Last year we planted potatoes in gunny sacks, to which we continued to add layers of dirt as the plants grew, about 24 inches of added dirt altogether. We expected to harvest potatoes at all levels. Didn't happen. They grew small and only at the bottom level.
So this year, on Feb. 15th (as I recall), we planted in tubs. We put rocks in the bottom of the tubs, covered with about 12 inches of dirt. We placed the spuds, sprouts facing upward, about 3 or 4 inches apart, and covered them with about 5 more inches of dirt.
We were advised to test the soil for phosphate levels, but didn't do it this year. It's a trial and error learning experience, eh?
Our remaining winter crops, broccoli and kale, are both doing well. We harvest the kale often, as Robin likes to put it in salads, stews, and soups.
The purple crown broccoli seems nearly ready to harvest. We're not sure why some of it has this yellowish color. Have to do some internet research on this one.