Cutting back conifers?

I have a hedge row of conifer trees, probably leylandi, and i want to cut the top 2/3 feet off of them to let more light into the garden. They work as a good hedge to keep the neighbours out though. The garden is on a slight slope, about half a meter from one end to the other, so the trees at the far end of the garden are not as tall as the ones close to the house. This means that the dead brown bit will be virtually at the top of the tree when i cut it towards the end of the garden.there is a lot of new growth above the brown stuff which has grown over the last year or so. Would it be ok to cut it down this far without killing off the tree? In the middle of the garden it would be right into the brown bits but i have a willow and some bamboo that covers this bit anyway. near the house it is a good 12 feet tall, all with superb green growth all the way from top to bottom. There is about 30 trees all planted very close together so there will be a lot of waste to get rid of again, i took over 6 feet off my other trees last year and found a bungalow hiding behind them!
Ill get a few pics up later.

 

The red line shows where they would be cut

 

The blue line is where the trees used to be up to.

 

If you take off all the green growth, the tree dies. If it's Leylandii some would say that's a good thing. It sucks all the moisture and nutrients out of the ground, making life very difficult for any other plants you want to grow.

 

Most of them would still have some green bits on them, the ones in the middle behind the other trees would be cut into the brown most by the looks of it but the other trees would mask that bit anyway. I would cut them ones out but then it would look weird having a big gap.

 

Cut them out and plant something else in their place. Or cut them down to the brown stuff and then grow something up them like ivy to green it up, but if you do that just be sure to keep a close eye on it or it will take over.

 

You wont kill them by topping them. The brown dead wood on the sides will never regrow regardless.

Topping them makes them come back with more vigor. Leylandi are unsightly things and deplete the ground of moistures, if possible if you can afford to then grub them out. Otherwise by all means top them but be prepared to do the same in 12 to 18 months.

 

I will be leaving them in untill i can afford a new 6 foot fence, which will be a while. It keeps their kids football in their garden so it wont smash my greenhouse and its good for privacy. If i sit on the patio you cant see the neighbours and they cant see into the garden even from their bedroom windows.

 

I think your Leylandi will be fine if you top it as marked.

The tops will regrow and you willl have to do it again next year.

The brown bits won't regrow but they will still give you a privacy screen. You can grow something else up them.

I used to have a Leylandi hedge. Planted it myself so no one else to blame. Lived to regret it. It was just a fight every year to keep it under control.

 

You can chop the top off a Leylandii hedge, and it will regrow - its only the side branches that won't regrow from brown wood.

I would recommend that you cut it 6" below the final height, then when it regrows (imagine the sprouts in all directions) you can re-establish the top at 6" above.

I hate Leylandii with a vengeance, but I don't have a problem with a smartly maintained hedge like yours. Planting a new hedge is going to take 5 years, or so, to establish so I can well understand why that''s not an option.

 

Got it all trimmed down, took about 3 feet off the ones nearest the house. Heres a few pics of afterwards.