The ideal site for a box plant is in a deep fertile well drained soil in a sheltered partially shaded site in a temperate climate. However, it is a very adaptable plant, and will grow well in almost any situation except a permanently water-logged soil. Hence, it is also very well suited to growing in containers.
Buxus plants will thrive in any reasonable garden soil with adequate drainage. Box prefers lime based ground, and wild buxus sempervirens plants will colonize the limestone bands in hilly areas with different rock layers. However, when planted in acid soil, it also grows very well.
In a container, box will grow in any reasonable garden compost with adequate nutrients (see 'Food' below). Peat, or peat plus loam, based composts generally produce better results than garden soil.
Box succeeds in full sun or shade. Buxus sempervirens often occurs wild as an under-shrub in mature deciduous woods. But it will grow faster in relatively high light levels.
Box grows wild in Mediterranean garrigue conditions, so can obviously withstand severe drought once the plants are established (see 'water' below). Moist, well-drained conditions produce maximum growth. It will not grow in permanently water-logged soil.
Temperature and Shelter
Box can stand hard frosts, hot sun and strong winds when established in the ground. Newly planted specimens, especially large ones, require watering in hot, dry and/or windy weather for a year or two at least, until they are established.
Feeding your box plant is essential for healthy growth when it is kept in a container, and something you may wish to do, but is not strictly necessary, if your topiary is planted in the ground.
Slow or controlled release fertilizer granules are the most convenient method of feeding, as they only need be applied infrequently. They should be placed in a hole in the top of the compost, or added with a top dressing of fresh compost. The frequency of application depends on the life of the granules, which varies from about 3 to 15 months. Otherwise ordinary fertilizer granules or liquid feed can be used as required during the growing season.
If a box plant is short of nutrients, it will only grow very slowly. The leaves will tend to become coppery brown, or will develop cream or yellow tips and margins. Once good growing conditions are restored, the leaves will become uniform green again within a few weeks.
Most topiary plants will have been grown in the open ground, and then lifted with a root-ball of soil attached to the roots and placed in a container a relatively short time before being sold. So, the plant will have lost a significant proportion of its roots, and will be susceptible to drying out for at least a year or two after planting.
It is especially important to water large topiary plants in sunny and/or windy sites and during hot summer weather during the first year or two after planting. Once the plants have become established in their new site, they will require far less watering, and after a few years they should be able to withstand any UK drought easily.
Box naturally grows between about the months of April and June inclusive. So around mid-Summer is a good time to trim the new growth. The new growth can be cut easily with scissors or shears. If the plant is in a container, then placing the container on a surface such as a table top, where it can be rotated, can make accurate trimming relatively easy.
If you would like to increase the size of the plant, then you can leave an inch or two of the new growth each time the plant is trimmed. In this way, the size can be increased while maintaining the thick bushy appearance of the plant. A second trimming around August may be required.
If the foliage becomes too thick, it is a good idea to periodically thin out the growth by removing some branches around 6-12 inches long. The neighbouring branches will cover the hole, and this pruning will allow more light and air into the centre of the plant. This thinning of the plant is especially useful with dense plants which are susceptible to fungus attacks in certain situations, for example buxus sempervirens 'Suffruticosa'. The better air circulation is said to often cure any fungal attacks of the foliage and/or stems.
Any plant in a container has a smaller root ball than the same sized plant growing in the ground. Box grows relatively well in containers compared to most other plants, but will need more watering and feeding than a plant in the ground, especially in exposed sites.
It is desirable to pot the plant on into a larger container at intervals of about two years, to allow the root ball to increase in size as the plant grows. If this is not possible, then top-dressing with a layer of fresh compost will certainly help. Also, it may be worth taking the plant out of the pot, and removing some of the roots and then putting it back in the container with some fresh compost may help rejuvenate your topiary plant.
Generally speaking, the solution to any problems usually lies in making sure the plant has satisfactory growing conditions, as outlined above; removing any dead or diseased growth; and possibly in spraying with a fungicide and/or insecticide. Normally making sure the plant has food, water, light, air and shelter, possibly including moving it to a different site, will cure any problems.
Not many things eat box. Rabbits and deer will only consume buxus if no other food is available. In practice this means that box is not eaten by large animals.
Sometimes small insects attack the leaves. These may be leaf burrowing or scale forming creatures. These insects are best controlled by removing badly effected branches and/or spraying around May, when the leaves are soft and the insects are susceptible to spraying.
There are various, generally fungus related, diseases that can affect buxus plants, especially where the growing conditions are not ideal (eg too dry or water-logged soil, or too dense foliage).
The best way to control any of these diseases is generally to improve the growing conditions as much as possible (see above), remove any badly affected branches, and to spray with a fungicide if a fungus infection is a possibility (eg if the leaves are going brown or black, or falling off).
Box plant leaves will go a coppery brown colour if the plant is short of nutrients, or if it is exposed to very cold winds, or to prolonged frosty weather.
One of the commonest problems with box topiary in containers in the UK seems to be the leaves going brown or coppery after a few months to three years, because all the nutrients have been leached from the compost and no feed has ever been added to the pot. This difficulty is very easily rectified by adding some fertilizer (see Food above), and the brown leaves will become green again within a few weeks.
Brown leaves due to cold winds and/or hard frost are common in countries with colder winters than most of the UK (eg the mountainous and central parts of Europe and much of the USA). The leaves turn green again as the weather warms up in Spring.
Cream/Yellow Tipped/Edged Leaves
If a buxus plant is unhappy, it usually makes this known through the colour of its leaves. White, cream or yellow tips or borders to the leaves are a common sign of stress, especially in young recently transplanted plants and pot-bound older plants. The leaves will become uniform green again when the growing conditions improve or are improved.
When starting with a small un-trimmed box plant, the initial aim should be grow a bigger plant; then to make it approximately the right shape; and finally to mould the finished topiary shape.
If the plant is already close to the desired size, then it will need pruning to approximately the desired shape, which may well involve removing a large proportion of the branches. It should then be grown on and trimmed, in order to form the required shape.
A third variation is to start with an existing topiary shape, and then either grow and trim it to a larger shape (eg a larger box ball from a smaller one), or trim it to a different but similar shape (eg form a pyramid or column from a cone, or a cube from a ball and so on).
Balls and Cubes
Any box balls sold commercially will be several years old. If growing one from a young box plant, a roughly shaped ball can be formed more quickly than a thick bushy sphere suitable for retail sale. Plants which are naturally wide and bushy are obviously most suitable for growing into box balls, cubes and similar shapes.
A cut-out circle or semi-circle formed from cardboard or plywood can be useful in trimming an accurate sphere.
Where a plant seems too tall and leggy to form a sphere, this can often be corrected by planting it deeper, so that the width is about equal to the height.
More than one plant can be used to form a single topiary shape perhaps more quickly than from a single bush. This method is often used to form a cube by putting one plant near each corner of the cube.
Cones, Pyramids and Columns
Generally speaking, the method for forming these taller shapes is very similar to that for balls and cubes, although the plants are obviously grown into a taller and narrower shape.
Topiary spirals are generally formed from cones by 'marking out' a spiral on the cone and then trimming the shape back to the central trunk.
When selecting a cone to convert to a spiral it is important to make sure that the cone has a single central trunk with fairly horizontal branches, rather than a group of vertical trunks and branches, as is often the case.
Standards can be formed by selecting a box plant with a straight trunk already of the desired height, removing the lower branches, and trimming and growing the crown into a sphere. Alternatively, young plants can be 'drawn up' to make long stemmed trees (eg growing them close together); supporting the stem with a cane; and then 'stopping' the main shoot when it has reached the desired height and trimming the top to a ball shape. This process will take a number of years.
Box can be trimmed into almost any shape, either by carefully shaping a free-growing plant, or by planting a plant or plants in a wire netting frame and trimming any shoots that grow through the frame.