Southern Alberta is known for endless prairie landscapes with natural cottonwood and some willows. Closer to the mountains and foothills there are plenty of white spruce, pines, aspen, balsam poplar and in some places Douglas fir. Most of the trees you see around yards, fields, streets, parks, and RV campgrounds were planted in the last 120 years. Some natural regenerated bluffs of aspen, spruce and pine occur in areas that are sheltered or protected in the coulees or north slope exposures.
Prior tree selection, planting, care, and maintenance, the site assessment is a must. A site assessment is a thorough and detailed evaluation of site conditions to understand limitations or opportunities for tree and shrub survival, growth, and vigour. Each site is different and understanding and assessing site is vital. When assessing it is important to look at basic soil, water, nutrients as well as space, light, temperature, and wind information which will allow tree/shrub to grow. The assessment can be divided into soil, climate, and space conditions for choosing tree/shrub species
Southern Alberta\’s climate presents unique challenges for gardeners and landscapers, particularly due to its arid conditions and limited water availability. However, with careful planning and the selection of drought-tolerant plants, it\’s possible to create beautiful and sustainable landscapes that thrive even in times of water scarcity. The following are key factors to consider:
Soil
Southern Alberta features a wide variety of soil types, ranging from very rich to very poor. Each soil type can either support or challenge tree growth. The four major soil types and their impact on trees are as follows:
- Clay soil is particularly challenging for tree growth due to its dense particles, which restrict root penetration and limit access to oxygen and moisture. However, certain trees can adapt to heavy clay soils, including native cottonwoods, willows, balsam poplars, aspen, hybrid poplars, elms, and specific ash and linden species.
- Sandy soil is highly porous, low in nutrients, and retains little water. Despite these drawbacks, some tree species, such as pines and junipers, thrive in sandy conditions
- Saline soils pose significant challenges for most tree and shrub species. However, a few shrubs, like silver buffalo-berry, can tolerate moderate salinity levels.
- Compacted soil is a major issue in grazing, urban and developed areas, often caused by road construction or building activity. Compacted soil is even more detrimental to trees than heavy clay, as it lacks the air and water pockets necessary for root growth. The severity of compaction is crucial and ff compaction is limited to the surface, techniques such as tilling and soil amendments can help alleviate the issue. In cases of deep compaction, where 4–6 inches of topsoil overlay the compacted area, shrubs and certain tree species that can grow in shallow topsoil may be viable options.
Wind
Relentless wind is characteristic in the prairies. The prairies are notorious for relentless winds that desiccate the landscape and takes all moisture from the air. Selecting wind-resistant tree species is imperative but not easy task as certain trees exhibit better resilience to wind forces than others, contributing to landscape stability and longevity. Wind direction, speed and frequency can greatly impact tree selection. Strong winds (warm Chinook and cold jet streams) imposed several stresses on trees including stunted growth, shorter branches, smaller leaves, leaning and uprooted trees. Sites exposed to constant wind are usually drier and may need supplemental watering to prevent them from drying out as quickly
Elevation
Elevation in southern Alberta ranges from just below 700 meters near the Saskatchewan border to 1100 meters in parts of Calgary and rising up further west. This elevation difference impacts how some trees grow, as higher elevations are colder and could limit the growth of many trees, especially hardwood species.
Slope is one of the factors for determining vegetation. The vegetation on opposing slopes is vastly different. South-facing slopes are warmer and dryer than north-facing slopes. South-facing slopes dominated by sun-loving species such as pines, larch, birch, poplars, aspen and many others. The north-facing slopes are colder, moist, and have less sunlight and heat. White spruce, and balsam fir are tree species growing more on north-facing slopes
Water
Water is scarce in the prairies and many trees may not develop deep roots to access water that is further from surface. Test your water prior to watering your trees. If it contains high levels of sodium, it will kill your trees fast and not provide chances for them to survive. Some trees can handle drought better than others-e.g. pine are more drought tolerant than poplars, elm, and many others.
Establishment
For the prairie region one of the most common mistakes is planting trees in open areas with no protection from wind and heat, no site preparation and with little watering. Once you know your soil you must do tilling or some soil preparation prior to planting trees. The next thing which is extremely important is that you may need to plant some shrub species and let them grow for 2-4 years prior you plant any tree species. These shrub rows will protect young trees from the relentless wind that takes the moisture from the air and will keep moisture/snow on ground and around roots of newly planted trees longer. Using plastic or any other type of mulch is also a must in southern Alberta.
Care and maintenance
Watering and looking out for insects, weeds and diseases is crucial once you plant trees. Without proper weed control chances of their survival is very limited. Water when you must and do not over water as it will weaken your trees in the long run. For your local conditions there are several things to consider as there are big differences between the areas around Hanna and around Airdrie or Pincher Creek:
- Visit already established shelterbelts, windbreaks, parks, or neighbours to see what trees/shrubs grow there, how they are established and what the good, bad or ugly things about them are.
- Local exposure – northern slopes are colder with more moisture; southern slopes get more light but are drier
- Differences in prevailing winds and local infrastructure
- Amount of snow accumulation during winter and rain during growing season is vastly different – choose trees/shrubs that fit your local moisture availability
It is crucial to understand site conditions prior to choosing any species to plant. Growing conditions inside a city are entirely different than just 10 miles away from a city setting. The same principle applies to small towns and farms. Local site conditions are so variable that you have to pay attention in detail to fully understand what grows best on your property.
The following table is based research papers and publications done by various organizations and institutions as well as through my personal communication with city, town and county staff and visits to many farms, city, towns and hamlets. It does not cover every aspect of tree characteristics but is a starting point for you to consider when planting trees or shrubs on your property.