Roof gardens are tough places, and especially with plants in pots, the conditions can be challenging. It is sometimes hard for plants in a relatively small volume of soil not to bake at their roots, and get overexposed. Not sure how big the pots are, but here’s an interesting thread from the University of British Columbia Botanical Garden bulletin boards about wisterias in pots–and as you will see, there is a difference of opinion about how it fares. In your relatively warm climate, the pots must be very large, even if you water regularly, to insulate the roots sufficiently and prevent stress to the plants. (This is all assuming your leaves don’t show insect damage or anything as well…I think you are talking about them just withering, yes?). Link follows:
Welcome! I’m Margaret Roach, a leading garden writer for 25 years—at ‘Martha Stewart Living,’ ‘Newsday,’ and in three books. I host a public-radio podcast; I also lecture, plus hold tours at my 2.3-acre Hudson Valley (NY) Zone 5B garden, and always say no to chemicals and yes to great plants.