifying and fixing all soil, water, fertilizer, and envrironmental problems and actively addressing them.
How should you apply Epsom salt?
-Using a Magnesium compound as a foliar spray is less risky than adding it to your fert solution (unless you have calculated what you need or are using CalMag Plus). Fill a spray bottle with lukewarm tap water. Add one drop of dish soap and 1/4-1/2 teaspoon of Epsom salts. Allow to dissolve. Mist lightly, not to runoff or beading, onto affected leaves just when the lights come on. Repeat daily until pale stripes disappear.