Dwarf conifers | Uconnladybug's Blog

Dwarf Alberta spruce exhibiting reversion to the standard white spruce genotype.

Take a look at this dwarf Alberta spruce! It looks like another kind of spruce is growing right out of it. This is actually a fairly common occurrence in the dwarf Alberta and is called genetic reversion. In the affected part of the tree, the genes have reverted to the original type, Alberta white spruce (Picea glauca). It is not known what causes this but there are some theories. One theory is that genes can somehow be “stored” even though they are not expressed and then later become activated by a factor such as a chemical or the environment. One estimate states that as many as 10-20% of mature dwarf Alberta spruce (Picea glauca ‘Conica’) develop this phenomenon. If this appears in your Alberta spruce, the affected part of the tree should be pruned out at its point of origin or it will eventually dominate the tree as shown below:

Reverted section of tree is becoming as large as the dwarf tree section next to it.

Leaf variegation is also a genetic mutation of the original parent plant and reversion to the original green leaves is sometimes seen in variegated varieties of plants such as Hosta or Norway maple (shown below).

Reversion of variegated Norway maple to green leaves on a section of the tree.

Dwarf conifers in general are actually produced through mutation of their original parent species. They commonly originate from ‘witch’s brooms’, a dense, compact clump of growth, usually with smaller leaves or needles, that occur on a tree. This plant material is propagated by grafting or sometimes by seed from cones in the witch’s brooms. For large scale production of nursery stock, seed is not used because of the genetic variability that would be introduced.

There are many beautiful dwarf conifers with different growth forms, colors and sizes. Growth forms can include the traditional conical shape, mounds, weeping and spreading types. Cultivars are available in a wide array of colors (for plants anyway!) including shades of green (of course), golden yellow, silver, and blue. There is a wide variety of sizes. The size of a dwarf conifer at maturity is really the size of a dwarf conifer at about 10 years of age. The difference between a dwarf and standard conifer is the growth rate, not the maximum potential size. So dwarf conifers are just VERY slow growing, and this characteristic varies from one cultivar to another. This is important to consider for landscape plantings.

I’d like to tell you about a former UConn Horticulturist, Dr. Sidney Waxman.

He devoted his 40 year career to the development of dwarf conifers from witch’s brooms and in those 40 years came up with 40 new cultivars, some of which are commercially available today. Most of his cultivars are from eastern white pine (Pinus strobus) and there are also a few from other conifers. He searched for witch’s brooms around New England. In the early part of his career, he would use a rifle to shoot down cones from the desired part of large trees and his wife was in charge of crawling around below the tree to retrieve the cones. Later, he used tree climbers. Many of Dr. Waxman’s cultivars are named after members of his family or after UConn as seen in some examples here. You can also see some of these beautiful trees right on the UConn campus in Storrs or at the Waxman Conifer Collection site near campus described below:

Waxman Conifer Collection
The late Dr. Sidney Waxman worked for more than 40 years on the selection of new dwarf forms of conifers developed from witches’-broom seeds or tissue. Many of these forms have been named and introduced as University of Connecticut cultivars and are now commercially available in nurseries. Part of UConn’s Horticulture Research Display Gardens, the Waxman Conifer Collection (corner East Rd. and Rte 195) is one of the few sites where the mature forms of Dr. Waxman’s famous dwarf conifers can be seen and studied. Adjacent to town land, its park-like setting makes it a popular destination for town residents seeking a leisurely stroll.

Some of Dr. Waxman’s cultivars: