Sky pencil holly is one of the fastest growing hollies in the genus Ilex. It produces a columnar shrub with clean lines that adds vertical interest to the home landscape. Sky pencil is a Japanese holly that was introduced by the United States National Arboretum in 1992. Sky pencil is easy to grow and needs no pruning to retain the pillared shape. Hollies are susceptible to several leaf diseases, and spider mite feeding can cause leaves to yellow and drop.
Sky pencil is an evergreen holly that grows in a tall, narrow habit. It can get up to 10 feet tall but will only become 2 to 3 feet wide and will remain that width without intervention. The small glossy green leaves are 1/2 to 1 1/4 inch long. Foliage has a serrated edge that is smaller than in larger hollies. Tiny little white flowers pepper the plant in late spring and become dark purple drupes.
Botryosphaeria canker is found on the Japanese hollies and occurs when the plant is exposed to unusually high or low temperatures. Yellow leaves and leaf drop are primary symptoms followed by twig dieback and cankers on bark. The disease is caused by adverse conditions, so prevention entails good cultural practices. Sky pencil should be planted in fall with the root ball just above soil level. Initial irrigation and mulching will help the plant establish without stress and achieve good health to avoid bot canker and the many other fungal or bacterial leaf diseases that cause ornamental plant leaves to yellow.
Sky holly can get several of the usual ornamental pests. Scale is a sucking insect, and its feeding activities can cause leaves to yellow and sometimes fall off. Spider mites are common and can be spotted by the webbing they leave all over the plant. The insects themselves are too small to see with the naked eye. Symptoms of mites can include yellowing of the leaves. Nematodes also can kill hollies. They are common in the South and are microscopic worms that eat feeder roots in sandy soils. These pests can cause leaf yellowing, slow growing and inadequate fertiliser and water uptake.
Thielaviopsis black root rot is common on the Japanese hollies. It starts out with yellowing leaves followed by stunted growth, leaf drop and twig death. If you dig the plant up, you will see black bands across the normally white roots. Eventually the entire root system will blacken and die. The disease is found in soil and can remain in infected nursery pots unless they are sterilised. You can apply a preventive fungicide soil drench, but there is no cure once the holly has acquired the disease. Phytophthora root rot has very similar symptoms and occurs where soils are too wet.
Sky pencil grows in either full sun or partial shade and is tolerant of a wide range of soils, provided the area is well drained. You can even grow the holly in a container. This Japanese holly thrives in moist, acidic soil. The foliage will yellow with chlorosis when planted in alkaline soils due to an inefficiency in iron uptake. Sky pencil needs no supplemental irrigation if planted in partial shade with plenty of organic matter in the soil. Plants grown in sun should receive occasional water during summer and hot months.