Reverting Back

by Phil Caldwell

White spruce, Picea glauca, although probably not as common as Norway or Colorado Spruce, is often seen in landscapes. Probably the most common form of White Spruce is Picea glauca ‘Conica,’ better known as Dwarf Alberta Spruce. Dwarf Alberta, in my opinion, is often overplanted, probably because of the need for a fairly compact, pyramidal evergreen that stays small and grows slowly. Alberta is one of the few that fits that requirement. Actually, it may be overplanted because the choices are limited.

The history and habit of Dwarf Alberta Spruce is kind of interesting. In the early 1900s seedlings were found by plant people from the Arnold Arboretum, under a White Spruce in Alberta, Canada, that appeared much smaller and to have a tighter growth habit. After transplanting several of these seedlings and growing them on for several years, many remained dwarf and the cuttings propagated from them also formed dwarf plants. Hence the introduction of Picea glauca ‘Conica,’ better known as Dwarf Alberta Spruce. The seedlings were from a “Witches broom” on the White Spruce, a genetic mutation or abnormality sometimes found on conifers. Some witches brooms are caused by insect or disease problems and must be destroyed, but the more interesting and beneficial brooms are usually the source of cuttings used to introduce new varieties of dwarf conifers. Many dwarf pine and spruce varieties are the result of witches brooms.

In the case of Dwarf Alberta, and some other plants introduced from witches brooms, the cultivar can revert back. Have you ever seen a Dwarf Alberta with a full sized spruce growing out the side of it? Not far from my house there is a very boring entryway planting that includes two Dwarf Albertas, one on each side of the company sign. The plants are fairly sizeable by Dwarf Alberta standards, probably about 8-10 feet tall and quite full. One of the plants looks perfectly normal, the second plant has a Spruce tree, about 5 feet tall growing out the upper side of it where it has reverted back to it›s natural habit. Needles and growth rate are no longer like Dwarf Alberta, but rather their habit is typical of White spruce. I have no idea what percentage of the Albertas revert back to common White Spruce, but the number is quite small and this doesn’t present a problem. If you ever notice this abnormal growth, it can simply be pruned when it is only a few inches in size. Lack of attention, or maybe even lack of knowledge, is the only reason the crazy full grown trees continue to grow.

Doesn’t Mother Nature constantly create fascinating interest in the plant world!

— Phil Caldwell is a past president of NHLA (1989) who now lives and works in Maine.