Sky Pencil Holly (Ilex crenata) is grouped botanically with the broadleaf evergreen shrubs. It is a narrow, column-like Japanese holly, which is valued for its small, tightly-packed leaves. It is a good landscaping option for corners and tight spaces. Like boxwood bushes, this plant has leaves with fairly smooth edges (not prickly edges, like other hollies). The small, greenish-white flowers are unimpressive, but when pollination does occur, it produces black berries that attract many birds in search of a treat.
- Botanical Name: Ilex crenata
- Common Name: Sky pencil holly
- Plant Type: Evergreen
- Mature Size: Can grow up to 10 feet tall and 2 feet wide
- Sun Exposure: Full sun
- Soil Type: Rich soil, drains well
- Soil pH: Slightly acidic to neutral
- Bloom Time: Late spring
- Flower Color: White
- Hardiness Zones: 5 to 8
- Native Area: East Asia
How to Grow Sky Pencil Holly
Sky pencil holly is a slow-growing, columnar shrub that can grow up to 10 feet tall, with a width just a small fraction of that. When one of these holly shrubs reaches 6 feet tall, its width may be only 14 inches at the widest point. The column is narrowest at the base, slowly tapering out the higher it goes.
Many gardeners in the North find that the plant performs best in full sun. This narrow, columnar shrub is listed as a bush that tolerates shade. While the plant will probably survive if located in shade, its growth may be slower and its branching not quite as dense.
If, however, you live at the southern end (zone 8) of the plant's growing range, you may find that the bush profits from being located in a spot that offers partial shade.
But, in the north, avoid growing it on the east side or north side of a house (where there will be more shade than there will be on the south side or west side).
The plant will grow best in well-drained soil. You can promote good drainage in the ground that you are planting in by spading in compost. The soil should be allowed neither to become too wet nor too dry. This shrub prefers a soil pH that is more acidic.
Water your sky pencil holly regularly to help the root system become well established. As a good rule of thumb, check soil surrounding your tree to make sure it is moist, but not soggy. If the leaves become pale green in color this could be an indication that too much water is present in the soil. Apply 2 to 4 inches of organic mulch over the root zone to help keep the soil moist.
Temperature and Humidity
If you wish to grow this shrub in zone 5, the best advice would be to situate it in an area sheltered from winds and mulch it in an attempt to help it through the winter. In summer, mulch will help retain moisture in the soil, which is also important for this shrub.
Fertilize your sky pencil holly tree once annually with a slow-release fertilizer—best if in the spring.
Propagating Sky Pencil Holly
Holly shrubs are dioecious; that is, there are separate male and female plants. Sky pencil is strictly a female cultivar (it does not come with a corresponding "mate" of the same cultivar name). Yet a male plant is needed to pollinate the female if you want berries.
The presence of any of a number of different types of male holly plants will allow you to achieve pollination. If you wish to stick with Japanese hollies, you can use Ilex crenata Beehive (a male cultivar) as a pollinator.
Toxicity of Sky Pencil Holly
The berries of all varieties of holly are known to be poisonous to people and pets. Although, not toxic enough to cause death, swallowing holly berries can cause vomiting, diarrhea, dehydration, and drowsiness. Children have had symptoms after swallowing as few as two holly berries. The symptoms of ingestion by a pet are limited to gastrointestinal upset (vomiting, diarrhea), abdominal pain, and possible drooling, and lethargy.
Growing in Containers
Sky pencil holly shrubs grow well in containers. Unlike other types of holly shrubs, you do not have to worry about prickly leaves when moving it around.
Fortunately, this columnar shrub retains its unique shape without pruning. If you feel like being fussier with your pruning, you could pinch the tips off as many branches as you can. This care causes the shrub to become bushier. Winter is a good time to prune this holly, although it is not the only possible time to prune it.
Another item on your winter-care checklist should be to wrap cords or twine (you can use bungee cords) around the shrub in a few places so as to pull the branches into the center. This will help you avoid the damage caused by having heavy snow or ice build up on the branches.
Sky pencil hollies could work well as a privacy barrier. Alternatively, where the goal along a border is simply to provide definition rather than privacy, a row of these narrow bushes could form an attractive "colonnade" of sorts. The shrub has an interesting enough shape to stand alone and serve as a specimen plant, too. When landscaping for small spaces, this is a great narrow shrub that injects vertical interest.
Many homeowners also find these shrubs useful in foundation plantings. Columnar shrubs are often placed at the corners of such planting beds. But a pair of sky pencil hollies would also be a logical choice flanking a house entry (placed on either side of the door). You could use them in the same fashion at the entrance to a driveway.
This shrub is generally considered to be a slow grower. In fact, for many gardeners, it grows so slowly during the first few years that you may start to question whether you might be stuck with a shrub too small for your needs. But the growth rate will pick up once the shrub is established.
Varieties of Sky Pencil Holly
A related shrub is Ilex crenata Hetzii. The male pollinator, Beehive, is similar to Hetzii in its growth habit, only it stays shorter (2 to 3 feet tall), as a bit of a dwarf.