November 10, 2004 Articles No Comments

By Michael Allen

Written for the Manitoba Gardener Magazine: Volume 7, Number 5, Winter 2004, pp 28-29

The long Prairie winter has traditionally spurred the drive to develop woody landscaping plants with an appeal that adds visual interest to the winter garden. For deciduous, broadleaved plants that are leafless from late September to the middle of May, that special interest usually lies in the colour and/or texture of the bark. However, over-wintering fruiting characteristics may also add appeal. Coniferous evergreens are by far the main winter landscaping attraction because of their contrasting green, often grey-green colour against the snow.

My life centres on trees and plants; so it is natural for me to have favourite plants even in the winter. I am spoilt because having travelled to many places in the world so many of my favourites are found in other countries. I can still present my winter favourites for the Prairies.

Swiss stone pine (Pinus cembra)

This is my favourite Prairie tree, and above all it is the only coniferous evergreen that is suitable for clay-loam soils on the Prairies. In general, evergreens do not generally grow well on Prairie clay-loams and suffer numerous diseases and pests as they grow older. Swiss stone pine, native to the mountains of central Europe and western Asia, is a rare exception. It is also rare in terms of consumer’s being able to purchase this tree. Sadly for unknown reasons, Prairie growers have neglected this tree. This is a very hardy “soft” pine in that the 5 needle clusters are soft and flexible like eastern white pine. The tree has a broad, upright character with some specimens almost columnar looking. On some trees the winter bark takes on a distinct reddish-grey colour. Apart from its evergreen foliage in the winter, this tree has remarkable cones. The ovoid cone starts out greenish-violet in colour and then matures to a purplish-brown colour. Often the mature cones can be more reddish than purple. The seeds, often referred to as pine nuts, are edible. This is the only pine in Canada of which I am aware that has its new twigs covered with distinctly thick, orange-brown hairs.

Ninebark (Physocarpus opulifolius)

I am very attracted to the soft peeling, sandalwood or cinnamon coloured bark of ninebark. I have heard that the origin of the word “nine” in ninebark comes from “cinnamon”. The common ninebark is native to eastern North America, and it was one of my favourites when I lived in southern Ontario. The white flowers give way to the unusual fruit consisting of attractive clusters of stocky red pods called follicles. The plant is moderately drought tolerant, and definitely needs full sunlight to flourish. Ninebark tolerates the clay loams of southern Manitoba, but it would prefer much better drained soils. The plant is sensitive to soils having high alkalinity which makes iron as a nutrient mostly unavailable to the leaves. This nutrient deficiency condition is called chlorosis which causes leaves to go from green to green-yellow and ultimately to yellow white. Usually prominent green veins appear against the yellowish background on the leaves. For summer time foliage, I like the shiny, purple-black leafed Diablo ninebark. The leaves require full sunlight to get that appearance.

Amur choke cherry (Prunus amurensis)

I have two of these trees in my back yard, and this cherry is one of my three favourite deciduous Prairie trees. They do especially well in full sunlight especially to bring out the unique colour of the bark. The most notable winter feature is the slightly peeling, orange-bronze bark somewhat similar to the bark of birches. Unlike most choke cherries, I have never seen this tree infected with black knot fungus disease. The tree is rarely a producer of massive number of cherries, but those that are produced seem to be quickly eaten by the birds. This is a great looking tree but be sure the one that is bought does not have a sun scald crack down one side of the trunk in the nursery or garden centre. The crack will get larger with age, and amazingly most trees I have seen including my own never seem to suffer from the presence of this crack.

Japanese tree lilac (Syringa reticulata ‘Ivory Silk’)

This tree lilac is my second favourite Prairie deciduous tree. These trees make a prominent impact in the urban winter garden if they are grown without competition in full sunlight. Specimen tree will have a single straight trunk with a smooth, lustrous, blackish-brown colour. Horizontal white lenticels (old breathing pores) pepper the bark of the trunk giving it a cherry tree appearance. The summer flowers or panicles are creamy white coloured and spectacular. Let the flowers go to fruit called capsules which contain the seeds. Keep the capsules on the tree over winter. The winter capsules have a cinnamon colour and contrast well with the darkness of the trunk against a snowy garden landscape. Proper selection of this tree in the nursery or garden centre is important to insure specimen tree quality. Never choose a multiple stemmed tree (unless that is your choice); never choose a tree with sucker stubs showing at the base; and never select a tree with a frost or sun scald crack in the trunk.

Delta Hackberry (Celtis occidentalis ‘Delta’)

I especially like my third favourite deciduous tree because of one main reason: it is a geographic and genetic survivor of its parental stock which grows naturally in south-western Ontario. Hackberry is native also to southern Minnesota and south throughout central and eastern United States. Hackberry trees have a light creamy-grey, bark characterized by short ridges that are often referred to as warts. This feature is unlike any other tree or woody shrub grown on the Prairies. The fruit is a purple berry called a drupe, and it can be sweet despite the name of the tree. Hackberry trees are very hardy on the Prairies but if they are planted too close to busy streets, the de-icing salts will readily cause the tree to produce closely spaced masses of misshapen branches and twigs called ‘witches brooms’. These brooms do result in die-back of the branch structure and can lead to the death of the tree.

Nannyberry (Viburnum lentago)

I have a strong affinity to woody plants in the genus Viburnum. My company name is derived from this plant. I see nannyberry in its native aspen parkland habitat as the king of woody shrubs, and often it is a small tree growing up to 9 m (30 ft) high. Of the native Manitoba viburnums, only nannyberry has a unique winter terminal bud. This bud produces the white flower clusters or umbels in the spring. The base of the lilac-pink coloured bud is globe-like and tapers to a long point. This is the most distinguishing feature for winter identification of this species. The black berries are very attractive to song birds as are the fruit of all viburnums. Often the nannyberry plants are stripped of their fruit well before the end of winter. To the human olfactory sense both the fruit and flowers of nannyberry smell unpleasant. I think otherwise. Nannyberries grow almost anywhere including shade, but they become specimens in full sunlight. Their fall leaf colours can be a vibrant purple-red.

These have been some of my favourite woody plants for planting for their winter features. Like all woody shrubs and trees, location and care spells the difference between having a high quality specimen or a struggling sorry-looking plant. The number one problem in urban and acreage yards is crowding. For some strange reason, most people feel that trees and shrubs love to be placed close together. Not so. Over-crowding results in competitive growth stresses between and among woody plants, and also encourages pests and diseases. In an ideal urban Manitoba garden I would like to see beds of suitable perennials and annuals with prominent specimens of one or two trees and a few unifying shrubs. Taller trees would never be planted near fence line or buildings. Woody plant maintenance is the largest undertaking gardeners make in their yards. Starting that effort off right through appropriate planting will produce a fine looking garden with much lower woody plant maintenance.

Written by treeexperts-mb