I had some yam peices in pots for over a month sitting on the window sill and they are just now sprouting. I keept them on the dry side because I was afraid they would rot. I think what triggered them was the warmer temperatures, esp. night temperatures. But yeah, they do take a long time.

I got my first harvest, and these guys were only around an inch in diameter, kind of disappointing so I believe they need at least 2 seasons of growing in order to reach a decent size for harvest. Also the tubers will grow a few feet deep, so before growing it, make sure you have a large enough shovel.

Here is a link that might be useful: my gardening blog

I read somebody in San Diego saying this root grows to 4 inches in diameter in 4 years. I collect and cook the small Dioscorea air tubers, they are known as air potatoes and I believe they are the same plant or closely related. Very nice - like real potatoes.

Store bought eating sweet potatoes may have been treated to prevent sprouting. So you have'd better buy it from farmer's market or flea market in order to plant it.

Did you cut the yams into smaller pieces for planting or did
you bury an entire tuber whole? I have some 7" long tubers I'd like to sprout and wonder if I should cut them into smaller pieces.

How to Plant and Grow Sweet Potatoes

http://www.diynetwork.com/how-to/how-to-plant-and-grow-sweet-potatoes/index.html

This thread is drifting away from the original topic, so forgive me if I attempt to clear up some confusion regarding "yams".

Chinese yams are true yams, of the genus Dioscorea. True yams are mostly tropical or sub-tropical vines, although the Chinese yam (Dioscorea batatas) will survive in most temperate climates. As mentioned by KatyaKatya, these vines form small bulbils on the vines (the "air potatoes") which can be eaten or planted.

Chinese yam is also sold as an ornamental under the synonym "Cinnamon Vine", because of the scent of its flowers. It is an aggressive climbing vine, which can cover a shrub or small tree in one season. They form very large, very deep underground tubers, but these require more than a year to reach full size. It's worth noting that the tubers remain in good quality even after several years.

By contrast, sweet potatoes, while often misnamed as "yams" in the U.S., are Ipomoea batatas, and are members of the Morning Glory family. They do not climb, do not form bulbils above ground, and form their underground tubers in a single season. They are not related to true yams.

KatyaKatya, how old are your vines? And how have they held up over your winters?