Mine is about 24 by 24 inches. I see you are from Canada. This plant will not survive any prolonged temperature below fifty degrees which won't be too far off where you are I believe. So be sure to move it indoors when the time comes if you can.

Hi, welcome to GoY, Dipladenia are now in the genus Mandevilla, and there are about 120 species, depending on which species you have, 1the height and spread varies, I won't include the tropical perennials, just the climbers, all of which are frost tender, although M laxa may survive short periods of temperatures near freezing, the usual minimum is 41f growing to a height of 10 to 15 ft, most of the species need a min temp of 50 to 59f and grow to a height of 10 to 15 ft, but they don't have much of a spread being climbers, Derek.