Replacing trees with screening hedging

There are à double row of lombardy poplars on the side of the main road here they were there when it was a farm before the housing was built just after ww2 they get lopped occasionally but continue to grow each time with new vigour.
Just saying, dump the pine if its a problem but don't trash it all,just because the railway tell you you have to.
I definitely wouldn't touch laurel it's awful stuff, a mixed hedge is OK as long as you have time to wait for it. Maybe hawthorn.

 

A lot also depends on your location and climate @Chris87, and the aspect of the fence, and it therefore affects what hedging or shrubs you plant because some will establish more readily, and grow more quickly, than others. There's a vast difference between north and south in the UK, in terms of weather, and also from east to west. A south facing fence has very different conditions from a north facing one.
Also, what thrives easily up here can be trickier down south simply because of those weather differences. We don't get droughts and hosepipe bans in the west of Scotland so it's quite easy to establish shrubs/trees through summer. Equally, many plants can struggle here as they aren't hardy enough, where they'd grow like weeds in the south east of England.

 

Thanks everyone - most grateful for all of the replies.
I’ve had 3 opinions from tree surgeons, and have instructed an independent tree survey, and they have all recommended removing the trees based on their condition and location.

I’m leaving towards raising the border (about a meter), improving the soil, and then adding a mixed hedge.

I’m hoping this will help the soil recover (I’m thinking adding a mix of quality topsoil and compost?)

in terms of raising the boarder - I was thinking scaffolding planks at the back, and railway sleepers at the sides and front, all lined with waterproof membrane.

Any opinions / advice on all of that would be much appreciated

 

A metre is a really huge amount @Chris87 . It's highly unlikely you'd need to have anything of that size to get a decent depth of soil for hedging. Around 15 to 18 inches would be more than enough if it has a good mix in it. That needs to be mostly soil so that it doesn't sink too much [you can get bulk bags] and you can add grit/finer gravel to that too, so that there's reasonable drainage. Sleepers and/or those gravel boards will be fine. A depth [front to back] of around 2 to 3 feet will be fine for most hedging.
If you get a bed created and filled over the next month or two, you're at bare root hedging season, which lasts until late winter/early spring, and it's a very cost effective way of buying a new hedge, regardless of type. You can usually pre order from around late August, and some might even be ready for that just now. That also means you can buy smaller specimens which will root/establish more easily, and will therefore give a better result in the long run. Around 90 cm is a good size for most planting/hedging. Hopes Grove Nursery and Hedges Direct are both good suppliers, so have a look around just now for prices etc.
Once planted up and watered in, a mulch of bark, compost or similar will help to keep it all happy over winter.

 

A raised bed that high would likely be difficult to prevent from being very dry, and I think you'd struggle to create a structure strong enough to anchor the roots, so the roots would need to get down below it, or I wonder if you could maybe go for a wider construction like a Devon bank to plant on...?

 

I agree with Stephen. Hedges are quite good at blocking rainfall and so you'd need a decent width to the planters to allow any rainfall to collect. The higher you go with the planter, the drier it will likely become and the harder for the roots to get down into the surrounding soil where any moisture might be.