In the recent article from Scientific American titled Landscape Influences Human Social Interaction, one study posits that we are more "neighborly" when our yards are covered with lush lawns, not waterwise plantings. But I'll add my own *asterisk to the findings. Because I can't tell you how often I have been out working in our own, non-lawn, garden and been engaged in conversation by neighbors and passers-by precisely because the garden isn't the typical suburban patch of green. Comments usually start along the lines of, "Looks good!" and evolve into "What is that (plant)?" or, quite presciently, "Are you a landscaper?"
So I will say that yes, landscapes do influence socialization. But I'll wager that it's the quality of the garden, not the content, that impels us to be neighborly.