Well, I like the greenhouse idea. However, it would be quite difficult to simulate so many different environments in a small area on your own. Which is why I think Bob should find some of these for his artifact museum:

Planters of Ellindel (60 cr):
Herbalists that need extra space to plant a plant can purchase and drop one of these large, magical pots. They are imbued with a curious sympathetic magic that transforms the soil within to match the requirements of whatever plant is transplanted inside. This allows plants to grow in areas that are normally inhospitable to plantlife (such as houses), although herbs that grow on different planes would grow slightly more slowly away from the plane they originate on. Note that these must be dropped in order to use, and once dropped, cannot be moved. This artifact is not exchangeable, and does not return to its owner's inventory, so place it wisely!

I think it beats having to build a swamp in your house.

Sounds good, but it should only be usable by the owner or it's kinda worthless.

Drop it in a room only you have access to, like a house or a storeroom and you're done with that problem.

The major problem is that what you propose allows you a way to get herbs without the competition on the outside, which means you get abour 50 of that herb, and people would take the hard to get herbs of course like sparkleberry and horehound, and kinda ruin the market.

The price you put for it is very low too (not sure if that was a serious thought or not) but at 60cr per, people would by 10 pots easily and totaly ruin that herb market.

If such idea is ever put in, I hope it will restrict growing herbs that only grow in that plane to give some control over it.