The addition of organic material (compost) to the soil and the use of mulch usually supplies the necessary magnesium needed. The only dilution rate found came from "Rodale's Garden Problem Solver," which calls for 1 cup Epsom salts dissolved in 1 gallon of water and applied either as a foliar spray or directly to the soil.
There are no references that say that this will prevent blossom drop. Blossom drop in tomatoes is caused mainly by temperature. Tomatoes will not set fruit when the night temperature exceeds 75 degrees F or the day temperatures exceeds 92 degrees F.
Contact your local Extension office for a soil test to find out the nutrients your soil contains and what, if anything, is lacking.
