What vegetables are the hardest to grow?

[noorkhurshid]

Wasabi is the hardest vegetable to grow. It requires very controlled temperatures and a high humidity level, but it cannot be stagnant. Since it naturally grows by mountain streams, it is typically only harvested from the wild or cultivated for commercial purposes in Japan

[ETA]

This year, we are growing 88 different kinds of vegetables, flowers, plants, including things we've never grown before.

I try new things every year. 
The previous season, I tried chick peas (garbanzo beans) and that didn't work.
Beautiful plants with lots of great blossoms, but that was it.

The year before, it was okra. Didn't work. Awesome plants, but no okra.

To me, the most difficult so far is Belgian endive (not to be confused with regular endive).
I'll make a separate post about the growing process soon.