For most box garden hedges, multiply the length of the hedge in metres by 5 to calculate the number of hedging plants required. This corresponds to a spacing of 20cm (8 inches). So a 20 metre box hedge will need about 100 hedge plants, for example.
If it is to be a low hedge, say less than about 40cm high, then length in metres times 6 (16cm/6.5 inches spacing) is better. For tall hedges, over about 80cm high, length in metres x 4 (25cm, 10 inch spacing) is generally enough.
Either bare root or container grown hedging plants will succeed at any time of year. The main difference is that bare root hedging plants are cheaper to dispatch, take longer to establish, and need much more watering if planted in summer. We supply container grown hedging plants all the year round and bare root hedging plants from around mid-October to early April.
Purchasing larger box hedging plants will give a more immediate effect, but small hedging plants often establish more quickly than larger ones and tend to catch up before very long.
Box will grow in most situations. It is happy in acid or alkaline soils, in sand or clay, and will grow in very harsh dry places, or in deep shade. The only environment it is not suitable for is boggy or waterlogged ground. Box does grow wild in some very exposed places, but is not recommended as being particularly suited to windy sites.
Dig the ground over well to make a friable soil, and consider adding some organic material, such as peat or garden compost, if the soil is very sandy or very clayey.
With bare root box hedging plants, it is best to plant the box hedging trees with the soil at about the same level as before they were dug up. You can add bone meal or fertiliser when planting, but the pot grown plants have controlled release fertiliser in the pots anyway.
Water in well after planting, and in hot dry weather during the first summer after planting. Box can stand very severe droughts when established. If the soil is very dry or short of plant nutrients, then the leaves may temporarily become coppery-green coloured. Once the plant has enough water and nutrients, the leaves will turn green again.
Once the plant is established, buxus sempervirens will grow about 6 inches a year under reasonable growing conditions. In deep shade, very poor soil and very exposed sites, the growth rate is lower.
Clipped box hedges can be very old. For example some box hedges planted in the seventeenth century and clipped to about 35cm still look good with the original plants. Clipped box hedges can be anything up to about 3 metres tall.
In old box trees the growth rate eventually reduces and a one to two hundred year old box tree may be around 5-10 metres tall.
Most of the named varieties of buxus sempervirens, and the other species of buxus grow rather more slowly than buxus sempervirens.
It is best to keep trimming to a minimum until the hedge is close to the desired height. This will enable the plants to put on as much growth as possible. The trees will 'fill out' naturally without being stopped, and the lower branches will eventually touch the ground.
Once the plants are close to the planned height of the box hedge, cut the tops back to a few inches below the ultimate level. This is best done around mid-summer. Then trim to shape in August or September each year.
After a few years the clipped surfaces can become crowded, especially on the top of the hedge. This reduces the ventilation around the shoots. So it is a good idea to thin out some of the growing shoots every few years, by cutting out some of the main stems about 6-12 inches below the clipped surface of the hedge. The remaining branches will spread out to cover any gaps, while allowing more light and air into the hedge. The exact quantity of shoots to remove is found by trial and error.