I love tropicals, and in my zone 4b garden, I treat mandevilla as an annual. I usually grow it in the ground, training it up a 6-pole bamboo teepee that is 5' high. This years' plant was not fleshing out nicely, so I direct seeded Cypress vine at the base of the teepee. What a comical pair. Cypress took off in the summer heat with loads of tiny red blooms and now [end of September] all I see of the mandevilla is its blooms jutting out of the cypress vine.
