I used large grow bags last year, two of them, and did get quite a few, but not as many as advertised, more like 7 pounds per bag. Also, many of them were too small to store, and I chose to eat those right away. They stored very well - I still have a few pound left, the last of my 'root cellar' veggies, and didn't need a whole lot of watering. The best part of them was how beautiful the plants were, hence my planting them in that elevated planter, which has housed strawberries one year (gorgeous!) and green beans the next (so easy to harvest!). It's likely to be spectacular planted with purple leaved sweet potatoes! Onions on the west side - I got great onions from that planter last year - and early lettuces on the east side.

I remember that my slips looked even worse last year, and took a few weeks to get going, but they took off after that. I think yours are probably fine. Where did you get them? Mine are from FEDCO, Vardaman variety.