It’s true. Plants growing on the tops of concrete covered rooftops in the sweltering heat island of Manhattan appreciate a little dihydrogen monoxide every now and again. One of my client’s in midtown west inherited a terrace full of a hodge podge of planters from the previous unit owner. Phase one of making the space his own was to make the existing plants happy. The addition of a fully automatic irrigation system turned his terrace into a brand new place.
Rooftop gardens need watered every day. They don’t take holidays off, and they certainly don’t rest on Sundays. If you don’t have an irrigation system, consider adding one as a smart investment. Multiply the number of years you intend to keep your roof garden by 250 (days of growing season) and then muliply that by the value of your own time. I think you’ll see that it makes sense to get it.
Just one month after installation, I already saw huge changes in the plants which were previously hand watered. Even this Cotinus pushed out a new bloom in August which normally would have emerged in June. I would say we are heading in the right direction.