As far as MG goes I've used it alot. Surly not the soil. It never drys out with the polmyers they added for water retension. But the fert MG is 'cheap' and when you use like 50 gallons water in a watering, its not cost effective not to for my outside plants. Rememeber these plants are weeds. Weed really love decent soil and lots of fert's. Here's a MG I have flowering out back;
Whatever you use and MG is alot better than nothing. You need some micro nut's that MG doesn't have but alittle cal-mag and a budd fert' seen to round it out Keepem Green
Whatever you use and MG is alot better than nothing. You need some micro nut's that MG doesn't have but alittle cal-mag and a budd fert' seen to round it out Keepem Green