Japanese Holly (Ilex crenata)

Ilex crenata, also referred to as Japanese Holly, offers a similar aesthetic to Box hedging, due to the small, glossy green foliage and dense habit. Ilex crenata is perfect to use as a low-hedging option for your garden. It’s aesthetically pleasing to the eye and provides year-round interest. Japanese Holly hedging has many gardening benefits such as its robust qualities and low maintenance needs.

I. Appearance and Characteristics

Ilex crenata, also known as Japanese holly or box-leaved holly, is a species of flowering plant in the family Aquifoliaceae, native to eastern China, Japan, Korea, Taiwan, and Sakhalin.

It is an evergreen shrub or small tree growing to a height of 3–5 m (rarely 10 m) tall, with a trunk diameter up to 20 cm. The leaves are glossy dark green, small, 10–30 mm long and 10–17 mm broad, with a crenate (wavy) margin, sometimes spiny. The plants are dioecious (having separate male and female plants), with white, four-lobed flowers. The fruit is a black drupe (stone fruit) 5 mm diameter, containing four seeds. It grows well in acidic soil, between a pH of 3.7 and 6.0.

Common name	Box Leaved Holly, Box-leaved Holly, Japanese Holly
Botanical name	Ilex crenata
Family	Aquifoliaceae
Species	crenata
Origin	East Nepal to Temperate East Asia, Japan and Korea
Life cycle	Woody
Plant type	Perennial
Hardiness zone	5, 6, 7, 8
Sunlight	Full Sun
Maintenance	Medium
Soil condition	Clay
Soil ph	Acid
Drainage	Well-Drained
Growth rate	Slow
Spacing	3 ft. – 6 ft.
Harvest time	Fall
Flowering period	Spring
Height	5 ft. – 10 ft.
Width	5 ft. – 10 ft.
Flower color	Green
Leaf color	Green
Fruit color	Black
Stem color	Gold, Yellow
Fruit type	Drupe
Fruit benefit	Showy
Leaf benefit	Good Cut
Flower benefit	Fragrant
Garden style	Cottage Garden
Uses	Woodland

II. How to Grow and Care

Sunlight

Japanese holly grows best in full sun to partial shade. In warmer climates, it will appreciate some shade from the harsh afternoon sun. But in cooler climates, it typically should have full sun or at least six hours of direct sunlight on most days to grow its best. Too little light will result in slower growth and less dense branching.

Temperature and Humidity

Japanese holly prefers a temperate climate and doesn’t do well in extreme temperatures, both hot and cold. It is best to plant your shrub in a spot that is protected from harsh winds, which can damage the foliage during the winter. The shrub also tends to struggle in areas with high humidity and instead prefers average humidity levels

Watering

Japanese holly plants like a moderate amount of soil moisture. Keep young shrubs in evenly moist but not soggy soil to help them establish their root systems. Mature shrubs have some drought tolerance, and they also can tolerate occasional flooding. However, sitting for too long in wet soil can cause the foliage to turn a pale green and ultimately rot the roots, killing the plant.5 Water whenever you can stick your finger into the soil and it feels dry a couple of inches down. To help maintain adequate soil moisture and keep the roots cool, add a two to four-inch layer of mulch around the shrub.

Soil

This shrub can tolerate a variety of soil types, from sandy and rocky soil to clay soil. Ideally, it should be planted in loose, loamy soil that has good drainage. It prefers a slightly acidic soil pH.

Fertilizing

Japanese 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

Though its red fruits are a Christmas symbol, it is generally best to plant Japanese 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 Japanese 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

Japanese holly shrubs don’t need much pruning. But they can be cut back as needed to maintain the desired shape. They generally can handle light pruning at any point in the spring to early fall, though any substantial pruning should be performed in the early spring before new growth starts. Avoid pruning roughly two months before the projected first frost in the fall, as pruning can encourage tender new growth that the frost will damage. Remove any dead, damaged, or diseased branches as you spot them.

To shape your Japanese holly into a hedge or topiary, lightly prune it several times during the growing season. Don’t severely prune it into your desired shape all at once. However, if you have an old shrub that needs rejuvenating, cut it back in the late winter to roughly six to 12 inches off the ground. This will encourage healthy new branches to grow and reform the shrub.

Propagation

During the dormant season, Japanese holly can be propagated from hardwood cuttings:

• Using a sharp knife or pruners. cut a cane right below one of the bud unions (the small bumps where the leaf meets the stem). Then remove about three-quarters of an inch of the cutting above another bud union so you end up with a cutting about six inches in length. Remove all but two sets of leaves.
• Dip the bottom end of the cutting in rooting hormone.
• Prepare a location where the shrub will receive the necessary full or partial sun exposure. Work coarse sand into the soil and plant the cutting about one inch deep.
• If there is no rain or snow, water the cutting frequently to keep it moist. In the spring, the cutting should develop new growth, which indicates that it has rooted. Let it grow in the same location or transplant it to another suitable location.

Potting and Repotting

Dwarf varieties of Japanese holly are suitable for container growing. Choose a container that is at least 8 inches wider than the root ball of the plant to give the shrub room to grow for the next two to three years before repotting the plant to a bigger container. When repotting a Japanese holly, it’s best to do so in the spring and do a light root pruning, as well.

Terracotta is an ideal pot material because it lets excess moisture evaporate and it is heavy enough so the container does not topple over easily. Fill it with a well-draining potting mix and make sure the container has large drainage holes.

Overwintering

Japanese hollies are hardy to USDA zone 5 and, generally, need no winter protection when planted in a suitable location sheltered from strong winds. But they benefit from several inches of mulch over the roots to protect them from the freeze-thaw cycle. The mulch should be spread as wide as the reach of the branches.

The roots of Japanese hollies in containers are susceptible to root damage from winter cold and should be winterized with an insulating silo.

Pests and Diseases

Japanese holly can be affected by the holly leaf miner in the late spring. The female leaf miner will suck the fluid out of the plant’s leaves. You can tell when a female has deposited eggs on the plant because the underside of the leaves will be riddled with small green blisters. The damage to the leaves will show up as brown, yellowish, or reddish lines. Other pests include scale, whiteflies, and spider mites. Address these pests with neem oil, a natural insecticide.

During wet seasons, the plant is prone to root rot, which can be identified if you spot yellowing leaves. You may have to replant the holly in better-draining soil. Stem canker is a fungal disease that can afflict the Japanese holly. If you see reddish lesions on lower stems, this could be an early symptom. If you spot patches of dead plants, it is usually a late symptom of stem canker. Stem canker is potentially managed with fungicides.

A common issue is yellowing leaves. This is usually a sign that the soil is too alkaline, which causes iron deficiency in the plant, although there might be sufficient iron in the soil. Hollies can only absorb iron when the soil is slightly acidic, To remedy this, feed it an acid-loving tree-and-shrub fertilizer and follow the label instructions.

III. Uses and Benefits

Ilex crenata is ideal for low-hedging and also works well as privacy screen and windbreak for your outdoor space whilst providing year-round interest. The compact and versatile habit of Japanese Holly makes a fantastic choice for topiary shapes.

Japanese Holly hedging is very versatile, it can be grown alone for a neat evergreen garden feature, or, when planted alongside small bulbs and plants, Japanese Holly can create a cottage-style garden or informal aesthetic.

IV. Harvesting and Storage

In suitable growth conditions, Japanese 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.

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