The Great Sweet Potato Experiment

Last year we grew sweet potatoes for the very first time, and had a very successful crop. Sweet potatoes grow from "slips", which are small stems that root from sweet potato tubers. Last year we ordered our slips from Burpee over the web, but the year before we had difficulty acquiring viable slips and didn't end up planting any sweet potatoes.  For this year, we resolved to grow our own slips.

Over the winter, I went in search of organic sweet potatoes that had not been treated with a growth retardant.  I also wanted to know what kind of sweet potatoes we would be planting.  I went to several winter farmers' markets and talked to several farmers.  They all tried to talk me out of our plan- they did not grow their own slips and believed it to be very difficult.  I finally was able to buy 10 Covington sweet potatoes at the Somerville Winter Farmers' Market from North Star Farm in North Dartmouth.  These sweet potatoes were extremely large, and might not have been the ideal sweet potatoes for our experiment.

There were many recommended ways to grow sweet potato slips that I found, and we decided to experiment and try several different growing techniques.  The one constant was the recommendation that sweet propagation was helped by heat, so those of us who had heat sources used them.  3 of us took sweet potatoes and attempted to grow them in water, and I took 6 sweet potatoes and grew them in a variety of materials:  3 in potting soil, 2 in coir, and 1 in sand, all on a heating pad.  The one thing we didn't try was to cut the sweet potatoes in half before putting them in a planting medium- I didn't discover this recommendation until after the experiment started.  I planted the sweet potatoes sideways with the planting medium about halfway up the sweet potato, and the people who suspended the sweet potatoes in water tried to make sure that the root end was down.

At first, it seemed like the experiment was a complete failure.  The sweet potatoes did nothing, for weeks on end.  I kept them watered, and made sure that they didn't get too much water that would cause them to rot.  The people who had them in water reported that there was something of a white fuzz on the sweet potato, but it didn't lead to anything.

Finally, one of the sweet potatoes in potting soil started showing signs of life.

Once the sweet potatoes started sprouting, they just took off.  2 of the 3 that were potted in potting soil sent up small forests of sprouts, and then the 2 potatoes in coir started sprouting.  The sweet potato in sand was next, and finally, the last sweet potato in potting soil started sending up sprouts.  It seemed pretty clear that the sweet potatoes in potting soil sent up the most sprouts in the shortest amount of time.

The slips got big enough that it became time to twist them off and root them in water.  This seemed like a terrifying task that could easily destroy all my hard work, but it was actually really easy.  The slips weren't that hard to detach, and if they were (mostly because I had let them grow too tall) yanking them off didn't seem to have any serious side effects.  I soon had many slips sprouting in water.

Meanwhile, most the the sweet potatoes sprouting in water were still not showing any growth.  Elisabeth transferred her sweet potato to potting soil, and finally had some success.  

Michael was the only one who managed to have success with sweet potatoes in water.

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I wanted to update that my single sweet potato produced about a dozen bushy slips, but stopped putting out new ones when the heating pad was removed. The slips grew about an inch of roots in the first week when transferred into water; after another week or two, they were ready to transplant into the garden.