Winterberry (Ilex verticillata)

Black Alder, Common Winterberry, Winterberry, Winterberry Holly

Common winterberry (Ilex verticillata) is a berry species commonly grown in eastern gardens within the United States. Common winterberry is valued for its ability to grow in temperate climates and the colors it provides as an ornamental plant. The common winterberry is also called Michigan holly.

I. Appearance and Characteristics 

Ilex verticillata, the winterberry, is a species of holly native to eastern North America in the United States and southeast Canada, from Newfoundland west to Ontario and Minnesota, and south to Alabama.

Other names that have been used include black alder, Canada holly, coralberry, fever bush, Michigan holly, or winterberry holly.

The species occurs particularly in wetland habitats, but also on dry sand dunes and grassland. The berries are an important food resource for some species of bird, among them the American robin.

Ilex verticillata is a shrub growing to 1–5 m (3–16 ft) tall. It is one of a number of hollies which are deciduous, losing their leaves in the fall. In wet sites, it will spread to form a dense thicket, while in dry soil it remains a tight shrub. The leaves are glossy green, 3.5–9 cm (1+3⁄8–3+1⁄2 in) long, 1.5–3.5 cm (5⁄8–1+3⁄8 in) broad, with a serrated margin and an acute apex. The flowers are small, 5 mm (0.20 in) in diameter, with five to eight white petals.

The fruit is a globose red drupe 6–8 mm (0.24–0.31 in) in diameter, which often persists on the branches long into the winter, giving the plant its English name. Like most hollies, it is dioecious, with separate male and female plants; the proximity of at least one male plant is required to pollinize the females in order to bear fruit.

It is easy to grow, with very few diseases or pests. Although wet acidic soils are optimal, the winterberry will grow well in the average garden. Numerous cultivars are available, differing in size and shape of the plant and color of the berry. At least one male plant must be planted in proximity to one or more females for them to bear fruit. Because both females and males come in early- and late-flowering varieties, males must be selected to have the same timing as the females they are intended to pollinate.

II. How to Grow and Care

Sunlight

Common winterberry require 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 winterberry 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.

Temperature and Humidity

Winterberry has a good tolerance for all temperature and humidity conditions across its hardiness range, though it does not do well in conditions of prolonged dryness.

Watering

Common winterberry grows in humid environments and is not resistant to drought. Keep the soil moist during spring and summer. If rainfall is less than 2.5 cm per week when cultivated outdoors, manual watering is required. Water once a day and ensure that the soil around the root system is completely wet. Surplus water should drain away smoothly without accumulating. Spray mist during the day to increase air humidity, which is preferably kept at 70%-90%. After the fruiting period in winter is over, gradually reduce the watering frequency to once a week, and completely drench the soil only if it is completely dry.

It is best to water common winterberry in the morning and evening because the temperature around the root system tends to rise if it is done at noon, especially in summer. This will cause damage to the plant. Use rainwater and distilled water rather than tap water, which contains a large amount of calcium and magnesium mineral salts. Long-term use of tap water will cause salinization, hardening, and poor permeability of the soil as well as affect plant growth and ornamental effect. Inadequate or excessive water will both cause the leaves to turn yellow and shed.

Soil

This plant adapts to both light and heavy soils but performs best in acidic loam (pH range 5.5 to 6.5) with a good level of organic material. It does poorly in neutral to alkaline soil, which can cause fatal chlorosis (yellowing of the leaves). Feeding it with a fertilizer designed for acid-loving plants can help modify soil pH levels if a soil test reveals soil that is neutral or too alkaline.

Fertilizing

Common winterberry 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 winterberry 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 winterberry 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

Because the flowers (and resulting berries) appear on new growth, winterberry holly should be pruned to shape in early spring, just before new growth appears. Pruning is recommended because these shrubs not only grow tall, they also sucker profusely if not controlled. Remove up to (but no more than) 1/3 of the branches each year. Target the oldest branches, and prune them down to ground level.

Propagation

Although it’s tempting to try planting seeds produced by the plentiful berries, winterberry is more effectively propagated by cutting and rooting stem cuttings, which will grow much faster than seeds. Propagating winterberry holly is best done in late spring through midsummer. Here’s how:

  • Use a pair of clean sheers or pruners to trim several 2 to 3-inch stem tips from a mature female shrub that has produced berries for at least a season.
  • Remove all but the top pair of leaves on each stem.
  • Dip the cut end of the stem into rooting hormone, then insert it into a pot filled with pre-moistened standard potting soil.
  • Cover the entire pot with a plastic cover to keep humidity in and place the container in a shady outdoor location.
  • Periodically water the cuttings, ensuring the soil stays moist but not wet.
  • After a month, remove the plastic cover and continue to grow the cutting in the pot. By fall, the new plant should be ready to transplant into the garden.

Weed Control

Pests and Diseases

Common Pests and Plant Diseases

Winterberry holly is generally pest- and disease-resistant. However, voles like to chew on the stems of winterberry holly in the winter. In addition, the shrub can be susceptible to leaf spots and powdery mildew, which are rarely serious. Give your shrubs more air circulation to combat leaf spots. An organic fungicide, such as neem oil, is the best treatment for powdery mildew.

Common Problems

Not Producing Berries

If your winterberry does not produce flowers or berries, it could be a gender issue: the right female and male pairs are not located close enough to each other. If you’re still not seeing berries or flowers on your shrubs—assuming all other care requirements are met (including the proper amount of sunlight and water)—the problem could be the shrub’s age. Winterberry hollies only fruit when they’re well established, which can mean as many as two to three years in the ground before you’ll see a display of berries.

Yellowing Leaves

If the leaves on your winterberry holly are turning yellow, the soil’s pH may be higher than 6.5. This shrub does not thrive in neutral to alkaline soil.

Blotchy, Misshapen Leaves

Powdery mildew will show up on winterberry holly as white spots or blotches on leaves. The leaves can also be stunted, curled, puckered, and covered in reddish-purple blotches.

III. Uses and Benefits 

  • Medicinal uses

The berries were used by Native Americans for medicinal purposes, the origin of the name “fever bush”.

The seeds, leaves, bark and berries of the plant can cause nausea and low blood pressure if ingested.

  • Ornamental uses

Ilex verticillata – the American winterberry – is prized as an ornamental plant in gardens for the midwinter splash of bright color from densely packed berries, whose visibility is heightened by the loss of foliage; therefore it is popular even where other, evergreen, hollies are also grown. The bare branches covered in berries are also popular for cutting and use in floral arrangements. In autumn/fall the leaves turn yellow sometimes with tinges of red and orange.

IV. Harvesting and Storage

In suitable growth conditions, common winterberry 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.

Winterberry (Ilex verticillata) Details

Common name Black Alder, Common Winterberry, Winterberry, Winterberry Holly
Botanical name Ilex verticillata
Plant type Native Plant
Hardiness zone 3a, 3b, 4a, 4b, 5a, 5b, 6a, 6b, 7a, 7b, 8a, 8b, 9a, 9b
Growth rate Slow
Harvest time Fall
Height 3 ft. 0 in. - 15 ft. 0 in.
Width 3 ft. 0 in. - 15 ft. 0 in.
Sunlight Deep shade (Less than 2 hours to no direct sunlight)
Soil condition Clay
Flower color Gold/Yellow
Leaf color Black