I bought plants of both in the spring (well, I thought I was buying tubers, but both arrived as plants) and put them in the same
raised bed a couple of feet apart with some
trellis support. The lathyrus is growing okay, though not quite thriving. I think the afternoon sun in that location might be a bit too intense for it. Both were attacked by slugs due to the very wet weather after planting. The lathyrus weathered the attacks, the apios looked to be recovering but then completely disappeared. :(