A great stocking stuffer is a membership to a botanic garden.
Members enjoy a whole host of benefits, including discounts at local nurseries! Wildwood donates plants to the UC Berkeley Botanic Garden and the SF Botanic Garden. We also give 10% off purchases to members of those organizations.
For people who don't have a backyard, a botanic garden is a great place to wander and even get their hands dirty volunteering with staff at the garden. There's often parties and events throughout the year for members of the garden.