I planted arugula this year and a bunch of it bolted and I didn't get around to pulling it for a long time, and when I did, one of the bunches had a huge root, as big as a good sized beet, maybe 3 to 4 inches in diameter.
I believe that arugula roots are edible, but is that still true when the root is that large?
Yes, it's edible regardless of its size. I'd imagine however that just like the leaves, the roots get probably more bitter as they age. With that being said, the biggest reason why its roots aren't commonly eaten lies in the fact that they're usually small and particularly hard to clean. Once you do clean them thoroughly, though, they can be eaten just like the leaves.
