Mary's Veggie Garden

January 20, 2014

Sweet Potatoes: Which end up?

Filed under: Vegetables — marysveggiegarden @ 9:39 am

Many people arrive at my blog by searching on “Which end of the sweet potato goes up when rooting in water?” This is useful to know for growing your own slips. The top of the sweet potato produces slips, while the bottom produces roots. Commercial slip growers plant the mother sweet potato horizontally and bury it completely, so they don’t worry about which end goes up, but planting horizontally takes space most home gardeners don’t have indoors while growing slips.

Frazier White Sweet Potatoes - root end is down

Frazier White Sweet Potatoes – root end is down

The standard answer is that the blunt end of the sweet potato is the top and the end tapering to a point is the bottom. This is nicely illustrated by the left and middle Frazier White sweet potatoes above. It is not so easy for the tuber on the right but I know which end is the top because it was growing at the surface and the exposed skin turned a bit green.

Last fall I decided to get the definitive answer. While digging my sweet potatoes I tried to leave the tuberous roots attached to the vine. I managed to dig at least one good cluster for four of the five varieties in my garden. And during the digging of 89 pounds of sweet potatoes I gradually realized why it is so difficult to determine which end of the sweet potato is the top.

Click on any photo to see it full-sized. Look carefully at tuber shape and the stems and roots.

Georgia Jets

Georgia Jets Sweet Potatoes

These Georgia Jets look quite symmetrical top to bottom. Only two or three still have any root at the bottom. The slender roots are quite brittle and break off easily during harvest or cleaning. (Also, I have a habit of removing thread-like roots while washing.) Notice that the stem attaching the tuber to the vine is the same thickness all the way up while roots become more thread-like.

Korean Purple

Korean Purple Sweet Potatoes

Korean Purple sweet potatoes tend to be very long and slender. The tubers taper at both ends. The stems are almost as thin as the roots. Note: the middle and right clusters were the last slips planted in mid-late June and they needed more time to develop. Although undersized they were still good eating, baked in their skins and eaten as snacks.

Purple Sweet Potatoes

Purple Sweet Potatoes

Purple sweet potatoes tend toward plumpness. Their stems are thick.

Laceleaf Sweet Potatoes

Laceleaf Sweet Potatoes

Laceleaf tubers tend to grow knotted together. It is often difficult to find a straight tuber that will fit into a container for growing slips. The tubers taper at the top and the bottom is blunt.

What conclusions can be drawn from all this?

  • There is no hard rule for determining the top of a sweet potato tuber. The tuber may taper at the top or the bottom or at both ends or it could be blunt.
  • A given variety may have a tendency towards a particular shape. Dig clusters and take photographs during harvest so you have the information in the spring.
  • During harvest try to leave a bit of both the stem and the root on the tuber. That will help months later when it’s time to grow slips. You might tie a thread or twine on the stem end of potential mother tubers because the stem and roots are likely to dry up and break off during storage.

What do I do? Many of my sweet potatoes start growing slips during storage. These slips stay small until I put the tuber into water to root – then the slips actively grow, even before the roots are visible.

L-R Laceleaf, Purple, Korean Purple, Georgia Jets & Frazier White.

L-R Laceleaf, Purple, Korean Purple, Georgia Jets & Frazier White. Baby slips are at the bottom. Laceleaf was stored on top of the refrigerator, the rest were stored at room temperature of 64-68°F. Photographed 1/20/2014.

Without water, slip growth is dependent on temperature – around 68°F most are barely nubbins, at 80°F (stored on top the refrigerator) they grow up to an inch and at 50°F (the temperature of my basement storage room now) the slips die and the sweet potatoes deteriorate. Last winter I ruined most of my Georgia Jets for slip production by keeping them in the basement during the coldest part of winter.

I apologize for not providing the definitive answer, but now you know a lot more about how sweet potatoes grow.

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