As magnesium only works when there is a deficiency in the diet it may be an idea to look at the soil analysis charts available online, they show clearly where magnesium is plentiful, and where there is very little in the soil (mainly mountainous and hilly areas are deficient). If your area has...
They are all my old favourites too, I`m still buying any that I find that have been thrown away over the years, and have to admit to reading them too! Thank you for the Facebook group, now off to investigate!