Growing Sweet Potato Slips and Rooting Lemongrass

I thought I would have another go at growing sweet potato slips.  I tried this a couple of years ago and got some roots but I didn't get any slips by the time they needed to be planted on and I abandoned the project.  This time I started just before xmas and as you can see there is a tiny white root developing. 

 Next to the sweet potato is some lemongrass from the supermarket that i'm rooting. 

The sweet potato now has slips but they are small and taking their time.

Hopefully the forthcoming good weather will push them on a bit.  The roots are looking good but I'm wondering whether to put the whole thing into a pot of compost until the slips are a bit bigger. 

 Any advice would be appreciated.