Japanese winterberry

Identification and origin

Ilex serrata belongs to the Aquifoliaceae, the holly family. Unlike English holly, it is a deciduous shrub. Its native range covers central and southern Japan and southeastern China as far as Sichuan, where it grows along forest edges, in thickets and on mountain slopes. It has been introduced to Korea. In Japan it is called umemodoki.

In China the shrub grows 3.5–10 ft tall. In cultivation it can reach 15 ft, with an upright to arching habit and spreading branches. Its young shoots, angled and finely downy, form an almost horizontal zigzag; they turn from light brown to dark gray, and the bark is gray.

• Leaves: alternate, thin, elliptic and pointed, 1–4 in long and 0–2 in wide, with margins lined with small, tightly set teeth, hence the species name. Tinged bronze-red as they unfold, they turn medium green and drop without notable fall color.
• Flowers: tiny, in small clusters in the leaf axils in spring; the open, flat corolla is about 0 in across. They are inconspicuous and pale pink.
• Fruit: round red berries about 0 in across, ripening in fall. They hang on the bare stems for a long time and keep their color. There are forms with white fruit (f. leucocarpa) and yellow fruit (f. xanthocarpa).

The species is dioecious: each plant bears either male or female flowers. Only female plants produce berries, and only if a male plant blooms nearby at the same time; bees do the pollinating. An evergreen holly cannot pollinate a deciduous one.

Japanese winterberry looks very much like the North American winterberry (Ilex verticillata), whose fruit is slightly larger and brighter.

Light

Japanese winterberry likes a sunny position. It tolerates part shade, but it flowers and fruits best in sun: several hours of direct sun a day suit it well. In hot climates, light shade during the hottest hours of summer protects it.

Watering

In the ground it prefers moist soil and even tolerates wet soil, but it should neither sit in standing water nor dry out completely. After planting, water during dry spells in spring and summer for the first two years, until the roots are well established.

In a container, don’t follow a calendar: water thoroughly as soon as the surface of the mix starts to dry, until water runs out of the bottom. Water needs rise sharply during active growth and in hot weather, and drop considerably in winter, when the shrub is leafless. Never let the root ball dry out entirely.

Potting mix

Like other deciduous hollies, it prefers neutral to acidic, well-drained soil rich in organic matter, whether clay or loam. Alkaline soil makes holly leaves turn yellow. In the ground, an organic mulch in spring is enough, with no special fertilizer unless deficiency signs appear. In a container, choose a free-draining mix that still holds some moisture; for bonsai, a blend of akadama, pumice and a little humus works well.

Temperature

Japanese winterberry is a hardy shrub, suited to USDA zones 5 through 8a. It tolerates frost, but most deciduous hollies do poorly where the climate is both very hot and humid. In a container, the roots are far more exposed than in the ground: protect the root ball when temperatures fall below 23 °F, for example by burying the pot or sheltering it against a wall. It needs a real cold winter rest and is not grown indoors.

Repotting

Repot in spring, when the buds begin to swell, never in midsummer. A young container plant is repotted about every two years, with moderate root pruning; an older one can wait longer. In the ground, plant it in loosened soil and, if possible, place a male plant not far from the female plants: one male can pollinate several females within a radius of 65.5–164 ft.

Pruning

Deciduous hollies need little pruning: a light cleanup in winter, while the branches are bare, is enough to remove dead or badly placed wood. If needed, the plant can be reduced by up to one third in a single year. On a bonsai, new shoots are cut back to two leaves once they have formed four, but the tree is never stripped of all its foliage, which it needs to ripen its fruit.

Propagation

• Seed: collect ripe berries in fall, extract the seeds by hand and sow them fresh outdoors or in a cold frame so they go through winter cold. Stored seed needs about three months in the refrigerator, in a moist medium, before sowing. Germination is slow and can take two to three years.
• Cuttings: these remain tricky with hollies. Take semi-ripe cuttings from late summer to early fall, or hardwood cuttings from mid-fall to late winter.
• Layering: the easiest and most reliable method for hollies, although rooting can take two years.

Common problems

Hollies are generally tough. In spring, young shoots sometimes attract aphids; a targeted treatment controls them easily. Spider mites and nematodes turn up occasionally. Scale insects can also appear, and their honeydew encourages sooty mold, a black coating on the leaves.

A shrub without berries is not necessarily sick: it could be a male plant, or a female with no male in bloom nearby at the same time. Birds love the berries and eat them as soon as they redden; netting protects the crop. Yellow leaves can point to soil that is too alkaline, but the same symptom can have several causes: check watering and drainage as well.

Toxicity

Hollies contain saponins. In dogs, cats and horses, eating the leaves or berries mainly causes nausea, vomiting, diarrhea and depression; toxicity is considered low. In people, the fruit is the main concern: eating it can cause vomiting and diarrhea, with low severity. Contact with the plant does not irritate the skin. Keep the berries out of reach of children and pets.