Evergreen Ornamentals: Coniferous Evergreens (Hort 1008)
Unit 2: Trees
Tree Species Overview
Picea abies - Norway spruce
Picea glauca - White spruce
Picea omorika - Serbian spruce
Picea pungens var. glauca - Colorado blue spruce
Tsuga canadensis - Canadian hemlock
General Identification Characteristics of Picea (Spruce spp.)
Evergreen: Retains green needles year-round.
Shape: Broadly conical to thin and spire-like.
Foliage: Needle-like leaves attached to a leaf peg.
Leaf Peg Characteristics: When a needle is pulled away from the twig, the leaf peg remains on the twig.
Related Structures:
Leaf cushion
Leaf peg
Pulvinus (a specific structure in plant biology).
General Information on Picea (Spruce spp.)
Transplanting: Spruce trees are easy to transplant in large sizes due to shallow, spreading root systems.
Mechanization: Dutchmaster nurseries mechanize the process, allowing for quick tying and digging for transport.
Windthrow Susceptibility: Very shallow root systems make spruce trees susceptible to windthrow.
Research Reference: Windthrown Sitka spruce
Detailed Species Information
Picea abies (Norway Spruce)
Origin: Europe
Hardiness Zone: 3
Height: 25 m
Form: Pyramidal
Dense and compact when young, develops pendulous branches with age.
Growth Rate: Medium
Leaf Characteristics
Type: Evergreen, needle-like.
Length: ½ - 1 inch long.
Shape: Four-sided, stiff, slightly curved, tapering to sharp point, angled forwards.
Color: Dark green.
Seed Cone Characteristics
Size: Large, cylindrical, 4-6 inches long.
Cone Scales: Thin, stiff, diamond-shaped, tapering to a slightly toothed tip.
Position: Pendulous at branch tips, abscising intact.
Color: Pale brown.
Twig and Bark Characteristics
Twig: Orange to brown new growth; non-resinous buds with reddish to light brown scales.
Bark: Gray-brown; thick and flaking as it matures.
Soil Preferences
Type: Very adaptable; prefers well-drained soils and is drought-tolerant.
Potential Problems: Non-significant susceptibility to mites, spruce gall adelgid, spruce budworm.
Landscape Use
Applications: Suitable for large open spaces, windbreaks, screening, groups, or as Christmas trees.
Cultivars of Picea abies
'Nidiformis'
Dimensions: 60 cm x 1.5 m
Description: Low growing, flat-topped, spreading, dense compact growth, slow growth rate.
Notable Feature: Initially noticed mutation looked like a bird’s nest.
'Pendula'
Description: Dramatic weeping form that requires staking; grows tall if staked, otherwise scrambles.
Cone Production: Produces cones that grow into a pyramidal tree species when planted from seeds.
Quick Recognition for Picea abies
Needles: 4-sided.
Cones: Long cylindrical, measuring 4-6 inches.
Branches: Pendulous secondary branches with fringe characteristics (leaf pegs and cushions).
Picea glauca (White Spruce)
Origin: Canada and northern United States
Hardiness Zone: 2
Height: 25 m
Form: Pyramidal
Growth Rate: Medium
Leaf Characteristics
Type: Evergreen, needle-like.
Length: ½ - ¾ inch long.
Arrangement: Spiral, four-sided, straight to slightly curved, tapering to sharp point.
Color: Pale grey-green to bluish-green, emits an unpleasant scent when needles are crushed.
Seed Cone Characteristics
Size: Small, 1-2.5 inches long; pendulous.
Cone Scales: Thin, flexible, fan-shaped with rounded margins; abscising intact.
Color: Pale brown.
Twig and Bark Characteristics
Twig: Light pale brown, becoming brown; hairless.
Buds: Non-resinous, light brown.
Bark: Gray-brown; thick, flaking scales as it matures.
Soil Preferences
Type: Very adaptable; grows best in moist soils but can tolerate dry soils post-establishment. Urban tolerant (pollution).
Potential Problems: Susceptible to mites, spruce gall adelgid, spruce budworm.
Landscape Use
Applications: Specimens, screening, windbreaks, or as Christmas trees.
Cultivars of Picea glauca
'Conica'
Dimensions: 2.5 m x 1.2 m
Characteristic: Narrow, conical form with fine, short, dense clusters of needles.
Potential Problems: Spider mites, reversion.
'Pendula'
Dimensions: 8 m x 2 m
Feature: Slender form with pendulous branches displaying blue/green needles.
Quick Recognition for Picea glauca
Needles: 4-sided, pale grey-green or blue-green, moderately prickly.
Seed Cones: Smallest cones (rounded margins on scales) in Ontario.
Structural Features: Strong leaf pegs and cushions.
Picea omorika (Serbian Spruce)
Origin: Europe
Hardiness Zone: 4
Height: 20 m
Form: Pyramidal with a narrow top and short arching branches.
Growth Rate: Slow to medium.
Leaf Characteristics
Type: Evergreen, needle-like.
Length: ½ to 1 inch long; flattened with bluntly pointed tips.
Color: Dark green and glossy above with two prominent white bands below.
Needle Arrangement: Needles angle forward at the top of branches.
Seed Cone Characteristics
Size: Small; up to 2.5 inches long; pendulous in the upper canopy.
Color: Violet-purple when young, maturing to reddish-brown.
Cone Features: Taper to a point with stiff rounded scales and slightly toothed margins.
Twig and Bark Characteristics
Twig: Orange to brown, hairy.
Buds: Dark brown.
Bark: Mature bark is brown and scaly.
Soil Preferences
Type: Tolerates various soils, pH adaptable; prefers moist soils but can tolerate dry soils once established.
Culture Notes: Transplants well in large sizes, urban tolerant, no serious pests.
Landscape Use
Applications: Suitable as specimens, in groups, and for screening (noted for being tall, narrow, tough, and reliable).
Cultivars of Picea omorika
'Nana'
Dimensions: 1.5 m x 1.5 m
Description: Dwarf plant with dark green needles and silver-blue bands on undersides.
Quick Recognition for Picea omorika
Needles: Flattened with strong contrast between upper and lower surfaces.
Seed Cone: Reddish-brown with rounded scales and curved stalk.
Picea pungens var. glauca (Colorado Blue Spruce)
Origin: Western North America
Hardiness Zone: 2
Height: 18 m
Form: Pyramidal with dense branching, may lose lower branches due to drought stress.
Growth Rate: Slow.
Leaf Characteristics
Type: Evergreen, needle-like.
Length: 1-1.5 inches long; four-sided, stiff, and sharply pointed (prickly).
Color: Glaucous; new growth is silvery blue-gray (sun-exposed), inner growth is gray-green (shaded).
Seed Cone Characteristics
Size: Cylindrical, 2-4 inches long; pendulous in upper canopy.
Mature Color: Light brown; cones have thin, flexible, diamond-shaped scales that are wrinkled with wavy margins.
Twig and Bark Characteristics
Twig: Initially glaucous, matures to orange-brown.
Buds: Broadly conical, yellow-brown with loose scales.
Bark: Grayish-brown with irregular flaky scales.
Soil Preferences
Type: Prefers rich moist soil, neutral to acidic; well-drained, drought-tolerant to an extent.
Potential Problems: Spruce spider mites, spruce gall adelgid, spruce budworm.
Landscape Use
Popularity: Highly sought-after by public; rapid growth is insufficient to meet demand in Ontario nurseries.
Cultivars of Picea pungens var. glauca
'Hoopsi'
Dimensions: 18 m x 6 m
Form: Pyramidal, silvery-blue.
'Glauca Globosa'
Dimensions: 1 m x 1.5 m
Description: Round and flat-topped, silvery-blue, top-grafted and grown as a standard.
'Waldbrunn'
Dimensions: 50 cm x 90 cm
Description: Round and flat-topped, silvery-blue.
Landscape Mistakes
Tip: Do not prune into a popsicle shape for aesthetic purposes.
Quick Recognition for Picea pungens var. glauca
Needles: Four-sided in colors that include green, blue, silver; sharp pointed.
Seed Cones: Light brown with thin, flexible scales and wavy margins.
Potential Problems Associated with Spruce Species
Spider Mites
Characteristics: Cool-season mites that feed on needle sap, beginning with interior/protected needles.
Prevention: Prevent drought stress and monitor plants frequently.
Canker
Disease: Cytospora; a stem disease caused by fungus.
Impact: Causes girdling and death of affected trees.
Spruce Adelgids
Description: Spruce gall adelgid causes pineapple-like galls at twigs’ base on new growth; galls turn brown and twigs may die by late summer.
Image Reference:
Spruce Budworm
Characteristics: Native and destructive pest primarily affecting spruce and fir forests, notably white spruce and balsam fir.
Lifecycle: Larvae emerge in spring, and feeding can lead to tree mortality.
Tsuga canadensis (Canadian Hemlock)
Origin: Ontario
Hardiness Zone: 3
Height: 20 m
Form: Loosely pyramidal with wide horizontal slender branches and a drooping terminal leader.
Growth Rate: Slow to medium.
Leaf Characteristics
Type: Evergreen, needle-like, < ¾ inch long.
Upper Surface: Small, flat, glossy green.
Underside: Glaucous with two prominent white stomata bands.
Tips: Rounded tips; needles appear to be in rows from the branchlets due to short petioles.
Fruit Characteristics
Type: Cone; small, ¾ inch long, green maturing to brown.
Persistence: Remains on twigs until spring.
Twig and Bark Characteristics
Twig: Slender, flexible, hairy, and drooping.
Buds: Small ovoid with hairy scales, light brown.
Bark: Young bark is flaky and scaly; mature bark is reddish-brown and deeply furrowed.
Soil Preferences
Type: Moist, well-drained, acidic; may tolerate alkaline conditions and high organic matter.
Culture Notes: Prefers part shade but tolerates full sun; important to irrigate well in the fall.
Culture Notes
Growth Conditions: Tolerates shearing; can be cultivated as a hedge.
Potential Problems
Harmful Species: Hemlock woolly adelgid (HWA).
Definition: Invasive species that threaten local ecosystems; harm the trees and surrounding environments when introduced outside their native habitats.
Landscape Use
Applications: Primarily as specimens, in groups, for hedging/screening, or in topiary.
Cultivars of Tsuga canadensis
'Sargentii'/ 'Pendula'
Dimensions: 2 m x 2.5 m.
Description: Semi-dwarf, weeping, and pendulous.
'Cole's Prostrata'
Dimensions: 30 cm x 1.5 m.
Description: Prostrate/low growing with drooping new growth.
Quick Recognition for Tsuga canadensis
Needles: Small, flattened, with short petiole.
Stomata Bands: Present on the undersides of needles.
Seed Cones: Small, ¾ inch long with round scales.
Twigs: Thin and flexible, labeled by drooping terminal shoot.
Comparing Seed Cones
Species for Comparison: Picea abies, Picea glauca, Picea omorika, Picea pungens, Tsuga canadensis.
Study guide
Identification Quiz Topics: Genus, specific epithet, and common names.