So many super-great responses...!
Knowing that not everyone *can* be inspired to be interested, it doesn't hurt to ask or try to gauge the potential. ...if you really are willing to share your space, as said. :+) If not, having one of those, "I'm going to garden while you enjoy that other thing you like" discussions sounds like a great idea, if not already in practice in the relationship. Then you each have something to tell the other about later, too. (Both are supposed to pretend with equally feigned sincerity that this info is fascinating, exciting. LOL!)
Asking about preferences, like "should *we* (subtle inclusion psychology) do blue or yellow flowers next to the garage this year?" "Would you enjoy this tree or that tree more?" "What would you like to see out there when you look through the window?" After helping to make a few of these decisions, a sense of pride & ownership should develop, should the seed of such potential exist in the spouse.
Most people are fascinated by butterflies. If you get some host plants enjoyed by the butterflies in your area (host plants are those that the caterpillars eat,) and nectar plants (which provide nectar to adults that we recognize as butterflies,) you can get quite a few butterflies fluttering through. (And if so, please don't put chemical treatments on these plants.)
Propagation. If there's a latent plant-o-phile in someone, watching roots and new growth develop on/from a cutting should wake that up.
