I fertilize potted plants very differently from in-ground plants. Potted plants get watered so frequently that fertilizer is washed out of them easily, so I use a diluted balanced fert pretty much every time I water them. Also the soil in pots is unlikely to build the whole network of microbes etc that is needed to break down the organic fertilizers, so I just use MG or what ever is cheapest.
In the garden, I fertilize organically, composted manure and bone meal mixed in when I plant, then a fish kelp fertilizer several times during the season, plus I mulch the beds with more composted manure.
I have read that to much nitrogen toward the end of the season is bad for the tubers, encouraging them to rot during storage, so I pretty much stop feeding them anything extra at the end of July.
