I want to create a mini hedge of three Bobo hydrangeas and was wondering about the spacing. How wide do they grow--3 ft? 4? Just wondering if 24 inches from centre to centre will make a good hedge, or if that's too close. 30 inches? 36?

If I can keep them under 30 inches apart then I can squeeze in another, different shrub at the end.

Z5 (Toronto) in a spot that will be marginally full sun (about 6 hours) next to a driveway.

Thanks!