How long does it take for plants to respawn?

Has anyone determined the length of time it takes for outdoor alchemy plants to respawn and if there are any gotchas to the respawn?

I did have a look around but all I can find on the web are a bunch of non quotes from people who don't seem that sure.

The contents of a Cell gets reset (respawning everything in it) after 10 days (240 hours) after your last visit.

Well, for normal outdoor plants the others are right. Thing is, with Hearthfire if you have a garden at your house ( I think it is the same with the greenhouse too, but I havent made one yet) it is every 3 days, so plant, go wait 3 days in your house, walk out your front door, (for the loading scene) pick and repeat. Everything in your house that is out in the open (such as the ore down in the cellar if you have the smelter) will respawn like every 10 days if you travel somewhere and come back to it. You will know that the stuff has respawned, because all of your internal doors will be closed.