After they are planted, pruning hedges is a very important part of their maintenance. Almost every hedge plant needs to be pruned every once in a while, in order to keep them from growing out of control. There are plants, almost exclusively deciduous hedging plants, that do not necessarily need to be pruned at all, but even those will profit from having diseased or dead branches removed on a regular basis. As a general rule, the more often you trim your hedge, the more formal it will look. The growth habit of a plant is a very important factor in its pruning requirements as well though, as a fast-growing hedge plant will lose its shape more quickly than a slow-growing variety.
When to Prune your Hedge
In line with the formal or informal appearance of a hedge, evergreen hedge plants usually need to be pruned more often, as they are generally used to grow a formal screening hedge, particularly conifers, like the yew, the thuja or the exceptionally fast-growing Leyland cypress. Deciduous species are often planted because they flower and look a little “wilder”. The latter group is often trimmed directly after flowering, while a formal hedge usually has its flowers removed in order to keep its shape clearly defined.
Avoid pruning on hot summer days or very cold days in order to prevent frost damage or burning leaves. Most hedge plants are pruned in September, but if a plant needs to be cut back twice a year, another pruning session in May is required. Also, make sure you use the proper tools. Garden shears are excellent for details, long-armed shears are perfect for cutting through thick branches and chainsaws can be effective for rough trimming.
Some hedge plants, especially the fast-growing varieties, have a tendency to become overgrown. This is not always disastrous, as some plants can easily be rejuvenated by cutting them back to old wood. The common yew is a well-known example of this. Not every plant generates new growth from old wood, however, in which case a hedge cannot be renovated without damaging the plants. This situation can easily be avoided by pruning your hedge whenever it needs to be pruned. The vigorous Leyland cypress and the slower-growing, but similar-looking Lawson cypress are plants that do not tolerate such hard pruning and therefore need to be kept in check by trimming them at least twice a year.
If you have topiary ambitions, keep in mind that keeping your specimen in shape is as much a part of the art as cutting it into that shape in the first place. This means that you need to trim your shaped box or Japanese holly at least four times each year, despite working with slow-growing plants. This will keep your works of topiary neatly defined. Experienced topiary artists use hedge shears for the rough shapes and sheep shears for the details.