Pleached Plants and Standards
You are thinking about making a considerable investment in your garden and you need some help to make sure you aren't going to make a blunder, so read on.
First thing is to consider is what you need these big plants for and your relationship with your neighbours and if you have them how it will be received. If you think they are going to love the idea and want to help maintain the hedge/screen then you can use pleached trees right up to the boundary and they are very good at saving space. You can garden under them whilst still blocking out a view. If you think, and it is nearly always the case, that you will be looking after them yourself you must leave room to get to the back to allow trimming. That's your choice and depends on your stature. A tall thin person will need less room than a short person needing step ladders.
If all you want to do is hide and help make last an ugly fence or wall you could use the wall frames. They instantly take you out of that imprisoned feeling that 6 foot fence panels create without gobbling up 6 feet of border, which is what a laurel hedge can do if you don't keep it hard trimmed
Now for planting pleached trees. We always recommend that you erect a rail to sit about 2/3rds the way up the clear stem. eg; 2 metre stem rail at 150/60cm off the floor. The rail can be independently secured buy a post every 2.5/3m. If you are in a very windy spot use a second rail midway between the top and the floor to give the plant more anchorage and reinforce the support posts. To the face of the rail you need to fix rubber tree pads and belts to stop the rail rubbing the trunk and to strap the trunk to. (make sure the nails heads are sunk into the pad so they don't scratch at the bark) Best to do this once you have positioned the plants and it's a good idea to know where you are going to be digging the hole for the plant as you don't want to be digging where you have just banged in the posts. Some people like to leave the plants in big planters or pots, the same method of support is best used for them as well. Posts are more important to get in the right spot than the rail, as you can simply over or under lap the rail when starting the next rail. Position the plant upright and fix the pad and belt and you're all but there. Sometimes the frame incorporates the cane or post that is already in with the plant. If it's part of the structure, leave it and tie it in with the trunk to your support frame, if not choose yourself if it is needed or not.
Pleached wall frames. They hardly need any support especially if they have a wall or fence behind them.
Standard trees should be planted much the same way as the support rail method but they can be don separately with 2 posts a short rail and the same pads and belts. They look like mini rugby goals with the tree in the centre.
Looking after them and getting them established.
For the first season you will need to tie in the branches at regular intervals to get them used to the shape of the frame and trim off spare growth you don't want.. Once these branches strengthen up and you have the effect you are lookig for you will be able to clip the next seasons growth a couple of times a year to keep them to the shape you desire. Feed them in the spring taking care to read the instructions on the rate of application and give them water when they need it. Obviously if they are in pots you will need to do this far more often.
Very good luck and feel free to phone and talk before you get into any difficulty.