Tree · Pinaceae
Colorado Blue Spruce
Picea pungens
Give it full sun, cool air, and well-drained ground, and the blue spruce holds its silver color for decades.
Full sun
Every 7–14 days
USDA 2–7
30–60 ft · 9.1–18.3 m
Overview
Few trees catch the eye like a Colorado blue spruce, with its silvery-blue needles and clean, pyramid shape. It comes from the cool, dry central Rocky Mountains, where the air stays crisp and the drainage is sharp. That mountain home tells you almost everything about how to keep it happy in your own yard.
This is a slow-growing evergreen that plays the long game. Left to its own devices it can climb past 60 feet and spread 20 feet at the base, so it earns its keep as a specimen tree or a windbreak rather than a tuck-in-the-corner shrub. The stiff needles end in genuinely sharp points, prickly enough to keep most browsers off it.
It thrives across the cold north, hardy from zone 2 to zone 7, and shrugs off winters that would finish most trees. The catch is heat and humidity. Plant it in a muggy southern garden and it tends to thin out and drop its lower branches, so the cooler and airier the site, the better it holds its looks.
Care
The short version: full sun, cool air, and rich, well-drained soil that never sits wet. Water it deeply while it's young, give it plenty of room to spread, and otherwise leave it largely alone.
Light
Give a blue spruce full sun, ideally 6 or more hours a day, and it rewards you with the densest growth and the brightest blue. It will take some afternoon shade, which actually helps in hot regions, but a tree stuck in deep shade grows thin and loses its color.
Water
Water young trees deeply and keep the soil evenly moist but never soggy, since standing water is one of the few things that will kill this tree outright. An older, established spruce turns fairly drought tolerant and mostly fends for itself, though a deep soak during a long dry spell pays off.
Soil
Plant in rich, moist, well-drained loam, though the tree adapts to most soils as long as water moves through. A pH anywhere from 5.5 to 7.0 suits it. The one deal-breaker is ground that stays wet, which rots the roots.
Temperature
This is a cold-hardy mountain tree, comfortable from a brutal -51°F (-46°C) up to around 86°F (30°C). Heat is the real limit, not cold. Sustained warmth and humidity stress the tree and open the door to disease.
Humidity
Blue spruce wants it dry and airy, the opposite of a humid greenhouse. Damp, stagnant air is what lets needle-cast fungi take hold, so the more open and breezy the site, the healthier the tree stays.
Feeding
An established spruce in decent soil rarely needs feeding at all. If a soil test turns up a genuine shortfall, a balanced slow-release tree fertilizer in spring is plenty. Skip the routine yearly feeding, which this tree neither needs nor wants.
Pruning
Keep pruning to a minimum and never cut the central leader, which is what gives the tree its shape. Remove only dead, diseased, or damaged branches, and do the work in late winter or a dry stretch to avoid spreading Cytospora canker through fresh wounds.
Repotting
A blue spruce belongs in the ground, not a pot, so repotting rarely comes up beyond moving a young nursery tree into its permanent home. If you do hold one in a container, watch for roots circling the pot or running out the drainage holes as the cue to plant it out.
Size & spacing
Plan for a big tree: a mature specimen reaches 30 to 60 feet (9 to 18 m) tall and 10 to 20 feet (3 to 6 m) wide at the base. Give it that much open room and keep it well clear of buildings, walks, and power lines from the start.
When to plant
Blue spruce is an evergreen, so there is no harvest to chase, just the right window to get it in the ground. Plant it in spring once the soil has thawed, or in early fall while the roots still have warm weeks to settle before winter. Skip the heat of midsummer, when a new tree struggles to keep up with the demand on its young roots.
Northern hemisphere
Southern hemisphere
Typical months for a temperate climate: start earlier in warm zones, later where spring frosts linger.
- Plant: Spring or early fall
- Harvest: Non-flowering; grown for evergreen foliage and pyramidal form
Hardiness
USDA hardiness zones: 2–7
Temperature: down to -46°C
Troubleshooting
Most blue spruce trouble shows up first in the needles or on a single dying branch, and much of it traces back to heat, humidity, or a site that holds water. Catch the early signs and you can often slow a problem before it spreads. Match what you see below, then act while it still does some good.
Dying lower branches with bluish-white resin crusted on the bark
Cytospora canker strikes trees already worn down by drought or heat, killing one scattered branch at a time low on the trunk. The giveaway is a hard, bluish-white crust of dried sap near the base of a dying branch. There is no spray that cures it, so prune the dead wood out in dry weather, sterilize your tools between cuts, and keep the tree watered and mulched.
Fix:
- Prune out and destroy infected branches during dry weather
- Disinfect pruning tools between cuts
- Repeat pruning over two consecutive seasons if needed
- Reduce stress with mulch and watering during drought
Inner needles browning and dropping while the tree thins from the bottom up
This is needle cast, usually the fungus Rhizosphaera, and it works its way up from the lowest, oldest branches. A hand lens shows rows of tiny black dots along the needles where a healthy tree would show none. Open the tree up for airflow, keep the foliage dry, and treat new growth with a fungicide for at least two seasons running.
Fix:
- Improve air circulation by spacing and selective thinning
- Avoid wetting the needles with overhead sprinklers
- Apply chlorothalonil, copper hydroxide, or mancozeb when new needles are about half their mature length, with a second application 3 to 4 weeks later, for at least two consecutive years
- Remove and destroy fallen infected needles
The top shoot wilting into a shepherd's crook and dying
When the leader droops over like a candy cane and dies back, the cause is the white pine weevil, whose larvae bore down inside the topmost shoot. Look in spring for pinhead holes weeping sap on last year's leader. Cut the dead leader out below the damage before the adults escape, then tie up a single straight side branch to train as the new top.
Fix:
- Prune out and destroy the infested dead leader below the larval damage in summer before adults emerge
- Train a single straight side branch to become the new leader
- Apply a labeled insecticide to the leader in early spring where weevil pressure is high
Stippled, bronzed needles laced with fine webbing
Needles that turn dull and speckled under a haze of fine silk point to the spruce spider mite, which flares up in hot, dry, dusty spells. Tap a branch over a sheet of white paper and watch for specks that crawl. Blast the foliage with a hard jet of water, and reach for horticultural oil in the cool of spring or fall while the mites are active.
Fix:
- Hose down foliage with a strong stream of water to dislodge mites
- Apply horticultural oil or a labeled miticide when mites are active in cool spring and fall
- Avoid broad-spectrum insecticides that kill mite predators
Toxicity
Good news for households with pets and children: the blue spruce is not poisonous. The one thing to watch is the needles themselves, which end in sharp points that can scratch skin or poke a small child near the eyes. A pet that chews a mouthful might get a brief upset stomach, but that is the worst of it.
Safe for
People · Cats · Dogs · Horses · Rabbits · Livestock · Birds
Cats None
Not poisonous to cats. A cat that gnaws a mouthful of needles might drool or be sick for a short while, but nothing worse.
Dogs None
Safe for dogs. The sharp needles are more of a poke than a poison, though a big chew can leave a dog with a passing upset stomach.
Horses None
No toxin here for horses. The stiff, prickly needles are unappealing to graze and carry no real risk.
Rabbits None
Harmless to rabbits, and the bristly foliage is not something most will bother to nibble.
Livestock None
Cattle, goats, and sheep can browse around it without poisoning. The sharp needles tend to keep them off it anyway.
Birds None
Birds are in no danger from it. Many actually shelter and nest in its dense, prickly branches.
People None
Not toxic to people. The only thing to watch is the needle tips, which are sharp enough to scratch skin or poke a small child near the eyes.
The needles are stiff, sharp, and bristly and can mechanically poke or scratch skin and eyes, and the species has been noted to cause injury to toddlers from its sharp leaf tips; this is physical irritation, not a poisoning. Chewing on needles may cause mild mouth or stomach irritation in pets.
Varieties
Most blue spruce sold for gardens are named cultivars, chosen for a particular color, shape, or size. A few turn up far more than the rest, and they range from full-size giants down to rock-garden dwarfs.
Hoopsii
A dense, pyramidal pick grown for the most intense silvery-blue needles of the bunch, topping out around 30 to 50 feet.
Fat Albert
A broad, full pyramid that stays a manageable 8 to 15 feet, which makes its bright blue needles a good fit for smaller yards.
Baby Blue
A semi-dwarf with an even, tidy cone shape to about 15 to 20 feet, clothed in closely set silvery blue-gray foliage.
Montgomery
A slow dwarf that builds a broad cone or globe just 2 to 3 feet across over years, earning its place in rock gardens and foundation beds.
How to propagate
Blue spruce is propagated either from seed or by grafting, and the choice comes down to whether you care about that signature blue. One is slow but simple, the other exacting but reliable.
SeedModerate
Sow stratified seed in spring · Several years to reach landscape size
Growing the species from seed works, but it is a slow road, and a tree takes several years to reach any real landscape size. Sow in spring after a cold, moist stratification to push germination along. Keep in mind the seedlings vary in color, so the famous blue is far from guaranteed.
GraftingDemanding
Late winter onto seedling rootstock · Several years
The named blue cultivars like Hoopsii and Fat Albert cannot be trusted to come true from seed, so they are grafted instead. The work is done in late winter onto a seedling rootstock, and the young graft still needs several years to settle in. This is exacting work, better suited to an experienced propagator than a first-timer.
Myths
Colorado blue spruce is a trouble-free, long-lived tree that thrives anywhere in North America.
It hails from the cool, dry central Rocky Mountains, and it struggles once you plant it outside that climate. Across the humid East and Midwest it tends to thin out and shed its lower branches as needle casts and Cytospora canker move in, and several extension programs no longer recommend it for those regions.