Apparently I'm treating my Mealwood really well...
In particular, note the "Quality of Life: 4" as part of the plant's description. While I don't know the exact trigger, the QoL value will change to match that of the last selected Duplicant.
As a result, the Mealwood plant appears to be quite the valued member of the community! It even has friends that it talks with, apparently. I guess those "Meal Lice" on the plant have their own little collective and bathrooms?
There may be more required, but... Select a Duplicant and look at his/her "Quality of Life" value. Select a farmed Mealwood plant (in my case, in a Planter Box) and check out its Quality of Life; the value and its hover text should match the previously selected Duplicant's.