I would do 6' apart for a quicker hedge; up to 8' apart if you have a decent amount of time to wait. Nannyberry Viburnum here in Iowa has terrible powdery mildew every year that can defoliate a decent amount of the plant so see if it is the same for your area if you are considering including in in the hedge. Make sure to keep the hedge well mulched and grass away from it and they will grow quickly.

Thank you! We have either hot dry summers or wet humid ones. I think I will plant the (possibly) nannyberries elsewhere until they set fruit and I can positively id them. Maybe I'll split the difference on the others and go 7' apart, although I have the time to wait for 8' spaced plantings to fill in. The line I want to make with the hedge is between 60' and 70' feet, do you feel 8 shrubs total would be too crowed when mature? I could plant some elsewhere...Thanks so much for your help!

what I've read, most of the shrubs will be between 8 and 12 or 15 feet wide when mature.

==>>> nothing ever stops growing ... and a lot of peeps use 10 years as maturity ... but a lot of things will be twice as big in 20 years ... nothing ever really stops growing ...

my first house was behind a funeral home ... there were 8 inch trunk Vs ... that were at least 20 feet tall ... and the line of them... ran 100 feet ... i have no recollection of the planting spacing ... nor could i speculate how long they had been there ...

one way or another.. sooner or later.. you will be pruning them to maintain whatever size you prefer ...

for shrubs its called .... rejuvenation pruning of shrubs ...

ken