I use it a tablespoon to the gallon as a booster several weeks before I expect bloom. I use a teaspoon to a gallon once a month with my normal fertilization. I'm not exactly sure what magnesium does. I think it helps the absorption of calcium, at least it does in humans. Jack Peters of the fertilizing company says that you can't overdo with epsom salts. He says the plant will take what it needs and discard the rest.

Magnesium has varous roles in protein/nucleic acid synthesis and as an enzyme cofactor but probably the main reason it's important in plants is that it's the central ion in chlorophyll. Magnesium and potassium have been shown to inhibit each other's uptake although increasing potassium supposedly has a greater effect on magnesium uptake than increasing magnesium has on potassium uptake. Therefore, adding a bit more epsom salts when you use a bloom booster might be worth considering. While potassium affects ability of the plant to take up magnesium, magnesium merely seems to compete for binding sites in the media. Presumably the concentration of magnesium and potassium used for orchids wouldn't be sufficient to limit each other's absorption into the media so unless your are really overdoing the epsom salts, I wouldn't think adding a bit more magnesium would affect the effectiveness of the bloom booster.

Thank you corymbosa for the great tip that magnesium and potassium mutually inhibit the other's uptake in plants. alvin

What about using water which has been softened using Potassium?

Jane