Since no plants use N, P, and K in THE 1:1:1 RATIO supplied by 20-20-20, you can do better. Supplying fertilizer in the ratio at which your plants actually USE the nutrients offers some significant advantages, not the least of which is the ability to keep the level of dissolved solids (fertilizer/mineral salts) at their lowest w/o having to suffer the effects of deficiencies. After the calculations are done for how P and K are reported on fertilizer packages, you'll find that 3:1:2 ratio fertilizers like 24-8-16, 12-4-8 (Miracle Grow makes All Purpose fertilizers in these NPK %s) or 9-3-6 supply NPK at almost exactly the ratio at which the average plant uses the nutrients. I use Foliage-Pro 9-3-6 by Dyna-Grow almost exclusively for that reason and others, which include the fact that FP 9-3-6 includes ALL essential nutrients plants normally take from the soil (including Ca & Mg which most soluble fertilizers lack (MG 20-20-20 lacks these elements/nutrients) and FP 9-3-6 gets most of it's N from nitrate sources and no N from urea. The later fact helps keep plants compact and full. Also, your nutrient supplementation program is usually dictated by your soil choice and watering habits. Soils that retain too much water (like most off the shelf brands) require much more attention to detail than soils that you can water freely w/o concern that the soil will remain soggy so long it impacts root health/function. Root health is a key factor that determines whether or not a healthy organism is even possible - to the degree that good root health is a prerequisite to a healthy plant. Never apply Epsom salts willy nilly, that is to say w/o good reason. Unless it has been determined your plant is suffering a Mg deficiency OR there is an excess of Ca in the soil causing an antagonistic deficiency of Mg, you're probably 10X more likely to create limitations than resolve them by adding Epsom salts. You might find this Basic overview helpful. It will help you avoid all of the most common issues all container gardeners encounter early in their journey toward greater proficiency. Al

Magnesium issues can be a problem on some plants and a cause of chlorosis on unfertilized or underfertilized ones occasionally and hardly a myth, but certainly quite uncommon. You can look up the symptoms online, but as a general rule, any time plant leaves start to yellow, it's time to do some digging (so to speak!) So I keep a small bag around and have for the last decade, but I can absolutely state I've used about five ounces out of it in that decade, including the entire property of 12,000 square feet total. If you're using most versions of Miracle-Gro to fertilize, Mg shortages shouldn't be much of an issue, nor should any lack of green leaves. But still, underfertilization may occasionally rear its ugly head. As a general rule, low nitrogen, iron, or magnesium problems can all be a cause of yellowing leaves (among many others, but those tend to be the primary resource-related ones, in that order), so definitely go investigate if these are showing up on your plants. But never, never blindly toss Epsom salts or any other resource on plants just to cure a problem that isn't there. Magnesium can cause tightening of soils, even very loose and sandy ones, and that's the last thing you want in a succulent pot or any other soil. Too much magnesium also make it harder for the plant to absorb some other resources if amounts rise too high due to simple resource antagonism. I tend to follow the "feed weakly, weekly" method on most plants during their growing seasons because simply put, it works and maintains a constant regular flow of nutrients. If the plant doesn't want it, it has ways of letting you know. If it does want it, it also has ways of letting you know--usually by not growing and turning funny colors. I'd rather avoid that, thanks. But I also tend to avoid that on anything but N, P, and K and only allow maintenance levels of anything else to avoid some of the discussed problems above. So you can walk a fine line over the years even feeding regularly. That's why regular repotting is recommended--and why some of us do some organic feeding even in our pots.

My grandmother, who taught me most of what I know about gardening, put a tsp. into her watering can (2 gallons) every time she watered her flowers. I usually use a tsp per gallon once a month on my blooming plants, and on plants that are looking poorly. I don't want to start the "Epsom salts doesn't make roots grow" argument, so I won't go into what I was taught in college or told by the FL extension service guy, but I know that if plants' roots in Florida hit hardpan and start looking poorly, putting a cup of ES around them seems to help a lot. This is especially true for gardenias, for some reason.

Epsom salts copntain magnesium salts, something in low amounts in our S'Western alkaline soil. Magnesium is an important trace mineral for growth of plants. Epsom salts are an inexpensive rapid Mg replacement.