I have had to trim or remove those things because they get too big and take over an area. What I had to do was use an 3 legged ladder and use a small chainsaw to shave off the tops to a consistent height. It does look a little sparse up there for a bit. To trim the sides again a chainsaw. That would be a huge task in your case. If you get ice and snow build up they tend to break when they get too large. Or die off and leave a big dead plant in the middle of your hedge.
I know what you mean about them rooting themselves in the ground. What I did there was saw them off close to the trunk. Again a whole lot of work for your project. I have trimmed them at any part of the year and had them recover. They do recover faster in the spring. By the way bee's and birds love nesting in them. As others said don't take more than a third at a time. Some of the people that I have worked for were just so tired of cleaning up after them they had me cut down entire hedges and went with something else.
Good luck and be safe.
Chain saw uhh?:laughing: at myself! I was going to purchase the trimmer attachment for my stihl pole saw, but decided to wait until I get some experience with the hand shears first. Don't quite trust my eye/hand coordination yet. A stringline would be a minimum for me to go that route. Another reason is I'm not so sure I want the sheared effect...
Re: 3 legged ladder -aka- an orchard ladder...yep it's a must have for Arbs of this size. I recently bought a 16'er and it's a godsend!
Good to know that it's ok to trim the lower branches that rooted themselves...thanks! I was going to cut them like you mentioned but decided to wait until I found out more. Everyday I learn a bit more about the causes and effects of caring for these monsters. It's been almost 2 weeks since I started thinning the smaller ones and I can see the difference. I may wait until early fall to try my hand at shaping them. For now I have my hands full with just thinning.
Birds and bees love mine as well. But lets not forget snakes and rabbits. Only a few snakes over the years, but rabbits...whew boy!! Dang things love to hide inside and my GSD goes bonkers wild trying to chase after them! She launches so quick I'd swear she's airborn, but has yet to catch one. Don't mind the birds and they don't appear to cause any harm. Their singing in the early AM is refreshing. Now for the bees...hate em! It's been cool and damp lately and since the bees are kinda lazy/dormant during this weather, I pluck off any hives I find. Years ago on the outside of the mature ones, I found a hive that was as big as a basketball!!! Scared me silly first time I saw it. Took a few mins to figure out what it was. The following fall that sucker was history. I keep a close eye now.