I add 1/4 tsp Epsom Salt to every gallon of water that hits my roots. (For plants 1-2 weeks old, I do 1/8 tsp). In addition, I feed 2-4 ml (gal) calmag (Botanicare, but there are other brands).
I feel like the salt is more immediately available, the calmag more long-term (plus it has calcium).
The reason I got into this mode is that I also give 2-4ml of Silica Blast. I've read calcium and silica can interfere with each other. So, I alternate silica and calmag between waterings. I thought Epsom salt would be good in the absence of calmag. At least the plant would get the mag (but no cal). I alternate until a couple weeks into bloom when I stop silica. I then do calmag and epsom in each watering (until water-only cleanse). I figure fast- and slow-acting magnesium is beneficial during this time because bloom seems to bring on calmag deficiencies(?). That's also when I bump the calmag up to 4ml/gal.
I've read that Epsom salt is a salt and can have negative effects on the soil over time. But, for a 10-12 week grow, and giving such a small amount doesn't seem bad. I water with 20% runoff so I'm getting good flush. If someone waters only until they get a little runoff they might have more salt buildup than not using epsom(?).
they discussed just that :Sharing One:
