Question
I started my own sweet potato slips early last spring with an organic sweet potato (yam) and planted the slips later. I did a little digging yesterday to see how far along they were and found nothing but a few red roots that looked like little tubers. What happened? I'm in zone 5, if that helps. Thanks!

Answer
Without knowing the results of a soil test, it is hard to say for sure, but it sounds like your soil is lacking potassium, the one necessary nutrient when growing root crops. Next year, I would definitely have your soil tested at your local nursery to ensure proper nutrient and ph levels. For clay soils, many gardeners add lime to the soil to increase the alkaline levels, but I do not recommend this until the ph test is confirmed.

I also recommend planting the slips in well amended soil consisting of compost and/or aged manure. This will virtually eliminate the need to fertilize at all.  Once the foliage begins to brown and wither, the tubers should be fully grown. Dig them by hand to avoid puncturing them with a spade or pitchfork. Since they will keep in the ground for several weeks after maturing, you should wait until the soil dries before harvesting.

Some other tips I usually give for sweet potatoes include spacing the slips 6" apart and covering them with 5" of soil. As the vines begin to grow, make sure you continually hill or mound them with soil or straw to keep the tubers completely covered. Otherwise, the potatoes will turn green and potentially toxic.  

Once the vines begin to flower, stop mounding the soil and start mulching heavily with straw to conserve moisture. Water deeply at least twice per week. Do not fertilize with a high nitrogen fertilizer. This will result in lush top growth and very small tubers.

I hope this helps.  Good luck, and if you have any other questions, please feel free to write again.  

Regards,  

Mike