I live in PA (Zone 6a) and several sources told me to plant my moonflower (Ipomoea alba) at the same time I plant tomatoes--i.e., when the temperature is above 50º at night.
I did that, and the results are terrible. My plants look rough, I presume from the too-cold nighttime weather.
In areas that don't get above 60º at night until July or August (if at all) there is probably not a good way to grow them because they need a long growing season, warm temperatures, and they have both a short day photoperiod and a need for warmth (that's the same reason planting them super early indoors won't necessarily speed up blooms).
