I would be careful with using Epson Salts each year since salts do not leave soil for a very long time and can make soil toxic.
Feeding your garden beer, coffee and epsom salts: Do they really work
Updated Jan 13, 2019; Posted Jun 11, 2015
By Bill Finch
I'd like to blame the internet for making such a senseless sensation out of Epsom salts. But the honest to goodness truth is that gardeners have been crippling plants with Epsom salts for generations.
Plain and simple, no garden soil will ever benefit from Epsom salts, which is a common name for household products containing magnesium sulfate. If you're lucky, the use of Epsom salts in your garden will merely be a waste of good money and time. In the doses used by most gardeners, however, Epsom salts will promote soil toxicity, often leading to ailments like blossom end rot, serious and long-term potassium deficiency, and sometimes (if enough is used) outright death of the plant.
Yes, I know your grandmother used Epsom salts to water her potted plants. Fortunately, she couldn't afford to use very much. In containers with poor, depleted, acidic soil that is poorly fertilized, there may be some very minor and temporary benefits of a tablespoon of Epsom salts once every year or two, and maybe that's how all of this got started.
But plants need only a tiny, tiny drop of magnesium, and it's a rare soil that is actually deficient in it. To avoid magnesium toxicity, the calcium content of the soil needs to be at least 10 times higher than the magnesium. Adding Epsom salts without adding calcium can really throw things out of whack (and I suspect that's why people who use Epsom salts regularly on their tomatoes often complain about blossom end rot).
Sometimes, soils that are too acid prevent plants from using magnesium efficiently. But the best and only long-term remedy for that is to add organic matter or garden limestone or both. When organic matter breaks down, it lessens the acidity and promotes uptake of minerals. Garden limestone contains a nearly perfect balance of calcium and magnesium, so it never results