marijuana survives temps down to about 34 degrees. at this temp however it doesn't grow much if at all. if your region only has temps higher than 60 degrees during the summer than you are going to have to do and artificial flower. Somehow you will have to cover your plants before the sun sets or rises to increase the number of hours the plant is dark. the light cycle controls when the plant grows (vegitates) or when it buds (flowers). in the spring and summer the days are longer therefore it only grows stem and leaf. in the fall/winter the days are shorte and therefore it grows buds as well.
I suggest building a greenhouse that can be covered with an opaque cover.