Pleaching is the training of trees to form a horizontal framework above the ground. Basically, the effect is that of a hedge on stilts. Pleaching is not exactly straightforward: the right type and size of trees have to be chosen for the job, a sturdy framework built, and every year the trees have to be pruned and trained along the framework. Not only is it a lot of work, but it can also take a bit of time before the desired effect is achieved. No wonder then that it never caught on in North America. However, it's still very popular in Europe, perhaps because here it is grounded in a long tradition of use. Since medieval times, pleached trees have played an important role in gardens, mainly to create walkways or enclose spaces such as kitchen gardens.
Pleaching is a very architectural feature, which allows for an interesting space division at a higher level than a hedge. By using plants to create this division, the feeling is lighter and less overpowering than enclosures created with hardscaping. It’s a great way to raise the garden up and define 3-dimensional space on a comfortable, human scale. As with any garden design tool, there are many good ways of using it, and just as many bad. Here in Belgium, I've mostly seen it used to create privacy in front yards where a high wall would obviously be impractical. I think the look works well here because it's used with either older buildings or very modern ones. In between, one might have to be careful so that it doesn't look out of place.
Here’s an example that I watched being put up just this summer (it's on my way to work). The trees are so thin at this point they’re barely visible. It'll be interesting to see how long it takes before it actually looks like something.
This one has probably been in place for a few years and is growing well.
This example in a front yard looks like it’s in need of a trim. As shown here, pleached trees are often combined with a hedge at ground level.
A neat design tool that could offer some interesting opportunities for creative and unconventional use.