I was talking to my son the other day, and he was considering planting potatoes in his greenhouse, and wanted to know what I knew about doing this.  "Precious little" is really not the best answer, but it was the truth.  So, I looked it up and thought that I would share what I found.  The first place that I looked was our MG Handbook, pgs 395-396, because I knew it would be there.  Then I looked at GardeningKnowHow.com because that is one of my favorite places to look.  But be aware that you can head deeply into the rabbit hole of potato planting sites if you are so inclined.  Since he asked about growing in the winter in the greenhouse, I will mostly concentrate there, but for outdoor growing, this is the short version of the process.  It is best to buy seed potatoes from a nursery that are labeled "Certified Seed Potato".  The reason for this is that they are certified to be free of disease pathogens, and if you are growing from a grocery store potato, there is no guarantee that the potato hasn't been exposed to something along its path.  Plant outdoors when the soil temperature reaches about 45 F, usually February or March.  Cut the tuber into about 2 ounce pieces and let dry at room temperature for about 3 days so that the pieces form a callous.  Prepare the sandy, loamy soil about 12" deep and plant the pieces about 3" deep and 6 to 12 " apart.  Closer planting yields smaller potatoes.  Apply Nitrogen fertilizer frequently as potatoes need a lot of it.  When plants emerge from the soil, apply another 3" of soil and make furrows between the plants.  When the plants are 4 to 6" tall, pull about 3 to 4" of soil up around the stems again.  Keep layering the soil up so that the potatoes are not exposed to the sun.  It is important to maintain even moisture in the soil for proper growth of the potatoes.  When the foliage dies back, it's time to harvest,

 

If you decide to grow potatoes from a grocery store potato that has sprouted in the bin, they are safe to eat, but it is safest to grow them in a container and then discard the soil and sanitize the container at the end of the growing season.  A 5-gallon bucket or plastic tote about the same depth with holes drilled in the bottom are the most commonly suggested containers.  Work the soil down to at least 12" with plenty of compost or slow-release fertilizer.  2 days before planting, cut the potatoes into pieces containing at least 1 eye and then allow them to dry.  Smaller potatoes with 1 or more eye can be planted whole.  Plant the pieces near the bottom of the container with the growth facing UP.  As the plant grows, layer soil and straw around the stem.  Make sure to keep the soil evenly moist.  The potatoes grow along the stem.  When the foliage dies back, it is time to harvest the bounty.  The easiest way is to simply dump out the container and get the potatoes off the stem.  It is recommended to "cure" the potatoes for 2 weeks before eating.  Here, I had to go looking again for how to "cure" them.  I found the most concise information on growingveg.com.  To "cure" them, remove excess soil by rinsing lightly then patting dry.  Cover them to block out the sunlight and store at 45 to 60 F and high humidity for 2 weeks.  Most commercial growers have big refrigerators for this.  During this time, the skin thickens and minor cuts heal.

 

Potatoes can be grown year round in a greenhouse, either heated or not, in containers using the above process.