Of all of the old wives' tales swirling around the gardensphere, the magical ability of Epsom salts to goose your plants into a Nirvana of health and vigor ranks as #1. Plant not blooming? Give it Epsom salts. Plant not growing? Epsom salts. Plant singing off-key? Epsom salts.
The legendary benefits of Epsom salts aren't restricted to just plants. People cash in too. Fans of Epsom salts claim they speed the healing of wounds, soothe sore muscles, help you sleep, soften your skin, and most importantly, cure constipation. (Eating Mexican food from a street vendor in Guadalajara has the same result, of course.)
Named for the town of Epsom, England where they were discovered in a spring in the 17th century, Epsom salts are a chemical compound called hydrated magnesium sulfate. Magnesium sulfate supplies two essential plant nutrients -- magnesium and sulfur. So it stands to reason that supplied in the right amounts, they'd be good for plants.
People commonly use Epsom salts to feed plants that crave magnesium, including tomatoes, peppers, and rose bushes. They claim that Epsom salts mixed with water and poured around the bases of plants or sprayed directly on the foliage result in more and bigger flowers and fruit.
The thing is, unless you do a soil test, you'll never know if your soil lacks magnesium and sulfur. Dolomitic lime contains magnesium, so if you've been liming your soil, chances are it has plenty already. Plus, magnesium and sulfur are only two of the many vital nutrients plants need. They also require nitrogen, phosphorus, potassium, iron, calcium, manganese, zinc, and other micronutrients. You don't get those from Epsom salts.
So Grumpy's advice is use Epsom salts from time to time if you think your plants could use a kick in the pants, but don't rely on them solely. Also use an organic, slow-release, complete fertilizer, such as Espoma Garden-tone 3-4-4 according to label directions. And build good soil that stores nutrients by adding to it lots of organic matter like composted cow manure and chopped leaves.
What's the correct dose of Epsom salts to apply? For foliar feeding, it's 1 tablespoon per gallon of water. For soil drenching, add 1/2-cup per gallon of water.
One final thought -- you'll note from the Dr. Teal products shown above that Epsom salts can rejuvenate tired plants, reduce stress, and, most significantly, increase sensuality. So if your tomato plants long for more frequent and more satisfying pollinations, Epsom salts could be manna from heaven.