Foliar feeding is an excellent way to feed your plants, and or enhance a typical feeding program. Never used Epson salts as a food source personally, so keen to hear if this brings its own benefits. Typically I supply different feeds for the various stages - for example, a Nitro rich tea during veg, potassium heavy tea during early flower. Most important aspect of foliar feed, is to do so during low light and cool temps - you can very quickly cause damage if you feed in high heat / intense light. Kelp / fulvic acid works really well during pre to early flower. Fish emulsion or any Nitrogen heavy feeds work well in veg. Just be mindful of all that extra humidity that you are introducing - a simple water wash is great to clean the leaves after a few sprays. I stop all foliar feeds late into the season outdoors, and once flowring is well underway indoors. This is to avoid PM and excessive RH during flowering.
