Tree & Shrub articles - by Brian Baldwin

Trees Tell A Story by Brian Baldwin

If you could travel back in time to walk through Saskatoon's river valley as it was 100 year ago, you would find the valley lined by Manitoba maple, birch, poplar and green ash trees. Because much of the river valley is now preserved and protected, native trees can still be seen lining the banks of the river in stands nearly unaffected by the growth of the city around them. In a sense, therefore, you can walk through portions of Saskatoon's river valley and see it almost as it was 100 years ago.

Settlers brought with them new trees from distant lands. Of these trees, American elm has been the most popular and successful. These stately, arching trees line the streets of almost all of Saskatoon's older neighbourhoods. But, the westward movement of Dutch Elm Disease, continues to pose an ever-increasing threat of destruction to Saskatoon's elms, and because elms constitute approximately 80% of Saskatoon's mature tree canopy, the city's character would be vastly altered by their loss.

While most Saskatoon residents of the past seemed content with planting mainly elm, a few pioneering residents experimented with unusual trees. Some have survived to maturity, and can now be seen as examples of shade trees suitable for replacement of elms. The following is a list of some of the better examples of Saskatoon's uncommon trees.

Bur oak is a long-lived stately tree, fully adapted to our environment. Eighty years ago, few residents experimented with this tree, so although it is gradually becoming more popular, there are very few mature oaks in Saskatoon. Two of the city's best examples of mature bur oak can be seen in a yard in the 900 block of Temperance Street. One of the two oaks in this yard towers well above the neighbour's two-story house, and rivals the neighbourhood elms for size and grandeur. A third excellent example of mature bur oak is found in the 300 block of Saskatchewan Crescent West. Surrounded and almost hidden by elms, this tree stands beside a large silver maple, another tree under-utilized in Saskatoon's past.

Silver maple is a tree that can surprise you. I have walked past magnificent examples of silver maple for years without noticing them, until one autumn day a classic "Canada Flag" maple leaf on the sidewalk alerted me to the tree's presence. Three excellent examples of enormous silver maple can be seen in the 300 block of Saskatchewan Crescent West. One stands beside the oak mentioned above, the other two stand almost directly across the street. Test yourself with the last one. Test yourself on the last one: Can you spot the large silver maple visible from the intersection of Temperance Street and Lansdowne? It took me years to notice it, yet it's right there!

Little-leaf-linden is another shade tree that has recently begun to gain in popularity. Of the few mature lindens that exist, one of the best examples stands just south of the university campus in the 1100 block of Elliot Street. A new house and stone fence were recently constructed very close to the tree, and although the fence disrupted the tree's roots rather badly, this tree seems to have survived the construction. Another example of a mature linden can be seen directly adjacent to Lorne Avenue at the intersection of 4th street. This multi-trunked linden would perhaps be larger than the one on Elliot street if it had not lost its top as a sapling and regrown from the ground as numerous shoots.

A mature Ohio buckeye is a true rarity in Saskatoon. Such trees are perhaps most easily noticed in autumn when their deep red coloration causes them to stand out against our limited pallet of gold and yellow fall colour. One of the very few Ohio buckeye trees to have reached mature stature in Saskatoon stands in a back yard along Queen Street. The tree can be seen from 9th avenue, rising above a concrete block fence. A second mature Ohio buckeye stands in front of a house on the south side of University Drive, in the 900 block.

Saskatoon's coniferous landscape has long been dominated by white and Colorado blue spruce. Although neither of these trees is native to the city, their popularity among early residents is evident in the many mature examples found within the city.

Scots pine is perhaps Saskatoon's most popular pine. The tree is remarkably tolerant of hot dry summers and long cold winters. Many excellent representatives of this species can be observed in the city, but an exceptional example of Scots pine stands on a front lawn just west of Broadway on 10th street. It's a tree you cannot miss!

Less common pines found in Saskatoon include lodgepole, ponderosa and Swiss stone pine. Some of our best examples of rare pines were planted by Dieter Martin in ambitious designs on the University of Saskatchewan campus.

Lodgepole pine is the forest tree of Cypress Hills. It is found in limited numbers in Saskatoon. Perhaps the best example of this species is the lone tree standing in the experimental plots just west of the intersection of 14th street and Preston Avenue. Several sister trees to this one can be seen further along that fence line to the west. They may be less obvious but they are no less spectacular representatives of their species.

Possibly the city's largest ponderosa pine is found on the university campus, in a grouping of Scot's pine, directly west of the Veterinary Medicine building. With needles almost a foot long, this tree has a tall straight trunk, and the rounded top that is characteristic of mature pines in their natural range.

Swiss stone pine is another rarity. This attractive, slow growing, full-to-the-base pine maintains a perfect "christmas tree shape" if grown in full sunlight. To truly appreciate the softness of the needles, you simply have to touch them. Of the few excellent example of this tree I know in Saskatoon, two stand as a matched pair along the south wall of the PFRA building, across from Education's parking lot on the campus. The best Swiss stone pine in the city is possibly the one standing against the south wall of a house on 33rd Street, approximately a block east of Avenue P. It's gorgeous!

While there are certainly many more unusual species of trees that have been tried and proven successful in Saskatoon, those mentioned here should offer some good examples of trees we can grow in Saskatoon. If readers are aware of other unusual mature trees in Saskatchewan, they may wish to write to Brian Baldwin at the Department of Horticulture Science, University of Saskatchewan, 51 Campus Drive, Saskatoon, Saskatchewan, S7N 5A8. A further reference of interest is Saskatchewan Trees of Renown, published by the Saskatchewan Forestry Association in 1985.

Other rare trees since publication:

Celtis occidentalis in Nutana back alley (can't remember street number)
Butternuts on Saskatchewan and Poplar Crescent.
White pine in Sutherland and a back alley in Simpson Crescent
Norway Spruce near 5 corners and on 14th street.
Salt Tree on 12th
Mayday tree on campus at Little Stone Schoolhouse.
Mugo pine on campus at Murry Building.

© 1996 Brian Baldwin


Evergreens Browned Off by Winter by Brian Baldwin

Having just emerged from one of the most miserable winters in recent memory, that last thing you probably want to hear about is something relating to winter. Unfortunately, browning of evergreens was such a major problem this winter that many people are wondering what to do.
Usually only the tender evergreens such as cedars show winter browning. This winter, however, some of our toughest junipers, pines and spruces were browned off. On Colorado spruces, the damage usually shows up as more of a purple than a brown patch.

Trees that are newly planted (within the previous two growing seasons) are more susceptible than their fully established counterparts. Many of your newly planted pines may show total browning of the newest growth.

On established trees, much of the browning occurred in association with street lights. A tree only knows that winter is approaching by monitoring the lengthening nights of late summer. Pine or spruce branches that are growing directly in the zone lit by a streetlight have their nights artificially lengthened, so these branches cannot tell that winter is approaching, and do not adequately prepare. Sodium vapour (orange) street lights causes greater problems than mercury vapour (blueish) lights. This is because the red wavelengths of the light are most influential in telling the plant the length of the day, or night.

If you pines or spruces have brown needles, there's a good chance that the bud at the end of the branch is still alright. The best thing to do is wait for new growth to emerge and mask the symptoms of damage. If no new growth has occurred by mid-June, the buds are probably dead. In that case, severely browned branches can be removed, and all living parts of the tree left. Small pines or spruces will not be disfigured for life, and will generally recover an acceptable form after a few seasons.

Cedars are the real problem. In general, cedars growing along north or east facing walls will be alright, but those along south or west facing walls will be damaged. This is because exposure to late-afternoon sun, when daily temperatures are at their highest, results in a daily freeze/thaw cycle in their tissues which is very damaging. If the south or west side of your cedars have turned brown, wait until mid-June and then crumble the dead bits out using your fingers. Anything that is crisp enough to break off when gently squeezed is dead and will not come back to life. If you wish to replace cedars growing along a west or south exposure, you should consider an upright form of Rocky Mountain juniper. These have the same columnar form, but are tougher than cedars. If you really want cedars, and your house faces west, plant them along the back wall, where they will receive an east exposure.

© 1996 Brian Baldwin


Forsythia by Brian Baldwin

Of the flowering shrubs available to prairie gardeners, forsythia (Forsythia ovata) holds a special place in our hearts because it provides the very first springtime flowers. If you should see a shrub covered in bright yellow bell-like flowers in the next few weeks, it is almost certainly forsythia.

While early flowers grant forsythia great appeal, these flowers are not risk-free. Although their branches are fully hardy to prairie winters, forsythia flower buds are hardy only to -38°C. For this reason, forsythia may fail to flower after an extremely cold winter, or may only flower on the lowest branches - those that were covered with snow.

Regular readers of this column will know that the main factor that kills a plant in winter is the formation of ice inside its cells. The hardiest of trees are those which dehydrate their cells to the point where ice formation inside of them is simply impossible. Semi-hardy plants like forsythia have adopted a somewhat less reliable, but no less remarkable strategy of winter survival called supercooling.

Supercooling involves cooling pure water below 0°C without the formation of ice. To understand it we need to consider a basic principle of ice formation.

Liquid water consists of many closely packed water molecules arranged in a haphazard manner. If you visualize individual water molecules as bricks, a glass of water would be somewhat like a barrel into which bricks had been randomly tossed - they're close enough to be touching, but in no particular order. When water's randomly organized molecules become aligned and locked together in an precise and regular pattern, you have ice. An ice crystal could therefore be visualized as a brick walls, and from the plant's point of view, it's large enough to do some damage.

Normally, when pure water is chilled to 0°C, the first two molecules (bricks in the wall) will lock together using some microscopic impurity in the water as a template. A single bacterium, a speck of dust, or some other very tiny object is necessary to provide the initial template upon which the crystal begins. This template is known as the "ice nucleator." Once the first two molecules have locked together, the necessary pattern has been established, and the crystal growth continues as other molecules lock on.

For plants, the trick to supercooling is maintaining the water in the cells in such an ultra-pure state that no nucleators are present. With no impurities present to act as templates, the first two water molecules will not connect and the first microscopic ice speck will not form. If nucleation can be avoided, water can remain liquid at remarkably low temperatures. In fact, absolutely pure water will remain liquid until its temperature has dropped to -38.1°C.
If the internal temperature of a forsythia's buds never quite drop to forty below, the plants will flower in spring. This has also been suggested as a reason far more plant species are hardy in areas that never quite reach -40°C.

`Northern Gold' is the only prairie-hardy forsythia cultivar. Saskatoon residents who would like to see this plant blooming should keep an eye on the corner of the City Hall grounds directly across from the Frances Morrison Library where a cluster of these shrubs should be flowering soon - if the winter of '96 wasn't too much for them.

© 1996 Brian Baldwin


Grafting Offers Endless Possibilities by Brian Baldwin

Grafting is the process of joining two or more different plants and permitting them to grow as one. Although the techniques of grafting sometimes seem like mysterious surgical procedures accessible only to highly-specialized professionals, a bit of instruction is usually all that is needed for most people to accomplish successful grafts.

Of course certain limitations exist. Only closely related plants will form a compatible union. Generally this means apple-to- apple, rose-to-rose, but some plants permit you more leeway. Saskatoons can be grafted to the roots of cotoneaster, mountain ash or hawthorn because all these plants are members of the rose family. Lilacs and green ash can be grafted together because they are both members of the olive family, but plants in the cactus family are perhaps the most amenable to grafting.

The bright pink or orange-topped cactus plants that are sometimes sold as "flowering" cacti in supermarkets, are actually small grafted plants. The pink portion is not a flower, but a stem from a cactus that mutated, losing its normal green colour, and adopting a more flamboyant hue. These colourful mutants are grafted onto their plain green rootstocks which not only supply them with water and soil nutrients, but also feeds them through photosynthesis. The non-green mutants cannot perform photosynthesis, so they are living on their host much like a parasite.
Nurseries often carry `Walker' weeping caragana grafted to a trunk of `Sutherland' upright caragana. This union creates a small tree with a vertical trunk that abruptly turns and weeps back to the ground. In the last decade these little weeping trees have become quite fashionable, but like many garden ornaments they are met with conflicting opinions. Some people love them, while others view them as little more than a living form of the tacky pink flamingoes that dotted urban lawns in the 1960's.

Grafting solves many horticultural problems. Some of the most floriferous lilacs also have the disagreeable habit of suckering from their roots. The attractive-blooming lilacs can therefore be grafted to the roots of less attractive, non-suckering types to capture the best qualities of both.
In many apple-growing areas, orchard trees are grown on dwarfing rootstocks. A dwarfing rootstock greatly reduces the size of the tree. For example, on their own roots, `Granny Smith' apple trees become very large, requiring high ladders to harvest. If `Granny Smith' buds are grafted to dwarfing rootstocks, the same size and quality of fruit can be produced, but the entire tree may never exceed a few meters in height.

If a friend or neighbour has a particular type of apple you have always admired, why not try grafting a few twigs from that tree onto your own. If you'd like to try it, now is the time to act. Simply collect some healthy twigs about the thickness of a pencil. Wrap them in damp paper towel in a plastic bag, and store them in your refrigerator. When the new leaves are just breaking this spring, these dormant twigs can be grafted to your existing tree.
Once you know how it's done, there is very little to limit you. I've seen a single tree that produced over 100 different types of apple. Guides are available, or you can take a class.

© 1996 Brian Baldwin


Delayed Winter Injury Appearing by Brian Baldwin

The winter of 1995-1996 in Saskatchewan was one of the hardest on trees in the past thirty years. While the damage on evergreens had become very conspicuous by late winter, many deciduous trees only began to show signs of winter damage with the arrival of hot weather.
A wide array of trees are showing winter dieback, but apples are among the hardest hit. This is understandable if you consider the breeding programs that generated most of our prairie-hardy fruit trees.

None of the excellent large-fruited apples grown in commercial orchards have adequate hardiness to survive the average prairie winter. On the other hand, the Siberian crabapple is as hardy as a rock. Unfortunately, fruit quality on a Siberian crab is also distinctly rock-like. Because of this, breeding programs have focused on finding a reasonable compromise between the hardiness of Siberian crabapples and excellent quality of large-fruited cultivars. This means most of our apples are intermediate, with fair to good fruit quality and fair to good winter hardiness. With only intermediate hardiness, however, fruit trees often show some dieback following a very severe winter.

What you are probably seeing:
Soon after the first hot days arrived this spring, you may have noticed the leaves on your apple (or other tree) becoming stunted and wilted. The new leaves on some branches failed to expand to full size and many of them may have dried and died right on the tree.

The problem is a result of damage to the plant's water conducting tissue that occurred last winter. It can be visualized as something similar to bursting of frozen water pipes in a building. With only a portion of the plant's water conducting pipelines still functional, enough moisture would have been reaching the top of the plant during the cool spring when the leaves were small. Once the leaves began to enlarge, and the weather became hot, the damaged vascular system could no longer replace water at the rate it was being lost so the top portion of the tree began to die.

The best thing to do is keep your tree well watered for the rest of the growing season to minimize the drought effects it is already feeling. The larger and older the limbs, the better they will have handled the winter, so although some of the younger branches will probably die completely, new ones will emerge along the trunk to replacing them. By the end of summer, those branches which are dead and brittle, can be pruned cleanly away to make room for the re-growth that will likely follow.

© 1996 Brian Baldwin


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