what kind of dosage with Epsom salt if I use as a spray directly on the leaves. autoflower week 6

Normally around 1 table spoon for 5l/1gal water. For soil drench and foliar. I would advise against spraying anything on your plant when it is in flower as it tends to cause more problems than it solves. If you need calcium you can make WCA from eggshells. Don't buy stuff for your plants if you don't have to. They don't have shops in forests and all the plants are happy. ;)

One thing to note is that leaves do not absorb things on their top surface its via the stomata on the underside of the leaves. so if you plan on foliage feeding it, have to hit the underside of the leaves. Over all its best to feed the plant via the roots vs leaves. its how it works, its what it have evolved to do, its 1000x more efficient. I would honestly just grab some CaMg from a hydro stop if you are close to one. Mine has mini bottles 125ml and its perfect for little things like this. 9$ Or making your own like Ultraviolet suggested is good, but if you have access to calcium nitrate you likely have access to CaMg solutions premade, bit more stable and would last longer. PS. get w/e is cheapest. when you buying components like CalNitrate or MagSulfate they are all the same. I get my MgS04 from a drugstore as they sell 4KG for about 10 bucks. way better price point then the 500G bags at my grow shop for 12.99 all the same thing USP grade. Good Luck!

Homemade Cal-Mag supplements, using Epsom Salts (magnesium sulfate) and Calcium nitrate (a common fertilizer). The ideal ratio is two parts calcium to one part of magnesium. A safe homemade Cal-Mag concentration would be 380ppm, with 260ppm Calcium and 120ppm Magnesium. For reference, you would need around 6g of calcium nitrate and 4.5g of Epsom salts per gallon of water.