Tree · Pinaceae
Colorado Blue Spruce
Picea pungens
Settle it into full sun, cool air, and well-drained ground, and your blue spruce will keep its silver glow for decades.
Full sun
Every 7–14 days
USDA 2–7
30–60 ft · 9.1–18.3 m
Overview
If you have ever stopped to admire a Colorado blue spruce, you already know why it wins hearts, with its soft silver-blue needles and that tidy pyramid shape. It grew up in the cool, dry heart of the central Rocky Mountains, where the air stays crisp and water drains away fast. Once you picture that mountain home, caring for one in your own yard starts to feel a lot less mysterious.
Think of this as a patient, slow-growing evergreen that is in no hurry at all, which is good news if you worry about keeping up. Given years and space it can rise past 60 feet and spread 20 feet across the bottom, so it shines as a standout specimen or a windbreak rather than something tucked into a corner. The needles do end in genuinely sharp tips, prickly enough that most browsing animals leave it well alone.
It feels right at home through the cold north, hardy from zone 2 to zone 7, and it brushes off winters that would defeat plenty of other trees. The part to watch is heat paired with humidity. Set it in a muggy southern garden and it tends to thin out and lose its lower branches, so the cooler and breezier the spot you can offer, the more it will reward you.
Care
The short version: give it full sun, cool air, and rich, well-drained soil that never stays wet. Water it deeply while it is young, leave it plenty of room to grow, and after that you can mostly relax and let it be.
Light
Offer your blue spruce full sun, ideally 6 or more hours each day, and it will thank you with the fullest growth and the brightest blue color. A little afternoon shade is fine, and it even helps in warmer regions, but a tree left in deep shade grows sparse and fades.
Water
While a tree is young, water it deeply and keep the soil evenly moist without ever letting it turn soggy, since standing water is one of the rare things that can take this tree down. As it grows up and settles in, your spruce becomes pleasantly drought tolerant and looks after itself, though a deep drink during a long dry spell is always welcome.
Soil
Plant it in rich, moist, well-drained loam, and take heart that it adapts to most soils as long as water keeps moving through. A pH anywhere from 5.5 to 7.0 suits it just fine. The single thing it cannot forgive is ground that stays wet, which rots the roots.
Temperature
This is a tough mountain tree, content from a bitter -51°F (-46°C) all the way up to about 86°F (30°C). It is heat, not cold, that tests its limits. Long stretches of warmth and humidity wear it down and leave the door open to disease.
Humidity
Blue spruce loves it dry and airy, the very opposite of a steamy greenhouse. Damp, still air is exactly what lets needle-cast fungi get a foothold, so the more open and breezy its spot, the healthier your tree will stay.
Feeding
A settled spruce in reasonable soil rarely needs feeding at all, which is one less thing to fuss over. If a soil test ever shows a real shortfall, a balanced slow-release tree fertilizer in spring is all it asks for. You can safely skip the routine yearly feeding, since this tree neither needs nor wants it.
Pruning
Keep your pruning light and never cut the central leader, since that upright shoot is what gives the tree its lovely shape. Take out only dead, diseased, or damaged branches, and do it in late winter or a dry spell so fresh cuts do not invite Cytospora canker.
Repotting
A blue spruce really wants to live in the ground rather than a pot, so repotting rarely comes up beyond settling a young nursery tree into its forever spot. If you are holding one in a container for now, let roots circling the pot or slipping out the drainage holes be your gentle signal that it is time to plant it out.
Size & spacing
Plan ahead for a big tree, because a grown 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 from the start and keep it well clear of buildings, walkways, and power lines, and you will save yourself trouble later.
When to plant
Because blue spruce stays green all year, there is no harvest to time, only the kindest window for planting. Aim for spring once the soil has thawed, or early fall while the roots still get a few warm weeks to settle in before the cold arrives. The one stretch to avoid is the heat of midsummer, when a brand-new tree has a hard time keeping its young roots supplied.
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 worries with a blue spruce turn up first in the needles or on one fading branch, and a lot of it comes back to heat, humidity, or soil that holds too much water. The good news is that spotting trouble early often lets you slow it down well before it spreads. Find what matches your tree below, then step in while your help still makes a difference.
Lower limbs dying back under a crust of bluish-white resin
Cytospora canker tends to move in on trees already tired out by drought or heat, taking one scattered lower branch at a time. The telltale sign is a hard, bluish-white crust of dried sap near the base of a struggling branch. No spray will cure it, so the kind thing to do is prune the dead wood out during dry weather, wipe your tools clean 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
Lower needles turning brown and falling as the tree thins upward
If the oldest inner needles brown and fall and the tree starts thinning from its lowest branches upward, the likely culprit is needle cast, often the Rhizosphaera fungus, creeping up from the bottom. Borrow a hand lens and look for neat rows of tiny black dots along the needles, something a healthy tree never shows. You can help by opening the tree up for airflow, keeping the foliage dry, and treating new growth with a fungicide for at least two seasons in a row.
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 leader drooping over like a shepherd's crook, then dying back
When the leader bends over like a candy cane and dies back, the trouble is usually the white pine weevil, whose larvae tunnel down inside that top shoot. In spring, look for pinhead holes weeping sap on last year's leader. Cut the dead leader out below the damage before the adults can escape, then gently tie up one 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
Speckled, bronze-tinged needles under a veil of fine silk
Needles that go dull and speckled under a faint haze of silk usually point to the spruce spider mite, which flares up in hot, dry, dusty weather. Tap a branch over a sheet of white paper and watch for little specks that crawl. Knock them back with a hard jet of water, and turn to horticultural oil in the cool of spring or fall while the mites are still 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
Here is reassuring news if you share your home with pets or little ones: the blue spruce is not poisonous. The only real thing to keep an eye on is the needles, which come to sharp points that can scratch skin or poke a small child near the eyes. A curious pet that nibbles a mouthful might feel briefly queasy, and that truly is as bad as it gets.
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 feel sick for a little while, but nothing more serious than that.
Dogs None
Dogs are safe around it. Those sharp needles prick more than they poison, so at worst a big mouthful leaves a dog briefly queasy.
Horses None
Horses have nothing to worry about. The bristly, sharp needles hold no poison and are too unpleasant to make good grazing.
Rabbits None
Harmless to rabbits, and the bristly foliage is not something most of them will bother to nibble.
Livestock None
Cattle, goats, and sheep can browse nearby without being poisoned. The sharp needles tend to keep them off it anyway.
Birds None
Birds are in no danger from it at all. Many of them happily shelter and nest among its dense, prickly branches.
People None
Not toxic to people. The only thing to mind 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 you will find for the garden are named cultivars, each picked for a certain color, shape, or size, so you can choose one that fits your space. A handful show up far more often than the rest, ranging from full-size giants all the way down to gentle rock-garden dwarfs.
Hoopsii
Hoopsii is a dense, pyramidal favorite prized for the most intense silvery-blue needles of the group, growing to around 30 to 50 feet.
Fat Albert
Fat Albert keeps to a friendly 8 to 15 feet in a broad, full pyramid, which makes its bright blue needles a lovely choice for smaller yards.
Baby Blue
Baby Blue is a semi-dwarf with a neat, even cone to about 15 to 20 feet, dressed in closely set silvery blue-gray foliage.
Montgomery
Montgomery is a slow dwarf that fills out into a broad cone or globe only 2 to 3 feet across over the years, which earns it a happy home in rock gardens and foundation beds.
How to propagate
Blue spruce comes along either from seed or by grafting, and which you pick really depends on how much that signature blue matters to you. One path is slow but forgiving, the other more exacting but dependable.
SeedModerate
Sow stratified seed in spring · Several years to reach landscape size
You can grow the species from seed, and while it is a slow road that takes several years to reach any real landscape size, it is wonderfully simple. Sow in spring after a cold, moist stratification to coax germination along. Just remember the seedlings vary in color, so the famous blue is never a sure thing.
GraftingDemanding
Late winter onto seedling rootstock · Several years
The named blue cultivars such as Hoopsii and Fat Albert will not come true from seed, so they are grafted instead. The work happens in late winter onto a seedling rootstock, and the young graft still wants several years to settle in. This is careful, exacting work, so it suits an experienced propagator far better than a first-timer.
Myths
Many people take the Colorado blue spruce for a carefree, long-lasting tree that will grow happily in any corner of North America.
In truth it comes from the cool, dry central Rocky Mountains, and it has a hard time once it is planted outside that climate. Through the humid East and Midwest it often thins out and sheds its lower branches as needle casts and Cytospora canker take hold, and several extension programs no longer recommend it for those areas.