Sky Pencil Holly

You Can't Miss This Columnar Shrub

Sky Pencil holly (image) is proportionately thin. Its plant form is considered columnar.
David Beaulieu

Taxonomy and Botany of Sky Pencil Holly

'Sky Pencil' holly has one of those cultivar names that succeeds in being descriptive while also "selling" successfully in a market that favors flashy names. Plant taxonomy lists the genus and species as Ilex crenata.

Sky Pencil holly is grouped botanically with the broadleaf evergreen shrubs. A related shrub is Ilex crenata 'Hetzii'. Both are types of Japanese holly, which is valued for its small, tightly-packed leaves.

Many a casual observer has made the mistake of thinking these shrubs (especially 'Hetzii') to be boxwoods, which have similar leaves. In fact, a common name sometimes used for Ilex crenata is "box-leaved holly." Like boxwood bushes, this plant has leaves with fairly smooth edges (not prickly edges, as many types of hollies have).

Shrub Characteristics and the Male Pollinator Question

Sky Pencil holly is a slow-growing, columnar shrub that reaches 4-10 feet in height, 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.

Holly shrubs are dioecious; that is, there are separate male and female plants. Sky Pencil is strictly a female cultivar (she 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.

So how does one solve this dilemma?

But the matter is not as hopeless as it sounds, at first. The presence of any of a number of different types of male holly plants will allow you to achieve pollination. This gardener's own Sky Pencil apparently gets pollinated annually by a 'Blue Prince' holly that is way over on the other side of his landscape.

If you wish to stick with Japanese hollies, you can use Ilex crenata 'Beehive' (a male cultivar) as a pollinator. 'Beehive' is similar to 'Hetzii' in its growth habit, only it stays shorter (2-3 feet tall), being something of a dwarf.

The small, greenish-white flowers of Sky Pencil are unimpressive, but when pollination does occur, black berries will be produced (the same color as on Ilex crenata 'Hetzii' and the aptly named "inkberry"). While not showy, the black berries do offer something of a novelty, just because of their unusual color. In addition, the wild birds eat the berries.

Planting Zones, Sun and Soil Requirements

The parent species, Ilex crenata is native to eastern Asia. Sky Pencil holly is often listed for planting zones 6-8, but some gardeners report success growing the plant in zone 5 in a microclimate (a sheltered, relatively warm location, such as on the south side of a house).

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, you would generally want to 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).

It will grow best in a 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 acidic.

Uses in Landscaping

There are two different ways to build a "living privacy fence," that is, a barrier that uses plant material:

  1. Traditional hedges composed of one type of plant, sheared to form a uniform wall.
  2. Looser borders, featuring a number of different plants in layers.

Sky Pencil hollies could work well as a component in either. 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.

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). One could use them in the same fashion at the entrance to a driveway. It is possible to grow them in containers, as well. All of these observations suggest a comparison with dwarf Alberta spruce trees, which are used in similar ways. But dwarf Alberta spruce lacks the unusual, columnar shape sported by Sky Pencil holly shrubs.

Care: How to Prune

Fortunately, this columnar shrub retains its unique shape without pruning. If you do choose to prune it, the bush responds well to pruning. For example, is yours growing in a spot where you do not wish it to grow too high? If so, you can periodically trim off excess growth at the top. The plant will eventually generate new growth where the trimming took place, which will prompt you to prune it again (and so on). Likewise, you may choose to let your bush get as wide as it wants to, but one could also control the size of a Sky Pencil holly through pruning in this dimension if one wished to.

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.

If you wish to grow the 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.

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.

Outstanding Features

As an evergreen, Sky Pencil holly obviously offers winter interest. But this fact only begins to tell the story of its usefulness in landscape design.

When landscaping for small spaces, a narrow shrub that injects vertical interest into your design can be a real blessing. There are not many shrubs that fit this description. Sky Pencil holly is one of these rare shrubs. Its columnar plant form is also sometimes called "fastigiate." 

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. This could be just the right plant for you if you need a bush that:

  1. Is tall (but not too tall).
  2. Is skinny (so that it will fit into a tight spot).
  3. Does not need to be pruned often.

Alternative Columnar Shrubs

Irish juniper (Juniperus communis 'Stricta') is a needled evergreen shrub that grows to similar dimensions and keeps a columnar form. It is a better choice for gardeners who live where it gets very cold, as it can survive a winter in zone 3.

There is a barberry shrub that has a columnar form, also. It is called Berberis thunbergii 'Helmond Pillar' and averages 4-5 feet tall by just 1-2 feet wide. Like Sky Pencil holly, this choice is a berry-producer (and it bears red berries, which are showier than black). But unlike Ilex crenata, it is deciduous. Grow it in zones 4-8.

Another "living column" to consider comes from the yew bushes. But Taxus baccata 'Fastigiata' may be too big at 15-30 feet high by 4-8 feet wide to comfortably occupy that tight spot that you are trying to fill in a small space. It can be grown in zones 5-8.