I went back after a while and this is still the case. On the 4x4 grid the final two spaces are blank and hoeing, watering or harvesting makes no difference. Also gardening is much, much worse than in previous tests. The lag was so bad I gave up on Chrome and tried Firefox. That worked much better. I'm on Windows 7 btw.
I ran into the same issue, but with Mac/Chrome. Gardening was slow enough to be prohibitive. I saw comments to the effect that it's been a neglected part of the UI, but it sure does help bulk up on energy-rich food before heading out on a long quest or to contribute to street-building.
Gardening has been due for a major overhaul for a while now. Originally we were going to try to get it by the start of this month, but a number of other things have managed to sneak in at a higher priority. We do plan on finishing this in the next month or two but for now I'm not sure if we're ready to dedicate any resources to fixing it at all. I'll check with the dev team.