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Boxwood

Folkert Siemens Folkert SiemensKathrin Auer Kathrin Auer

Hardly any plant has influenced the gardening culture the way boxwood has. Even if it is diseased or infested with pests — it pays to fight for it!

Origin

The name of the genus boxwood (Buxus) probably comes from the Greek word "pyxis", which means "box". Cans and other small containers were produced in olden days from the bright, strong wood with small pores. The genus gives its name to the boxwood family (Buxaceae), which includes around 70 species worldwide. They are found all over Central Europe and Africa till East Asia in the northern hemisphere. Around 20 species are found in Central America. Only the common box (Buxus sempervirens) is native to Central Europe. There are also relict occurrences in southwest Germany on warm, sunny mountain slopes on lime-rich soils.

Apart from the Common box, the Japanese box and Littleleaf box (Buxus microphylla) are important from a gardening perspective. It, in fact, originates from Korea, however, it has been cultivated in Japan since centuries. In general, the species is undemanding when it comes to care, and grows on all soils, as long as they are porous and not bone-dry or water-logged. Very barren, sandy soil with a low pH is not ideal either. If possible, the location should be a little sheltered and not in full sun. However, the shrub is very resilient and can withstand temporary drought, as its fine, fibrous roots penetrate very deep into the soil and are also spread out widely just below the surface.

Buxus sempervirens var. arborescens (left) and Buxus microphylla (right)

Appearance and Growth

Both boxwood varieties look quite similar. The native common boxwood grows somewhat stronger and can reach heights of 16.4 to 19.68 feet with age. The leaves are conspicuously small, depending on the species and variety, they can be round, long, alternately arranged and evergreen. The shoots have fine long bark strips and therefore appear slightly rectangular. New branches have a green bark, the older branches are light gray. The branching is quite dense and the crown looks compact and round even without any trimming. The inconspicuous, yellow-green flower clusters are visible in the leaf axils from end of March. They are full of nectar and therefore, an important food source for the bees. The greenish capsule fruits ripen in September.

Location and Soil

The boxwood grows best on chalky, loamy soils. If you have soil that’s purely sandy, you should include plenty of ripe compost when you plant the boxwood. The soil should be permeable and moist but not waterlogged. When it comes to light conditions, the boxwood is very tolerant. It tolerates shade and can also survive fi planted near the roots of trees. Hot locations which get a lot of sunshine, for example in front of a south wall, are a challenge. In such locations, the leaves get damaged fairly quickly.

Box tree
Box trees like nutrient-rich soil

Planting boxwood

The boxwood as edging is usually sold in pots, sometimes bare-rooted in small bundles. Best time to plant is in spring. Place the shrubs with the roots in a bucket of water, then loosen the soil thoroughly and work in if necessary. Then mark the position of the flower bed edge with a planting cord and lay out the plants. When planting,a hedge or border, the boxwood should be placed relatively close. For plants that are 3.93 to 5.90 inches high, you will need approximately 32.8 plants for every foot. For higher bushes 15 to 18 boxwoods suffice. If the soil is loose, it is best to use a planting trowel. Finally, water the new edging and cut it back to two thirds with the hedge trimmer. The border should be kept moist until it has grown in and fertilize at the beginning of June.

Boxwood care

Boxwood is more drought-tolerant than generally assumed, but as a container plant it needs water every day in warm, dry weather. Occasionally sprinkle water over the plants during longer hot periods, so as to remove dust deposits from the plants. Ensure that the root ball is does not dry out during the winter months. Potted plants also need regular nutrients from mid-April to early August - ideally liquid boxwood fertilizer, which must be administered once a week by mixing it in the water. A typical symptom of nitrogen deficiency is reddish to bronze-colored leaf discoloration.

Pruning the boxwood

The boxwood can tolerate any type of trimming. In principle: Better if it is done more often. Vigorously growing varieties only become really dense if you cut more than once a year. Topiary plants should be cut one to five times a year, depending on the level of detail in the figures. The pruning season is limited to the main growing season from April to September. Pruning before of after this season is not required, as the plants hardly grow during this period. Out of shape hedges, borders and figures can be easily cut back to the basic structure from the end of March. Cutting back into perennial wood is no problem.

Only prune your boxwood in summer when the sky is overcast. There is a danger of leaf burning in full sun, since the leaves in the inner portion of the crown are not accustomed to intense sunlight. In case of doubt, shade the plant for two to three days with a fleece. And: If you prune your boxwood frequently, then you must increase the water and nutrients intake so that they can quickly replace the missing leaves. In early spring, ripe compost is distributed in the root area, which has previously been enriched with a handful of horn meal or horn pellets.

If you want to create a beautiful boxwood ballwithout tools, proceed as follows: First cut a horizontal "equator" and four vertical "longitudes" into the ball. When these tracks are evenly round, it is easy to shorten the remaining fields to the correct length. A good idea is to use a cardboard template: First measure the diameter of the box ball with a folding meter stick. Then attach a felt-tip pen to a cord that is almost half the length of the diameter of the boxwood ball. Fix the measured piece of string between your thumb and forefinger and hold it right at the edge of the cardboard. Then draw a semicircle from the top of the cardboard edge to the bottom. Finally, cut out the semicircle - and the template is ready. When cutting boxwood, place the template on the boxwood ball in several places and cut all branches down to the edge of the template. Tip: Specialized metal templates for cutting boxwood are also available in specialist shops.

Boxwood balls in tree park

Boxwood balls in the Arboretum Ellerhoop-Thiensen tree park

Cutting with cordless shrub shears is convenient, but it is usually not worth purchasing for two or three box balls. Beginners should first use mechanical shears to practice, as it is easy to end up cut too much with motorized devices. Special boxwood shears with short cutting edges are ideal for cutting simple shapes. It has to be very sharp so that the tough shoots can be easily cut and do not slip off when cutting. The classic blade shears are only suitable for shoots that are not too woody.

Overwintering or Winter Protection

Boxwood is hardy, but a bit sensitive to direct sunlight and ground frost. To prevent the leaves and shoots from suffering from so-called frost drought, you should overwinter container plants in a partially shaded place outdoors and cover the crown with winter protection fleece. As with all evergreen plants, the boxwood should only be watered in frost-free weather, even in winter. A "pot-in-pot solution" is recommended to protect the boxwood roots in winter: You put the plant including the pot in a much larger planter and fill the space in between with chopped tree bark (bark mulch). Both the inner pot and the planter are placed on two wooden blocks to prevent direct contact with the cold floor.

Boxwood in snow
Like all evergreens, the boxwood also suffers in cold winters

Shading nets can prevent the worst from happening with container plants, but that is hardly practical with long hedges and borders. To prevent frost damage, you should not plant the box in the blazing sun. You can also avoid damage by choosing the right variety - “Blue leaved box”, “Handsworthiensis” and “Little-leaf boxwood” are particularly hardy. Fertilizing in September with Patentkali (a special potash fertilizer also called potash magnesia, available in rural stores) promotes lignification and thus the frost hardiness of the shoots and leaves.

Where to plant the boxwood

Boxwood figures
For complex boxwood sculptures, you need vigorously growing varieties

Box trees are suitable for any type of topiary, even for very detailed figures. In cottage gardens, rose gardens and formal gardens, it is one of those plants that can confidently be called "indispensable". The European wild species (Buxus sempervirens) and fast-growing varieties such as ‘Handsworthiensis’ are also suitable for cut privacy hedges up to about 6.56 feet in height. Shaping of the boxwood is optional: You can also let the competitive, evergreen shrub grow freely and, for example, integrate it into a wild wood hedge or use it as an understory plant for taller trees. As a topiary plant, it is also suitable for larger planters on the balcony and patio. A word of caution: The boxwood is poisonous and could prove harmful for housepets and children.

Important Species and Varieties

Not all boxwood is the same because there are clear differences between the different types of boxwood in terms of vigor, leaf shape and leaf color. While it is best to use slow-growing varieties such as “Suffruticosa” or the frost-hardier variety “Blue leaf boxwood” for borders, the wild type Buxus sempervirens or vigorously growing varieties such as “Rotundifolia” and “Handsworthiensis” are suitable for higher hedges. Same is applicable for cut figures: For small balls, use “Suffruticosa” or “Green Gem”, for larger sculptures, use the suitable taller varieties. Variegated-leaved varieties such as ‘Elegantissima’ are relatively sensitive to frost and therefore always need a protected location.

Buxus sempervirens “Elegantissima”

The variegated Buxus sempervirens “Elegantissima” needs a protected location

Propagating the boxwood

Boxwood is propagated through cuttings. It is not difficult, but requires a lot of patience: It takes about half a year for the first roots to form. Those who wish to have big plants, use cuttings that are already 7.87 to 11.81 inches tall. These cuttings take root very well: You simply tear it off from the parent plant in July / August and remove the protruding strip of bark at the split with a sharp knife. Then all shoots are shortened by about a third. The cuttings do not necessarily need a foil cover. You put them in a partially shaded, sheltered place directly in loose, humus-rich and loamy garden soil. Professionals cover the flower bed with black foil before pinning. It suppresses weeds and prevents the soil from drying out.

The following method is also very efficient for borders that are to be strongly rejuvenates: You ridge the shoot base with humus-rich soil and remove it after a few months. The shoots have now re-rooted at the base - they are cut off in autumn and planted in the desired location. The existing edging springs out of the old wood again in spring.

Diseases and Pests

Nowadays, in particular, diseases and pests have severely affected the popular wood. It is often attacked by, shoot death (Cylindrocladium) and by the boxwood moth (Cydalima perspectalis, a parasitic butterfly species from East Asia. The green-yellow caterpillars not only eat the leaves, but also the soft bark, so that entire shoots often die. It can be combated by timely and repeated sprayings with a biological preparation with a Bacillus thuringiensis base. The damage caused by boxwood shoot death is characterized by dark brown spots on the leaves, which quickly become larger and coalesce together. At the same time, numerous small white spore beds form on the underside of the leaves. Various experts have observed that the garden forms of the small-leaved boxwood (Buxus microphylla) are quite resistant to the fungus that causes shoot death. According to some experts, the application of algae lime should also prevent the fungus from spreading. The box tree can hardly be replaced in landscape designing. Plants with a similar range of uses include the slow-growing garden forms of the yew (Taxus).

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