Firstly plants do not absorb nutrients through their leaves (with some rare exceptions) they absorb nutrients through their roots. Secondly, the amount of magnesium that plants need is very small. Almost all soils have more than enough. If you are growing in containers just use a fertilizer that contains both micro and macro nutrients. The only reason to use Epsom Salts is if you have a soil test that indicates a deficiency in magnesium. To use it otherwise would just allow the excess to runoff into ponds and streams. You need to get your science right.
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