Photo: USDA-NRCS PLANTS Database / Herman, D.E. et al. 1996. North Dakota tree handbook. USDA NRCS ND State, Public domain · source

Conifer · Pine family (Pinaceae)

Colorado blue spruce

Picea pungens · also: Blue spruce, Colorado spruce

The Colorado blue spruce comes from the Rocky Mountains and is a popular garden and Christmas tree here, above all for its silvery-blue needles. That colour comes from a waxy coating on the very stiff, sharply pointed needles. It grows 15–25 m tall, usually 10–15 m in gardens, with a regular cone shape about 5 m wide. It loves full sun and isn’t fussy about soil, but it is shallow-rooted and acidifies the soil beneath it. For small gardens there are slow-growing and dwarf forms. In our mild, damp climate, though, it is susceptible to green spruce aphid, which turns the inner needles brown.

Caution: The needles are sharply prickly: don’t plant it next to a path, a play area or a seating area.

Updated on 10 October 2026

Light
Full sun
warm and bright
Moisture
Normal
no wet feet
Legal basis
Any garden soil
any pH
Hardiness
Throughout Belgium
no protection needed
Size
15–25 m (in gardens usually 10–15 m)
tall

Key facts
Pruning months	May–June
Height	15–25 m (in gardens usually 10–15 m)
Native to Belgium	No, planted
Good for bees, butterflies and birds	Yes, for birds
Poisonous to people and pets	Not known to be poisonous

Identify

Colorado blue spruce: how do you recognise it?

Habit: Tree of 15–25 m, usually 10–15 m in gardens, forming a regular cone about 5 m wide with branches down to the ground.
Needles: 2–3 cm, square in cross-section, very stiff and sharply pointed, blue-grey to silvery blue (‘Glauca’), all round the shoot on small woody pegs.
Bark: Grey and scaly.
Cones: Hanging, light brown cones of 6–10 cm with crinkly scale edges.
Difference from Norway spruce: Norway spruce has green, less prickly needles, longer cones (10–15 cm) and hanging side shoots.

Pruning: May–June

Identify by feature: Prickly needles

Looks like it, but isn’t

Norway spruce Picea abies: green, less prickly needles, longer cones (10–15 cm) and hanging side shoots. Difference from Norway spruce

In your garden

Why grow it?

A striking silvery-blue colour, all year round.
A neat, regular cone shape that needs little pruning.
Fully hardy and resistant to cold winds.
Dense branches give birds shelter in winter.
There are forms for every garden, from dwarf globes to a large specimen tree.

Colorado blue spruce: where does it grow best?

Full sun: in shade it grows thin and less blue.
Any free-draining soil; it doesn’t like waterlogging.
Its roots are shallow and dense, and the fallen needles acidify the soil: little grows under the crown.
In a garden, allow for 10–15 m in height and 5 m in width: don’t plant it right in front of a window or against the house. For a small garden, choose a slow-growing or dwarf form.

Light: Full sun
Legal basis: Any garden soil
Moisture: Normal
Size: 15 m tall, 5 m wide
Hardiness: Throughout Belgium, no protection needed

Goes well with

Winter heath: Flowers pink or white in winter at the sunny base, and tolerates the slightly acid soil around conifers.
Ornamental juniper: A low evergreen conifer with green or yellow foliage for contrast.
White dogwood: Red stems in winter: a superb contrast with the silvery blue.
Japanese maple: Red leaves and fiery autumn colour next to the cool blue.

Good and bad companions

Goes well with

Like the acid soil under this tree: heather, rhododendron, japanese skimmia, raspberry, highbush blueberry, witch hazel, broom, gorse
Tolerate the shade under this tree: oregon grape, rhododendron, oleaster, japanese skimmia, garden privet, camellia, laurustinus, box-leaved honeysuckle

Maintenance

Colorado blue spruce: when and how to plant it?

Plant in September–October or March–April, root-balled or in a pot.
Don’t plant deeper than it was growing before, and water after planting and during dry spells in the first two summers.
For a small garden, choose a slow form such as the compact cone ‘Fat Albert’ or the dwarf ‘Glauca Globosa’.
A root-balled Christmas tree can go outside after the holidays: keep it indoors only briefly and somewhere cool, and let it acclimatise for a few days in a cold garage before planting.

Care

Watering: In dry spells for the first two years; after that only in long, dry summers.
Feeding: Not needed.
Lower branches: Keep the lower branches: without them it loses its shape, and they won’t grow back.
Green spruce aphid: Check in February–March for small green aphids on the needles: tap a branch over a sheet of white paper.

Tip: A blue spruce as a Christmas tree? Choose one that was grown in a pot: it has more roots than a tree dug up with a root ball and establishes better after the holidays.

Colorado blue spruce: when to prune it?

Pruning months: May–June.

When: Dead, diseased and broken branches can be removed at any time of year. To keep it compact, shorten the new shoots in May–June.

How:

Never cut back into bare branches: a spruce won’t regrow there.
A spruce that has lost its top will grow a new one if you tie a side branch upright.

Caution: Susceptible to green spruce aphid: in spring, brown needles drop from the inside of the tree.

Pruning: when and how · Pruning calendar and basic rules

Propagation

Sowing: Sow in spring in a tray. The seedlings vary in colour from green to blue; nurseries select the bluest.
Grafting: Blue varieties such as ‘Hoopsii’ and ‘Koster’ are grafted; that is a job for the nursery.

Colorado blue spruce: how does it get through the winter?

Hardy throughout Belgium: no protection needed.

Fully hardy: it comes from the cold Rocky Mountains.
After a mild winter green spruce aphid can build up fast: look for aphids in February–March.

Diseases and pests

Green spruce aphid: Brown needles dropping from the inside of the crown in spring, especially after a mild winter. In February–March, tap a branch over white paper; if you see lots of small green aphids, spray with a product based on plant oil or soap.
Spider mite: In hot, dry summers the needles turn dull and yellowish, with fine webbing. Hose the tree down during dry weather.
Lower branches dying: Often caused by a canker fungus, sometimes with white drops of resin on the branches. Cut dead branches back to the trunk in dry weather.
Less blue: Older needles turn greener, and in shade it is less blue. Give it full sun.

Through the year

February: Check for green spruce aphid: tap a branch over white paper.
March: Planting season; keep watching for green spruce aphid.
April: Last month for spring planting.
May: Pinch back new shoots to keep it compact.
June: Last month for shortening the new shoots.
July: Watch for spider mite in hot, dry weather; water young trees.
September: Planting season starts.
December: Keep a root-balled Christmas tree indoors only briefly, somewhere cool.

Use

What can you use it for?

Garden and landscape: Specimen garden tree with a striking blue colour; also as a Christmas tree with a root ball.
For wildlife: Dense branches give birds shelter in winter.

Good for wildlife

Birds: Berries, seeds or insects as food, or a place to nest.

You and this species

Did you know?

Native to the Rocky Mountains. The blue colour comes from a waxy coating on the needles.
The scientific name ‘pungens’ means ‘pricking’: anyone who grabs it will understand why.
It is the state tree of Colorado; the well-known blue form ‘Koster’ was selected in Boskoop at the end of the 19th century.
In the wild, Colorado blue spruce is by no means always blue: the colour ranges from green to silvery blue. Nurseries select the bluest trees and propagate them by grafting.
The well-known silvery-blue cultivar ‘Koster’ was selected by the Koster nursery in Boskoop in the Netherlands.

All species · Identification key · Pruning calendar