Common holly (Ilex aquifolium) is an evergreen tree or shrub, recognized by the characteristic shape of its leaves and bright red berries. Its natural habitat is understories of oak and beech forests. Common holly is widely used in landscaping in temperate regions. Thick crown and prickly leaves make this plant excellent for hedges.
I. Appearance and CharacteristicsÂ
Ilex aquifolium, the holly, common holly, English holly, European holly, or occasionally Christmas holly, is a species of flowering plant in the family Aquifoliaceae, native to western and southern Europe, northwest Africa, and southwest Asia. It is regarded as the type species of the genus Ilex, which by association is also called “holly”. It is an evergreen tree or shrub found, for example, in shady areas of forests of oak and in beech hedges. In the British Isles it is one of very few native hardwood evergreen trees. It has a great capacity to adapt to different conditions and is a pioneer species that repopulates the margins of forests or clearcuts.
Ilex aquifolium grows to 10–25 m (33–82 ft) tall with a woody stem as wide as 40–80 cm (16–31 in), rarely 100 cm (39 in) or more, in diameter. The leaves are 5–12 cm long and 2–6 cm broad; they are evergreen, lasting about five years, and are dark green on the upper surface and lighter on the underside, oval, leathery, shiny, and about 5 to 9 cm long. In the young and in the lower limbs of mature trees, the leaves have three to five sharp spines on each side, pointing alternately upward and downward, while leaves of the upper branches in mature trees lack spines.
The flowers are white, four-lobed, and pollinated by bees. Holly is dioecious, meaning that there are male plants and female plants. The sex cannot be determined until the plants begin flowering, usually between 4 and 12 years of age. In male specimens, the flowers are yellowish and appear in axillary groups. In the female, flowers are isolated or in groups of three and are small and white or slightly pink, and consist of four petals and four sepals partially fused at the base.
The fruit only appears on female plants, which require male plants nearby to fertilise them. The fruit is a drupe (stone fruit), about 6–10 mm in diameter, a bright red or bright yellow, which matures around October or November; at this time they are very bitter due to the ilicin content and so are rarely eaten until late winter after frost has made them softer and more palatable. They are eaten by rodents, birds and larger herbivores. Each fruit contains 3 to 4 seeds which do not germinate until the second or third spring.
Holly berries contain alkaloids, theobromine, saponins, caffeic acid, and a yellow pigment, ilixanthin. The berries are generally regarded as toxic to humans. Accidental consumption may occur by children or pets attracted to the bright red berries. The berries are emetic, possibly due to the compound ilicin.
II. How to Grow and Care
Sunlight
Common holly requires an environment with bright and soft light to grow. It grows well in shady places, sheltered on one side, and even in direct sunlight. Mature plants have higher fruit growth rates in places with good light. Young plants, on the other hand, need a shady place (shade cloth can be used) in summer to avoid direct sunlight and prevent sunburn.
Common holly kept indoors should be placed in sunny rooms, about 50 to 100 cm from the window. Do not place the plant in an environment where light is completely blocked. After extended periods of insufficient light, the plant’s photosynthetic rate will decrease. This will slow down the growth rate possibly to zero, cause thin and weak leaves, and decrease the flowering and fruiting rate.
Watering
English holly is a fairly drought-tolerant shrub, but it prefers moist (not waterlogged) conditions in the warmer months. It should be kept drier during the winter.
Soil
Common holly likes acidic soil with a pH value of 5-6. In neutral or alkaline soil, its leaves tend to yellow and the plant may even die. It requires humid culture media that retain water and are rich in organic matter. Humus soil with an appropriate amount of coarse sand or perlite added will increase soil permeability. A formula for the culture medium, for example, could be 1/2 leaf mold + 1/4 coarse sand or perlite + 1/4 decomposed bark.
Before putting it into the pot, the medium should be soaked in a carbendazim solution to kill any bacteria and insect eggs. Some ceramsites can be put at the bottom of the pot to improve drainage and avoid water accumulation caused by excessive daily watering. Change the soil every two years.
Fertilizing
Common holly does not require much fertilizer. Apply some fertilizer during the growing season to promote luxuriant branches and glossy leaves. Apply thin fertilizer once in early spring and once in early autumn. Compound fertilizer mainly composed of nitrogen fertilizer can make the leaves brighter and bigger.
Stop fertilizing when the temperature is higher than 30 ℃ in summer to prevent root damage. Insufficient fertilization can cause thin and weak plants, sparse fruits, and thin and dull leaves. Large but dull leaves may be caused by over-fertilization and signal that fertilization should be stopped immediately.
Planting Instructions
Thought its red fruits are a Christmas symbol, it is generally best to plant common holly in spring. Large seedlings over 2 years old are preferred for planting. plants should be spaced about 1 m apart and there should be about 1 to 1.2 m between rows. Compacting the soil and watering after planting will allow the roots to be in closer contact with the soil. It should be noted that common holly is dioecious, so it requires both female and male plants present to produce fruits. Successful pollination only happens when plants are spaced no more than 9 m apart. One male plant can pollinate 6-10 female plants.
Pruning
Common holly flowers and fruits only grow on new branches, so the plant needs to be pruned to promote the germination of new branches. It’s best to prune before early spring, ideally during winter. In addition to promptly cutting off old, yellow, dried, and diseased leaves, one-third of the old branches should be cut off from the base every year. This promotes vertical growth, flowering, and fruiting. After winter pruning in cold areas where it snows, the remaining branches can be bundled with ropes to avoid damage caused by snow or ice on the branches.
Propagation
Propagating from cuttings or growing from seeds isn’t a quick process with English holly—cuttings take about 2 years to root, and seeds take 2 to 3 years to germinate. It’s much more practical to purchase additional plants.
Potting and RepottingÂ
English holly will generally be too large for containers at full, mature size. But, because it’s slow-growing, a young shrub can be contained in a container for several years before transplanting is necessary.
Be aware that the transplanting process can result in the shrub losing its leaves. New leaves should emerge the following spring.
Plants kept in containers are more likely to dry out, so make sure to keep the soil moist (not drenched).
Overwintering
English holly is cold tolerant and doesn’t require special care to survive the winter. It benefits from the period of cold and will fare better outdoors than indoors.
Pests and Diseases
Holly is hardy and not very susceptible to pests or diseases. However, the following issues may affect a holly shrub, especially if it is grown in conditions that compromise its resistance, such as overly wet soil: root rot, anthracnose, tar spot, leaf blight, and bot canker. These fungal diseases can be treated by reducing water input, amending the soil to improve drainage, and applying fungicide if necessary.
III. Uses and BenefitsÂ
- Ornamental uses
Ilex aquifolium is widely grown in parks and gardens in temperate regions. Hollies are often used for hedges; the spiny leaves make them difficult to penetrate, and they take well to pruning and shaping.
- Culinary uses
The leaves of yerba mate, also in the genus Ilex, are used to make a caffeinated beverage called mate or Paraguayan tea.
- Other uses
Between the thirteenth and eighteenth centuries, before the introduction of turnips, Ilex aquifolium was cultivated for use as winter fodder for cattle and sheep. Less spiny varieties of holly were preferred, and in practice the leaves growing near the top of the tree have far fewer spines, making them more suitable for fodder.
Ilex aquifolium was once among the traditional woods for Great Highland bagpipes before tastes turned to imported dense tropical woods such as cocuswood, ebony, and African blackwood.
IV. Harvesting and Storage
In suitable growth conditions, common holly blooms and bears fruits once a year. The fruits appear in fall and winter, and can be appreciated for a long time before picking. Without birds in the yard, the fruits often persist into the next spring. The vase life of fruit-bearing branches after picking is about 20-40 days.
Use sharp garden shears when picking and cut the base of branches at a 45-degree angle, or make the cut into a cross, to increase the water absorption area. Quickly put the cutting in a vase with clean water to avoid water loss. The fruits of Ilex verticillata can also be air-dried since they tend to not drop from the branches. Their colors will change from bright red to deep red, providing good ornamental value.