I have a few plants onboard, and I kinda dig them. I sail with them too... usually one sits in the beer holder by the wheel. They are indoor plants, and my rule is unless I'm mid-project, I want to be ready to sail in 20 minutes or less... so the plants have a place.
I think I'm going to make a planter that resides on the post that contains the cable for the centerboard. It'll be right under the leaking deck
hatch, so it'll stop the rain from getting on my table.
One of the plants on board right now is a cactus... I can advise you against having a cactus on a boat (completely not my idea, and I threaten to teach the thing to swim everytime it bites me)! But it has character.