Zucchini - Rooftop 0, Garden 4

I still don't know why, maybe wind, maybe excessive heat but the zucchini and cucumbers do not thrive on the roof. They do thrive in a traditional ( in the soil on the ground). I have no viable zucchini or cucumbers on the rooftop but after two weeks away, I have lots from my garden on the ground. Zucchini bread anyone?