Pruning and Deadheading

The best time to prune buxus depends on the age of the plant, along with what it is being used for.

Young plants can be given ‘establishment pruning’ in May, whereby stems are cut back by a third to promote bushy growth. Further trimming can be carried out between then and August as required.

Mature plants are best trimmed annually in August once the growth has started to slow. Trimming earlier than this results in a flush of soft growth which, as well as looking less ‘sharp’ over winter, is more vulnerable to weather damage and disease.

While traditional advice was to prune box twice a year for optimum density and definition, it is now widely agreed that a looser form (with increased airflow through the plant) means better plant health and less vulnerability to pests and diseases. That said, buxus grown as topiary may need trimming twice (spring and late summer) to maintain its shape, particularly in the case of more intricate forms such as spirals or figures.

A useful thing to known when dealing with buxus is that it will regrow from old wood. Whether rejuvenating an overgrown specimen by cutting the whole lot back to 15-30 centimetres above ground level, or drastically reshaping an existing hedge/ ball/ topiary, your plant should respond with plenty of fresh, new growth. This sort of hard prune can be done in late spring, and is best followed immediately with a feed, water, and mulch (see below).

Whichever type of pruning you’re carrying out on your buxus, there are a few steps which will help limit the accidental spread of pests and diseases:

·         Always prune buxus on a dry day

·         Use clean tools, disinfected between each plant

·         Clear prunings away promptly (it can be a good idea to lay a sheet or some tarpaulin on the ground to catch them as you clip)

Watering

Like all woody plants, buxus establishes best when regularly watered during its first two growing seasons in the ground. After this it should be largely self-sufficient and may be left to its own devices in all but the hottest and driest weather.

In a container, water regularly throughout each growing season. Aim for consistently moist but not soggy compost. Allowing the top few centimetres to dry out before you give a deep, thorough soaking is best practice.

Feeding

It takes energy for plants to recover and regrow from trimming, and so it’s a good idea to get into the habit of feeding hedges and topiary shapes annually each spring. Apply a general purpose feed (blood, fish and bone is ideal), soak with water if the weather is dry, then cover with a mulch of well-rotted organic matter such as manure or garden compost. Don’t be tempted to skip the mulch – not only does it gradually release extra nutrients into the soil, but it also breaks down to improve soil structure, supresses weeds, and locks in moisture. Mulching really is the secret to healthy, sustainable plant growth.

Container-grown buxus relies even more on the gardener for nutrition. Get off to a flying start by making sure you use a good quality, loam-based compost with some slow-release fertiliser granules mixed in, then apply a monthly dose of balanced liquid feed throughout the growing season. Repotting every few years into fresh compost with slow-release granules is also beneficial, and when this is no longer feasible carry out a topdress each spring. Simply scrape away the top 5 centimetres of compost and replace with fresh. Finish with a good soak of water to settle the compost.

Cold Protection

Most species of buxus are hardy enough to withstand a UK winter without the need for additional protection.

B. balearica is a touch more tender than the rest and may need protection in a particularly harsh winter, particularly if grown in an exposed spot or a container. Cover with one of these handy fleece jackets and wrap the container in an insulating layer of bubblewrap, horticultural fleece, or hessian.

Pests and Diseases

Having been popular in UK gardens since the Roman times, buxus has, in recent years, sadly fallen victim to several serious problems, not least box blight and the box tree caterpillar.

Box blight is a fungal disease that causes bare patches, brown leaves, and dieback, and is especially prevalent in wet conditions.

The box tree caterpillar can completely defoliate entire plants in a matter of days. While relatively new to the UK, it has spread quickly, particularly in London and the surrounding areas.

The best form of defence is to grow healthy, thriving plants by following the advice above, and creating a balanced, thriving garden ecosystem by taking measures such as eliminating use of chemicals, providing food and habitat for wildlife, and growing a wide range of plants.

Quarantine any newly bought buxus plants for at least four weeks, keeping them away from the garden until you can be confident they are not harbouring blight.

If you spot signs of blight on existing plantings, it is important to act quickly to prevent spread. Dig out the affected plant entirely, along with the surrounding topsoil. Bag all waste up on the spot and dispose of off-site. Thoroughly clean and disinfect all tools, clothing, gloves, and shoes which are likely to be contaminated with blight spores. Moving forward, it’s best to avoid planting buxus in the same spot; opt instead for an alternative as suggested in our ‘Common Questions’ section below.

Box tree caterpillars can, where feasible, be removed by hand. For infestations which are less accessible or on a larger scale, a biological control known as ‘Fruit and Vegetable Protection’ may be effective. The RHS is keen to hear about all instances of this pest to help track its spread.