Hornbeam "is extremely patient of the knife", as the great garden writer, John Claudius Loudon, put it, which is why it is so extensively used for hedges. At the Chelsea Flower Show this year, Tom Stuart-Smith stretched that patience to the limit by using 30-year-old hornbeams, cloud pruned so that only puffs of foliage were left, balancing at the ends of the branches in a way that I had never seen before.
Like beech, hornbeam (Carpinus betulus) hangs on to its leaves through winter, so that though it's deciduous, a screen of it provides almost the year-round cover that an evergreen hedge of yew does. In leaf, it hasn't got quite the shine of beech, the leaves more deeply veined, but for gardeners it is a more forgiving plant. It will put up with the heavy clay spoils that beech loathes and it is tough enough to stand up to wind.
I like it best when it's pleached to make a kind of hedge on stilts, such as you see beyond the red borders at Hidcote, Lawrence Johnston's garden in Gloucestershire. He'd spent a great deal of his early life in France and certainly it's a feature you see more often in French gardens than you do English ones. Getting that particular effect is more complicated (and costly) than just planting an ordinary hornbeam hedge, but there are places where it can be a useful architectural device.
Say, for instance, you have a boundary wall or fence that is not quite high enough to screen off something you do not want to see. The financial implications of building higher in brick or stone will be even more expensive than pleached hornbeam – and solid walls that are too high can sometimes make the space inside feel like a prison.
So instead of building, you plant, but first you need to get a secure support system in place. At the two ends you need uprights, say 3.7m (12ft) high (or however high you want the finished screen to be). These end posts need to be properly braced, so they do not start to sag towards each other. If you're planning a long run of hedging, you may need another post in between, so that there is not much more than 5m between each upright.
Then you need to strain horizontal wires between the posts, the lowest about 2m (or at whatever height you want the foliage screen to start, the top one at about 3m and the other two spaced evenly in between – so roughly 33cm apart). Really ambitious stilt hedges will be trained out on as many as seven parallel wires. It all depends where you want to start and where to stop. On a seven-wire frame you would be able to grow a stilt hedge with bare trunks up to 2m and another 2m of foliage on top of that. The structure doesn't have to look like scaffolding. Use stainless steel cable for the wires if you want a crisp, modern finish.
In late autumn (and certainly if you can before Christmas) plant the hornbeams, setting them 2.5m apart and orientating them so that any likely looking side branches are set parallel to the wires, not pointing fore and aft. Stick a tall bamboo cane behind each tree, then tie the cane to the wires above and the tree to the cane. If there are already some likely-looking side branches growing in the right place and in the right direction, tie them to the parallel wires.
The following summer, tie in the leader as it develops and any side branches that appear in the right places. Rub out any young growth that is obviously not going to be useful (that will include all the growth pointing straight out from the hedge). In winter, check the trees again (and the ties – they mustn't be too tight) and cut out any unhelpful growth you missed in summer.
Continue to prune and tie in like this until the whole screen is covered with parallel lines of branches. When the leader reaches above the top, bend it over and make it one arm of the last wire (and hope you get a sprout to cover the other side before too long). In subsequent years the main pruning and training will be easier to carry out in winter when you can see what you are doing, but the hedge will also need clipping to shape in summer. Rub out any shoots that appear on the clean, plain trunk below the leafy top. Within four years you should have a decent looking stilt hedge but if all this sounds too much of a fuss, buy ready-trained trees. Majestic Trees have them at £700-£1,000 each. That's a lot of money, yes, but the higher price buys you a superbly grown pleached hornbeam with a 2m trunk and a head of foliage already 2m high and wide. As you may gather from the DIY description above, you are paying for a lot of the nurseryman's time. Another advantage of buying the big, ready-trained trees is that you can do without the support structure. You still need to tie the branches of neighbouring trees to horizontal bamboo canes so that they stay straightish and mingle, and you still need, of course, to prune and clip them every year. They don't stand still – such a problem for the glitzy brigade who treat gardening as a slightly damper form of interior design.
The designer David Hicks used a variation on the stilt theme to great effect. First, he planted an ordinary hornbeam hedge. Then the stilts were planted in front of it. The hedge behind was clipped to the height at which the foliage of the stilt hedge started. When the whole thing filled out, you got a handsome impression of the stilt trunks rising like Roman columns against the foliage of the hedge tickling them from behind. The whole structure worked in two different vertical planes, one closer to you than the other. Very classy.
Hornbeam is undoubtedly the easiest tree to use for pleaching but others can be used too. Lime is sometimes recommended and was Harold Nicholson's choice at Sissinghurst. In his diary (20 March 1932) he recorded that "the Hayters have dug the places for the limes" but he got the wrong kind, Tilia x europaea, which suckers. This eventually became such a problem that by 1976, the National Trust, which now owns Sissinghurst, had to replace them with T. platyphyllos. At Erddig in Clwyd, another National Trust property, T. x euchlora was used to make the two double rows of pleached lime that face each other across the central walk. They are used effectively, too, at Lytes Cary in Somerset, where they make a short avenue at the approach to the house, and at Arley Hall in Cheshire.
Majestic Trees is at Chequers Meadow, Chequers Hill, Flamstead, St Albans, Herts AL3 8ET, 01582 843881, majestictrees.co.uk. The nursery is open Mon-Fri (8.30am-5pm) and Sat (10am-4pm). Send 6 x 1st class stamps for a catalogue