Sky Pencil Holly

You Can't Miss This Columnar Shrub

Sky Pencil holly (image) is proportionately thin. Its plant form is considered columnar.
Pencil-thin 'Sky Pencil' holly exhibits an interesting plant form. 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 craves flashy names. Plant taxonomy lists the genus and species as Ilex crenata.

Sky Pencil holly is categorized botanically as a broadleaf evergreen shrub. 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 been duped into thinking these shrubs (especially 'Hetzii') to be boxwoods, which exhibit a similar foliage.

In fact, a common name sometimes used for Ilex crenata is "box-leaved holly."

Shrub Characteristics and the Male Pollinator Question

Sky Pencil holly is a relatively slow-growing, columnar shrub that reaches 4-10 feet in height, with a width just a small fraction of that. When my own shrub reached 6 feet tall, its width was only 14 inches at the widest point. The "column" is narrowest at the base, slowly tapering out along the plant's ascent skyward.

These shrubs are dioecious; read this article to learn how to tell male and female holly apart. Sky Pencil is strictly a female cultivar (she does not come with a corresponding "mate"). Yet a male plant is needed to pollinate the female if you want berries. So how does one solve this dilemma?

Fortunately, the matter is not as hopeless as it sounds, at first. I suspect that any type of male holly plant will allow you to achieve pollination. My own Sky Pencil apparently gets pollinated annually by a 'Blue Prince' holly that is way over on the other side of my 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 like the berries.

Planting Zones, Sun and Soil Requirements

The parent species, Ilex crenata is indigenous to the Orient. Sky Pencil holly is often listed for planting zones 6-8. I have grown mine successfully in a microclimate (namely, the south side of the house) in zone 5.

My own plant has performed well in full sun. But this narrow, columnar shrub is listed as a bush that tolerates shade. 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 "privacy fence" using 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, if your landscaping tastes run toward the minimalistic.

    Personally, I find these shrubs most useful in foundation plantings. Columnar shrubs are often placed strategically at the corners of such planting beds. But a pair of Sky Pencil hollies would also be a logical choice flanking a house entry (be it a full porch or just a simple landing area) at the center of a foundation bed, where the intent is to create symmetry.

    Care: How to Prune

    Fortunately, this columnar shrub retains its trademark shape without pruning. If you do choose to prune it (for whatever reason), the bush responds well to pruning. For example, mine is planted in a spot where I do not wish it to grow too high. So I periodically trim off excess growth at the top; the plant eventually generates new growth where the trimming took place, prompting me to prune again (and so on). I choose to let my 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.

    When I feel like being more meticulous with my pruning, I pinch the tips off as many branches as I can. This care causes the shrub to become bushier. In terms of timing, read this article to learn when to prune holly.

    If, like me, you wish to grow the shrub in zone 5, my advice would be to 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 (I use bungee cords) around the shrub at strategic points so as to pull the branches into the center; this will avert potential damage due to the accumulated weight of heavy snow or ice.

    Outstanding Features

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

    When landscaping for small spaces, a horizontally compact shrub that injects vertical interest into your design can be a real boon -- if you can find one. Sky Pencil holly is one of these rare shrubs. Its columnar plant form is also sometimes called "fastigiate." The Latin word, fastigium refers to a slope converging with another to form an apex; in the plant world, verticality will be the most noteworthy feature of a specimen said to be "fastigiate."

    This shrub is generally deemed to be a slow grower. Indeed, in my own experience, it grew slowly the first few years. But for me, the growth rate picked up once the shrub was established. Still, if you need a tall (but not too tall), skinny shrub for a tight spot -- and do not wish to commit yourself to frequent pruning -- this could be the plant for you.

    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 reputedly 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 cozy niche you are trying to fill in a small space. It can be grown in zones 5-8.

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