Plant Identification and Selection

Introduction to the Exam Domain

The Plant Identification and Selection module represents a significant portion of the Red Seal exam for the landscape horticulturist trade. This chapter covers the essential skills for recognizing, classifying, and selecting plants suited to Canadian climatic and edaphic (soil) conditions. You must master botanical nomenclature, selection criteria, hardiness zones, and the particular characteristics of the major plant groups (trees, shrubs, conifers, perennials, annuals, grasses, groundcovers).

The exam assesses your ability to apply this knowledge in real-world landscaping situations. Questions often focus on practical scenarios: choosing a tree for a parking lot, selecting a windbreak hedge, or determining the cause of decline related to poor plant selection.

Botanical Classification and Nomenclature

The Binomial System

Every plant has a scientific name in two parts (genus and species), established by Linnaeus's system. This name is universal and avoids the confusion of common names that vary from one region to another. For example, Acer saccharinum refers to silver maple, while Acer saccharum refers to sugar maple — two distinct species with very different tolerances.

The complete classification structure is as follows:

Taxonomic Rank	Example (Red Maple)
Kingdom	Plantae
Division	Magnoliophyta
Class	Magnoliopsida
Order	Sapindales
Family	Sapindaceae
Genus	Acer
Species	rubrum
Variety/Cultivar	Acer rubrum 'Red Sunset'

Cultivar Nomenclature

A cultivar (cultivated variety) is a horticultural selection with distinct and stable characteristics, propagated vegetatively (cuttings, grafting). The cultivar name is written in single quotation marks, with an initial capital letter, and is not italicized: Acer rubrum 'Franksred' (Red Sunset cultivar). Cultivars are chosen for specific traits: fall colour, disease resistance, compact habit, drought tolerance.

Important Families in Landscape Horticulture

Family	Characteristics	Examples
Rosaceae	Flowers with 5 petals, fleshy or dry fruits	Rose, crabapple, spirea
Pinaceae	Needle conifers, woody cones	Pine, spruce, fir
Cupressaceae	Scales or needles, fleshy cones	Juniper, cedar, false cypress
Oleaceae	Opposite leaves, samara or drupe fruits	Ash, lilac, privet
Fabaceae	Pods, nitrogen fixation	Caragana, black locust
Aceraceae (Sapindaceae)	Opposite leaves, samaras	Maple, Amur maple

Exam trap: botanical family names do not translate literally. The Rosaceae family includes very different plants (strawberry, apple, rose) — never rely on common names for classification.

Hardiness Zones and Microclimates

The Canadian Hardiness Zone System

Canada uses a hardiness zone system based on seven climatic variables: average minimum temperature, frost-free period duration, precipitation, and others. Zones range from 0 (coldest) to 8 (mildest), with sub-zones a (colder) and b (milder). This system is more precise than the American USDA system because it accounts for factors beyond just minimum temperature.

Zone	Average Minimum Temperature (°C)	Example Cities
0a	−56.7 to −53.9	Alert (Nunavut)
1b	−48.3 to −45.6	Yellowknife
2b	−42.8 to −40.0	Saskatoon
3b	−37.2 to −34.4	Winnipeg
4a	−34.4 to −31.7	Ottawa
5b	−26.1 to −23.3	Toronto
6b	−20.6 to −17.8	Vancouver (downtown)
7b	−15.0 to −12.2	Victoria

Practical Application

A plant's hardiness zone indicates the coldest zone where it can survive. A plant rated zone 4 can be planted in zones 4, 5, 6, 7, or 8, but not in zone 3. However, this rule has exceptions related to microclimates.

Microclimate: a local area where climatic conditions differ from the surrounding region. Warm microclimates are found near buildings (exposed south wall), on south-facing slopes, near paved surfaces (heat absorption), or in sheltered valleys. Cold microclimates are found at the bottom of depressions (cold air accumulation), on north-facing slopes, or in wind-exposed areas.

Practical rule: a plant rated half a zone more tender than the region's zone can survive in a favourable microclimate. For example, a zone 5b plant can survive in zone 5a if planted against a south wall with good drainage.

Adjusted Zone Calculation

To determine whether a plant is suitable, compare its hardiness zone to the site zone, adjusting for the following factors:

Wind exposure: reduce by 1 zone if the site is exposed to prevailing winter winds.

Drainage: poorly drained soil reduces hardiness by 1 zone (risk of root freezing).

Snow cover: abundant and persistent snow increases hardiness by 1 zone (insulation).

Proximity to a body of water: increases hardiness by 1 zone (moderating effect).

Calculation example: Site in Montreal (zone 5b), well-drained soil, exposed to north wind, without reliable snow cover. Adjusted zone = 5b − 1 (wind) − 1 (no snow) = 4a. Choose a plant hardy to zone 4a or less.

Plant Selection Criteria

Edaphic (Soil) Factors

Soil pH directly influences nutrient availability. Most plants prefer a pH between 6.0 and 7.0 (slightly acidic to neutral). Some plants require acidic soil (rhododendron, azalea, blueberry, Japanese maple) with a pH of 4.5 to 5.5. Others tolerate alkaline soils (lilac, juniper, white spruce).

Soil Type	Characteristics	Suitable Plants
Sandy	Rapid drainage, poor in nutrients	Scots pine, juniper, caragana
Clay	Slow drainage, rich in nutrients	Silver maple, willow, poplar
Loamy	Balanced drainage/retention	Most plants
Peaty	Acidic, anaerobic	Black spruce, larch, cranberry

Texture test: the ribbon (sausage) method involves moistening a handful of soil and rolling it between your palms. Soil that forms a long, smooth ribbon is clayey; soil that crumbles is sandy; soil that forms a short, brittle ribbon is loamy.

Hydric (Water) Factors

Drought tolerance and flood tolerance are critical criteria. Drought-tolerant plants have adaptations: thick or waxy leaves, deep root systems, deciduous foliage during stress periods. Flood-tolerant plants have roots capable of surviving anaerobic conditions (aerenchyma, adventitious roots).

Moisture Level	Examples of Suitable Plants
Dry (xeric)	Juniper, mugo pine, sedum, yucca, Amur maple
Moderate (mesic)	Red maple, linden, dogwood, hosta
Wet (hydric)	Willow, silver maple, Siberian iris, cattail

Light Factors

Light exposure classification is essential:

Full sun: 6 hours or more of direct sunlight per day.

Partial shade: 3 to 6 hours of direct sunlight, often in the morning or late afternoon.

Light shade: diffuse light, under a sparse tree canopy.

Dense shade: less than 3 hours of direct sunlight, under a dense canopy.

Exam trap: plants labelled "shade-tolerant" are not necessarily "shade-loving." A shade-tolerant plant can survive in shade but prefers sun. A shade-loving plant (e.g., fern, hosta) suffers leaf scorch in full sun.

Usage and Maintenance Factors

Selection must account for the intended use:

Shade tree: large deciduous tree, fast growth, broad habit.

Street tree: tolerant of pollution, compacted soils, de-icing salt.

Windbreak hedge: dense conifers, fast growth, wind resistance.

Privacy screen: evergreen or semi-evergreen shrubs, sufficient height.

Groundcover plant: low growth, dense coverage, weed suppression.

Accent plant: ornamental interest (flowers, fruit, bark, fall colour).

Maintenance frequency is a major economic criterion. Fast-growing plants (poplar, willow, silver maple) require frequent pruning and can damage infrastructure (invasive roots, brittle branches). Slow-growing plants (oak, spruce) require less maintenance but take longer to reach mature size.

Major Plant Groups

Deciduous Trees

Deciduous trees lose their leaves in autumn. They provide summer shade and allow light through in winter. Their selection must account for mature size, form, growth rate, and tolerance to urban conditions.

Species	Zone	Mature Height	Characteristics
Red maple (Acer rubrum)	3-8	15-20 m	Red fall colour, tolerates wet soils
White oak (Quercus alba)	3-8	20-25 m	High longevity, strong wood, slow growth
Littleleaf linden (Tilia cordata)	3-7	15-20 m	Pollution tolerant, good structure
Green ash (Fraxinus pennsylvanica)	2-6	15-20 m	Fast growth, susceptible to emerald ash borer
Ginkgo (Ginkgo biloba)	4-8	15-25 m	Resistant to insects and diseases, golden foliage

Caution: the emerald ash borer (Agrilus planipennis) has decimated ash trees in eastern Canada. Avoid planting ash in infested regions. Black ash (Fraxinus nigra) is particularly vulnerable.

Evergreen Trees (Conifers)

Conifers retain their foliage year-round. They provide permanent screening and winter structure. Their selection must account for mature width (often underestimated) and de-icing salt tolerance.

Species	Zone	Mature Height	Characteristics
White spruce (Picea glauca)	2-6	20-25 m	Cold tolerant, good wind resistance
Eastern white pine (Pinus strobus)	3-7	25-30 m	Soft needles, fast growth, susceptible to blister rust
Balsam fir (Abies balsamea)	3-6	15-20 m	Pleasant fragrance, drought sensitive
Eastern white cedar (Thuja occidentalis)	3-7	10-15 m	Popular hedge, susceptible to winter burn
Tamarack (Larix laricina)	1-5	10-20 m	Deciduous conifer (loses needles), tolerates wet soils

Exam trap: tamarack is a conifer but it is deciduous — it loses its needles in autumn. Never classify it as evergreen.

Shrubs

Shrubs are woody plants under 5 metres in height, often multi-stemmed. They are used for hedges, borders, foundations, or screens.

Species	Zone	Mature Height	Use
Van Houtte spirea (Spiraea x vanhouttei)	3-8	1.5-2 m	Border, loose hedge, spring flowering
Red-osier dogwood (Cornus sericea)	2-7	1.5-3 m	Winter interest (red stems), wet soils
Common lilac (Syringa vulgaris)	2-7	3-5 m	Fragrant flowering, limestone tolerant
Shrubby cinquefoil (Dasiphora fruticosa)	2-6	0.5-1 m	Long flowering, drought tolerant
Highbush cranberry (Viburnum trilobum)	2-7	2-4 m	Edible red fruits, fall colour

Herbaceous Perennials

Perennials return each year from their roots. Their selection must account for flowering period (to ensure continuous interest), height, and hardiness.

Species	Zone	Height	Flowering Period
Daylily (Hemerocallis)	3-9	60-90 cm	June to September (depending on cultivar)
Peony (Paeonia)	2-7	60-100 cm	May-June
Black-eyed Susan (Rudbeckia)	3-7	60-120 cm	July to September
Hosta (Hosta)	3-8	20-60 cm	July-August (flowers)
Coneflower (Echinacea)	3-8	60-120 cm	July to September

Annuals and Biennials

Annuals complete their life cycle in one season. They are used for colourful beds and containers. Biennials complete their cycle in two years (vegetative growth the first year, flowering and seeding the second).

Type	Examples	Use
Full-sun annuals	Petunia, marigold, zinnia	Beds, containers
Shade annuals	Impatiens, tuberous begonia	Shaded beds
Drought-tolerant annuals	Portulaca, gazania	Rock gardens, dry soils
Biennials	Pansy, stock, foxglove	Spring and summer beds

Ornamental Grasses

Ornamental grasses provide texture, movement, and winter interest. They are divided into clumping grasses (tufts) and spreading grasses (invasive rhizomes).

Species	Zone	Height	Growth Type
Miscanthus (Miscanthus sinensis)	4-8	1.5-2.5 m	Clumping
Switchgrass (Panicum virgatum)	3-8	1-1.8 m	Clumping
Blue fescue (Festuca glauca)	4-8	20-30 cm	Clumping
Common reed (Phragmites australis)	3-8	2-4 m	Spreading (invasive)

Exam trap: spreading grasses like common reed can become invasive and are prohibited in some regions. Always check the growth type before recommending a grass.

Selection for Special Conditions

Plants for Saline Soils (Roadside Areas)

De-icing salt (sodium chloride) damages plants through ionic toxicity and osmotic dehydration. Salt-tolerant plants have exclusion or tolerance mechanisms.

Species	Zone	Salt Tolerance
White spruce (Picea glauca)	2-6	Good
Scots pine (Pinus sylvestris)	2-7	Good
Caragana (Caragana arborescens)	2-7	Excellent
Sea buckthorn (Hippophae rhamnoides)	3-7	Excellent
Rugosa rose (Rosa rugosa)	2-6	Good

Plants for Compacted Soils

Compacted soils (parking lots, pedestrian areas) limit root growth and aeration. Adapted plants have superficial roots and tolerate hypoxia.

Species	Zone	Characteristics
Amur maple (Acer ginnala)	2-7	Compaction tolerant, small tree
Hackberry (Celtis occidentalis)	2-7	Very tolerant of urban conditions
Japanese pagoda tree (Styphnolobium japonicum)	4-7	Tolerant of pollution and compaction
Littleleaf linden (Tilia cordata)	3-7	Good urban tolerance

Plants for Shaded Areas

Selection for shade must distinguish dry shade (under trees, root competition) from moist shade (north side of buildings).

Condition	Suitable Species
Dry shade	Spurge, barrenwort, male fern, periwinkle
Moist shade	Hosta, astilbe, fern, impatiens
Light shade	Brunnera, coral bells, foxglove, spotted deadnettle

Calculations and Measurements in Plant Selection

Calculating Plant Spacing

Spacing depends on the plant's mature width and the desired effect (dense hedge, natural border, alignment).

Formula for dense hedge: spacing = mature width × 0.6 to 0.75

Example: Emerald cedar hedge (Thuja occidentalis 'Smaragd') with a mature width of 1.2 m. Spacing = 1.2 × 0.7 = 0.84 m. Round to 0.8 m (80 cm).

Formula for tree alignment: spacing = mature width × 1.5 to 2.0

Example: Red maple with a mature width of 12 m. Spacing = 12 × 1.5 = 18 m minimum.

Calculating the Number of Plants

Formula: Number of plants = Total area (m²) ÷ (spacing × spacing)

Example: A 20 m² bed with perennials spaced 0.3 m apart. Number = 20 ÷ (0.3 × 0.3) = 20 ÷ 0.09 = 222 plants.

Exam trap: for triangular (staggered) spacing, density is higher. The formula becomes: Number = Area ÷ (spacing² × 0.866). For 20 m² with 0.3 m spacing: 20 ÷ (0.09 × 0.866) = 20 ÷ 0.078 = 256 plants.

Calculating Soil Volume for a Tree

Formula: Volume (m³) = π × (planting pit radius)² × depth

Example: Planting pit 1.2 m in diameter and 0.9 m deep. Radius = 0.6 m. Volume = 3.1416 × (0.6)² × 0.9 = 3.1416 × 0.36 × 0.9 = 1.018 m³.

Canadian Standards and Best Practices

Planting Standards

The Tree Planting Guide from the Canadian Nursery Landscape Association (CNLA) establishes best practices for planting. Key points:

The planting pit should be 2 to 3 times wider than the root ball, but no deeper than the root ball height.

The root collar (trunk-root junction) must be at finished grade level, never buried.

Staking is only necessary for large-canopy trees or in windy areas; it should be removed after 1 to 2 years.

Mulch should be applied 5 to 10 cm thick, avoiding any contact with the trunk (leave a 5 cm gap around the trunk).

Plant Quality Standards

The CAN/CSA Z262 standard (National Standard of Canada for nursery stock) defines quality requirements for plants sold in Canada. It specifies:

Minimum container sizes (e.g., #1 container = 3 L, #2 = 7 L, #5 = 15 L).

Caliper requirements for trees (trunk circumference measured at 30 cm from the ground).

Tolerances for defects (broken branches, girdling roots, trunk wounds).

Tree Caliper	Trunk Circumference (cm)	Minimum Height (m)
50 mm	5	2.5
60 mm	6	3.0
80 mm	8	3.5
100 mm	10	4.0

Invasive Species Legislation

The Invasive Species Act (Canada) and provincial regulations prohibit the importation, sale, and planting of certain species. Common invasive species to avoid:

Common buckthorn (Rhamnus cathartica)

Tartarian honeysuckle (Lonicera tatarica)

Common reed (Phragmites australis subsp. australis)

Garlic mustard (Alliaria petiolata)

Japanese knotweed (Fallopia japonica)

Exam trap: some species still sold in nurseries (like buckthorn) are prohibited in several provinces. Always check local regulations before recommending a species.

Step-by-Step Selection Process

Step 1: Site Analysis

Measure the available space (height, width, depth).

Assess light exposure (full sun, partial shade, shade).

Test drainage (dig a 30 cm hole, fill with water, measure infiltration time — less than 2 hours = good drainage, more than 12 hours = poor drainage).

Measure soil pH (test kit or pH meter).

Identify constraints (power lines, foundations, underground utilities, sidewalks).

Step 2: Define Objectives

Function (shade, screen, colour, wildlife habitat).

Acceptable maintenance level.

Budget (initial cost + maintenance over 10 years).

Aesthetics (form, texture, colour, seasonal interest).

Step 3: Pre-selection

List plants suited to the adjusted hardiness zone.

Filter according to site conditions (soil, light, moisture).

Eliminate invasive or prohibited species.

Check nursery availability.

Step 4: Final Selection

Compare pre-selected plants using weighted criteria (hardiness, maintenance, aesthetics, cost).

Choose the plant that best meets all criteria.

Document the selection with the complete botanical name (genus, species, cultivar).

Pitfalls to Avoid

152.Confusing common names: "maple" can refer to several very different species. Always use the complete botanical name in your answers.

153.Ignoring mature width: candidates often calculate mature height but forget width. A 20 m tall tree with a 15 m spread does not suit an 8 m wide space.

154.Neglecting invasive roots: willows, poplars, and silver maples have roots that damage foundations and pipes. Never recommend them near buildings.

155.Forgetting the root collar: planting too deep is a major cause of tree mortality. The root collar must always be at grade level.

156.Confusing hardiness and heat tolerance: a plant hardy to zone 2 is not necessarily adapted to the heat of zone 7. Also check the maximum tolerance.

157.Choosing plants not suited to salt: near roads and sidewalks, de-icing salt kills sensitive plants. Use the salt-tolerant plant list.

158.Planting invasive species: buckthorn, Tartarian honeysuckle, and common reed are prohibited. Check the regulations.

159.Underestimating cast shade: a tree planted south of a building will cast shade that affects plants to the north. Calculate the shade cast at solar noon.

160.Ignoring flowering periods: for a perennial border, continuous flowering must be ensured. Choose species with complementary flowering periods.

161.Confusing conifer types: tamarack is deciduous, cedar has scales (not needles), pine has needles in bundles of 2 to 5. These distinctions are frequently tested.

Summary

Binomial nomenclature (genus + species) is universal and mandatory for accurate identification. Cultivars are noted in single quotation marks.

Canadian hardiness zones (0 to 8) account for seven climatic variables. The adjusted zone must be calculated based on microclimate, wind, drainage, and snow cover.

Selection criteria include soil pH, drainage, light exposure, drought and salt tolerance, and intended use.

Major plant groups (deciduous trees, conifers, shrubs, perennials, annuals, grasses) each have specific selection and maintenance characteristics.

Spacing and plant count calculations are essential for planning. Use the formulas: spacing = mature width × 0.6 to 0.75 (hedge) or × 1.5 to 2.0 (alignment).

Canadian standards (CNLA, CSA Z262) define planting best practices and plant quality.

Invasive species legislation prohibits the planting of several species. Always check the regulations.

Key Points for the Exam:

Competency	Detail to Remember
Identification	Complete botanical name, family, distinctive characteristics
Hardiness	Hardiness zone, microclimate adjustment
Selection	Multiple criteria (soil, light, water, use)
Calculations	Spacing, plant count, soil volume
Standards	Root collar at grade, pit 2-3× wider
Regulations	Prohibited invasive species

Exam Tips

Read questions carefully: multiple-choice questions often include distractors with similar common names. Identify the exact botanical name before answering.

Memorize hardiness zones for Canadian cities: Ottawa (5a), Toronto (6a), Winnipeg (3b), Vancouver (7a), Montreal (5b), Halifax (6a). These references will help you contextualize questions.

Learn distinctive family characteristics: opposite vs. alternate leaves, flowers with 4 vs. 5 petals, samara vs. drupe fruits.

Practice spacing calculations: calculation questions are common and require a clear method. Always write the formula before calculating.

Review invasive species: one in two questions covers regulations. Know at least five prohibited species.

Use the elimination process: for selection questions, first eliminate plants that are not hardy, then those not suited to the soil, then those not suited to the light. Usually only one valid option remains.

This chapter covers all the knowledge needed to succeed on Red Seal questions about plant identification and selection. Mastering these concepts, combined with calculation practice and memorization of standards, will allow you to approach this section with confidence.

Plant Identification and Selection