User blog comment:Woest/Great Tree Arc and Green Magic/@comment-4829046-20131125080227/@comment-7418318-20131125102327

I agree with Woest.

I think the ability to let plants grow rapidly and in the shape he desires works for any kind of plant, or at least any kind with sufficient sturdyness.

Considering that Walrod was in his vegetable garden when he created the plant to transport the Fairy Tail mages, it makes sense that he'd use something that was in his immediate surrounding as the source, like beans.

Or maybe he chose beans over a tree because they are more lastic and thus better suited for transportation.