Currently it seems to "work", but it's extremely slow to harvest. I've seen anywhere from 30 seconds to over 3 minutes between each harvest even when all plots are fully grown.

Is it slower than with other plants? This doesn't seem like a bug.

yes, significantly slower. here's a screenshot

But it still works?
Because then I don't see this as an issue.

harvesting one plant every few minutes when there are 9x9 plants fully grown isn't an issue?

The farmer isn't even supposed to support plants like this, as it's said in the manual it's only supposed to be used for basic plants like Wheat and Potatoes.
But there's nothing I can do about this either. It has to be something with the way these plants work that makes them not be usable in the farmer like other plants are.

You know what? Changed my mind. I'll implement this at some point.

Will this also include Nether Wart?