When you buy a bathroom shelf (over the toilet kind) to sit in front of the window so you have more space for those many jars that are full of plants :-)
When you have tanks UNDER your desk with clip lamps attached to the legs for light.
When (while purchasing a new jar/vase/glass) the guy at Salvation Army asks you to show him pics of the planted jar/vase/carafe you purchased last week.
When you buy your boyfriend a case of bottled water on the condition that he save the empty bottles for you to grow moss in.
When you empty a Jack Daniels bottle, you fill it with gravel, moss, and water, then dig up your Peace Lily houseplant, and remove a section to put in the top. Then it becomes the centerpiece of your coffee table.
We might have a winner here.