Gardeners are generally fond of using Epsom salts as a fertilizer supplement. Epsom salts, as you know, is a hydrated magnesium sulfate. I'm not aware of any effect on combustion. I can't say that I noticed any effect at all of using Epsom salts in my starter trays during one season, although some FTT members find that it helps. I suspect that the apparent effect of Epsom salts as a fertilizer is dependent on the nutrients already present in the soil vs. any deficiencies. When used in a foliar spray, its direct uptake seems to make (rose and vegetable) leaves greener. I don't know what an Epsom salts foliar spray would do for Nicotiana tabacum.Bob, would you think a high application of epsom salts hinders combustion ?
Bob