Culture
Easily grown in average, medium moisture well-drained soils in full sun to part shade. Tolerant of a wide variety of soils ranging from moist to dry and from sand to clay. Prefers light, moist, acidic soils with good drainage. Established plants have some tolerance for drought. Plants may struggle with the heat and humidity of summers in the deep South in USDA Zones 8-9. Plants are dioecious (male and female flowers on separate plants), so both male and female plants must be present in order for the female plant to be pollinated and produce fruit.
'Sky Pencil' is an all-female cultivar which needs a male pollinator in order to produce fruit. Maintains columnar shape without pruning. May not be reliably winter hardy throughout USDA Zone 5 where it should be grown in a protected location with a winter mulch.
Noteworthy Characteristics
Ilex crenata, commonly known as Japanese holly or box-leaved holly, is a dense, multi-branched, evergreen shrub with a rounded form that typically matures to 5-10’ tall and as wide. It is native to forests, thickets and mountain slopes in Japan, Korea, China and eastern Russia (Sakhalin). It is noted for its ovate to elliptic, crenate to serrulate, glossy, spineless, evergreen, deep green leaves (to 1 1/4" long) which are attractive all year, 4 petaled white flowers which bloom in 3-7 flowered cymes in late spring (May-June), and black rounded somewhat inconspicuous fruits (drupes to 1/4” diameter) which mature in fall on pollinated female plants.
Genus name comes from the Latin name Quercus ilex for holm oak in reference to the foliage similarities (holm oak and many of the shrubs in the genus Ilex have evergreen leaves).
Specific epithet is in obvious reference to the crenate margins of the leaves.
'Sky Pencil' is an exceedingly narrow, fastigiate form which grows somewhat slowly in a vertical, pencil-like column to 10' tall but only 2-3' wide. A typical 4-6' tall specimen may only be 10-12" wide. 'Sky Pencil' is an introduction of the U.S. National Arboretum in Washington, D.C.
Problems
No serious insect or disease problems. Spider mites can be troublesome. Nematodes are a problem in the South.
Uses
Mass or group. Hedge. Borders. Incorporate into a foundation planting.