Do I Need to Buy Seed Potatoes or Can I Just Grow Potatoes from the Grocery Store?

Buying seed potatoes from a nursery catalog can be pretty pricey and its not really necessary. The only real advantages are that they sort them for uniformity of size (not a big deal), you know that they're ready for planting (see the discussion about dormancy below) and you can find some exotic varieties. We just use potatoes we saved from last year's harvest or buy them straight out of the produce section at the grocery store. 
The term "seed-potato" can be misleading. Potatoes do, on occasion produce seeds, but growers do not grow their crops from them. Instead, they grow them from small sprouting potatoes. Any potato, with sprouting eyes, that's at least the size of a chicken egg has the means to yield up to five pounds of fresh potatoes (Generally speaking, the smaller varieties of potatoes grow to maturity faster but yield less harvest.) 

Potatoes are unique in that their growth cycle is not determined by length of day (as so many other plants are.) Potatoes have an internal clock that requires them to be dormant for a prescribed amount of time--different lengths for different varieties of potatoes. They won't sprout until their dormancy cycle has been reached. This is why some potatoes are better storage potatoes, because they won't start sprouting before you've eaten all the ones you want to eat.

 

When we want to plant more potatoes than we've saved from the previous year's harvest, we start looking for seed potatoes at the grocery store in late January (mid-winter in northern latitudes) and continue to buy them through till mid-spring. Many of the potatoes that have been in storage for the winter start to sprout in the warehouses at that time and you can get them for better prices. When selecting potatoes to plant, look for ones that already show signs of budding/sprouting from the eyes as this way you know they are viable for growing. Choose the variety you like best. Potatoes do not "cross pollinate". This means that, if you plant a russet, by golly you'll get a russet. (Note: one of our favorites is the Yukon Gold. They last a long time in winter storage and we like the flavor/texture too.) 

Potatoes need 70-90 days from planting to maturity so count backwards from your first frost date, or when you wish to begin eating your harvest! The exotic potatoes that come into the markets, and the small, egg-sized, common varieties are usually quite fresh; as they don't keep a long time in storage. They too won't be ready for planting till they naturally go through their dormancy cycle—four to six months. We haven't tried this but I read that you can hasten the dormancy by storing the potatoes in a cool, moist place for a few months and then putting them in a dryer, warmer (but still dark) area.

It is important that you buy organic potatoes because many of the commercially grown ones are sprayed with a "sprout-retardant" which gives them a longer shelf-life and this can delay their sprouting until the potato actually rots.

If the potatoes you have are only just starting to sprout and the buds aren't very long, keep them in the dark to encourage more sprouting. Once the buds are at least 3/4 of an inch long, it's time to "chit" them. (see article about

 

How many to get? Each plant will take up about 12 - 16 inches of row space. If stored well, they will last for up to six months before starting to sprout again. Figure on 3-5 pounds of yield per potato you plant. What size should you get? Ideally you will find them that are about the size of a chicken's egg. Larger potatoes can be cut and allowed to skin over so they won't rot when you plant them.
What if they aren't already sprouting? If you can find potatoes that already have "eyes" that are budding, so much the better. This way you know they are viable for planting. As long as you buy organic potatoes (that have not been sprayed with sprout retardant), and allow 3-4 months time for them to begin to sprout, they do not already need to be sprouting.

When is it time to plant potatoes? Here in the S. Willamette Valley, unless you have raised beds, you need to wait to plant them till the ground dries out a bit. We planted them in early-April one year, when things were especially cool and wet and they just rotted in the ground. Depending on the variety you plant, they take 13 to 17 weeks to ripen. You may wish to plant them in succession so you'll have some potatoes to eat fresh and, the later harvests will last longer through the winter.

 

Storage: If you buy them in a plastic bag, transfer them into a cardboard box or paper sack so they don't rot before you get to them. Keep them in a cool, dark place, with good air circulation until they sprout. Layering them in a tub with leaves or straw, or sawdust works too. Just be sure to keep them from freezing.

Now I also read that store bought potatoes are often "sprayed" to tamp down the "eyes" growing. Right now I don't know what to believe And all I want to do is eat.