european hornbeam hedge

good day folks, i’ve bought a couple of the above mentioned hedges and would really appreciate your opinion on how close to plant them together to make an effective hedge. they are already about nine feet tall. many, many thanks…

Carpinus betulus ‘Fastigiata’

I am considering planting 2 Pyramidal European Hornbeam for the purpose of screening. I am getting conflicting opinions regarding planting time. Which is optimal, spring or autumn? How far apart should they be? I live in Oakville Ont. Thank you…