Tree · Pinaceae

Douglas Fir

Pseudotsuga menziesii

Give it room, moist soil, and a good while to grow, and the Douglas fir turns into one of the tallest trees in the forest.

Light

Full sun

Water

Every 7–⁠14 days

Hardiness

USDA 4–⁠6

Mature size

39–⁠79 ft · 12–⁠24 m

Pet-safe
Douglas Fir

Overview

The Douglas fir is one of the real giants out west, a fast-growing conifer that can shoot past 80 feet (24 m) in a yard and go way higher out in the wild. Funny thing about the name, though: it isn't actually a true fir, just its own kind of evergreen. You can pick it out by the soft flat needles and the dangling cones with papery bracts that stick out like little mouse tails. And yes, it's the classic Pacific Northwest Christmas tree and a big deal in the timber world.

There are two main types you'll run into at the nursery, and which one you pick really matters. The coast type grows fast and tall and likes the mild, damp weather west of the mountains, while the Rocky Mountain blue form stays smaller, looks bluer, and laughs off hard cold down to zone 4. So why does it matter so much here? Because the wrong seed source for your climate ends up fighting disease all the time.

Here's the thing: this is a tree for space and time, not a quick screen. It wants deep, moist, well-drained ground and full sun, and it really doesn't like drought, packed-down soil, or wet feet at the roots. Plant it well away from the house and just let it do its thing, and you'll end up with a landmark tree that outlives whoever planted it.

Care

The short version: full sun, deep and steadily moist acidic-to-neutral soil that drains well, and lots of open room, since this tree can hit 40 to 80 feet in the yard.

Light

Give a Douglas fir full sun and you'll get the fullest, densest growth out of it. It'll put up with a little partial shade, especially when it's young, but a tree stuck in too much shade just goes thin and leggy.

Water

This tree is intolerant of drought, so it wants soil that stays deep and steadily moist without ever turning into a swamp. Water young trees regularly until they settle in, every 7 to 14 days depending on the weather, and don't let a long dry spell slide by without a drink.

Soil

Plant it in deep, moist, rich loam that drains well and leans acidic to neutral, anywhere from pH 4.5 to 7.2. It won't put up with poorly drained or compacted ground, where root rot moves in fast.

Temperature

Douglas fir is pretty tough about weather, handling anything from -29°F to 90°F (-34°C to 32°C) depending on which form you go with. The Rocky Mountain type takes the worst cold of all, right down to zone 4.

Humidity

Outdoor humidity is just whatever your climate hands you, so there's nothing to mess with. What matters way more is air circulation, since crowded, still air is exactly what lets needle cast settle in.

Feeding

Feed in spring with a balanced fertilizer or one made for conifers and evergreens. It's not really about pushing growth, it's about keeping the tree unstressed, which makes it a lot less likely to catch needle cast.

Pruning

Pruning barely comes up. Just take out the dead, damaged, or diseased branches and leave the natural shape alone, unless you're shearing a Christmas tree.

Repotting

This is a forest tree, not a pot plant, so repotting hardly matters once it's past the nursery stage. Keep an eye on a potted young one for roots circling the pot, growth that stalls, or soil that dries out very fast, all hints it wants the ground or a bigger container.

Size & spacing

A Douglas fir gets big and does it fast, reaching 40 to 80 feet (12 to 24 m) tall with a spread of 12 to 20 feet (3.7 to 6 m). Plant it well clear of buildings, power lines, and septic lines, and give it the open space a landmark tree needs.

When to plant

Douglas fir is a long game, not a one-season crop, so settle in. Chill the seed through late winter, set young trees out in spring once the hard frosts are done, and don't sit around waiting on flowers, because this conifer makes cones instead, and they ripen from late summer into fall.

Northern hemisphere

Sow Feb–Mar
Plant Apr–May
Cones Aug–Oct

Typical months for a temperate climate: start earlier in warm zones, later where spring frosts linger.

  • Sow: Late winter after cold-moist stratification of seed for about 1-2 months.
  • Plant: Spring, after the last hard frost, while trees are small and easy to transplant.
  • Harvest: Non-flowering conifer; cones mature late summer to fall. No ornamental bloom.

Hardiness

USDA hardiness zones: 4–6

Temperature: down to -34°C

Troubleshooting

Most of the time, Douglas fir trouble turns up either in the needles or down at the roots. The needle stuff usually comes back to the wrong seed source in a wet climate, while the scary problems are the ones hiding underground. Find your symptom below and jump on it early, because a stressed tree falls to disease a lot faster than a healthy one.

Severe

Pale, thinning crown with dieback and a fading tree

When the whole crown thins out and pales and branches start dying back, the real problem is usually hiding down at the roots. Armillaria root rot shows up as thick white fungal fans tucked between the bark and wood at the root crown, plus black shoestring-like strands, while Phytophthora root rot rots the roots dark in soil that stays wet or packed-down. There's no spray that'll save an infected tree, so the move is to fix the drainage, stop planting too deep, and pull any badly hit tree before you replant the spot with something tougher.

Fix:

  • Improve drainage and avoid overwatering or planting too deeply
  • Remove and destroy severely infected trees including small roots
  • Replant the site with more resistant species
Setback

Old needles brown and drop, leaving a thin crown

If the older needles go patchy and fall while only the new tips stick around, that's almost always needle cast, a fungus that picks off the oldest needles first. Want to tell which one? Swiss needle cast leaves rows of tiny black dots under the needles, while Rhabdocline leaves reddish-brown blotches on second-year ones. Thin out crowded trees so the air moves, keep the roots watered, and in a wet climate go with Pacific Coast seed sources, because they hold up way better than Rocky Mountain stock.

Fix:

  • Improve air circulation by thinning crowded trees and increasing spacing
  • Keep trees adequately watered and properly fertilized to reduce stress
  • Apply a labeled fungicide at budbreak and as new needles expand where infection pressure is high
  • Remove and dispose of heavily infected fallen needles
Setback

Needles eaten off the branches, starting up top

Fuzzy caterpillars munching their way down from the top of the tree usually mean the Douglas-fir tussock moth or western spruce budworm, and in a bad year either one can strip a tree bare. The trick is to look for egg masses on the bark before they hatch in spring, so you know what's coming. Spray Btk while the caterpillars are still small, and honestly, in a lot of years the natural predators and a native wilt virus knock the whole thing back on their own within a season or two.

Fix:

  • Monitor for egg masses before spring hatch
  • Apply Bacillus thuringiensis (Btk) or a labeled insecticide while larvae are young
  • Allow natural enemies and the naturally occurring wilt virus to collapse outbreaks over a season or two
Cosmetic

Fuzzy white tufts on the needles that curl and yellow

Those fuzzy white tufts? That's the Cooley spruce gall adelgid, a little sap feeder that twists Douglas-fir needles instead of making the cone-shaped galls it builds over on spruce. A few of them aren't worth fussing over, since the bugs that eat them usually keep things in check. If it gets bad, hit it with a dormant horticultural oil before budbreak, and try not to plant near spruce, which is the insect's other home.

Fix:

  • Tolerate light infestations; natural enemies often suppress populations
  • Spray dormant-season horticultural oil or treat before budbreak
  • Soil-applied imidacloprid can control populations on high-value trees

Toxicity

Good news if you've got pets or kids around: Douglas fir is not toxic. That's a big part of why it's been the go-to Christmas tree across so much of the country. A pet that chews on the fallen needles might get a slightly upset stomach, but there's no actual poison to stress about.

Safe for

People · Cats · Dogs · Horses · Rabbits · Livestock · Birds

Cats Safe

Cats are fine with this one. If a cat nibbles a needle or two it might drool a bit or cough it back up, but there's nothing toxic in the tree to worry about.

Dogs Safe

There's nothing here that'll poison a dog. Chewing the sharp needles can leave a dog with a slightly upset stomach, so it's still smart to keep them off a fallen branch.

Horses Safe

Horses can hang out around a Douglas fir no problem. It isn't one of the pines blamed for mare abortion, and the needles don't carry any listed toxicity.

Rabbits Safe

Rabbits have nothing to fear from this tree. Wild ones actually browse the bark and twigs through the winter.

Livestock Safe

Cattle, sheep, and goats can browse Douglas fir just fine. Unlike ponderosa pine, the needles aren't tied to losing a pregnancy in grazing animals.

Birds Safe

Birds are perfectly safe around it, and plenty of them shelter in the thick branches and eat the seeds inside the cones.

People Safe

It's safe around people too. The young spring tips even get brewed into a citrusy tea, though the stiff older needles are best kept away from little hands.

Eating needles can cause mild mouth/stomach irritation with possible vomiting, drooling, or diarrhea, and large quantities of sharp needles could rarely cause GI blockage.

Varieties

Most Douglas firs you'll find for sale are just the plain species, but there are a few named forms worth knowing about if you've got a certain spot or climate in mind.

var. glauca / 'Glauca' (Rocky Mountain blue Douglas-fir)

This one's the smaller, blue-green Rocky Mountain form, hardy down to zone 4 and a lot tougher in the cold than the coast type, even if it grows slower and picks up needle cast more easily where it's wet.

'Fastigiata'

It's a skinny, columnar pick that heads straight up instead of out, so it'll fit into tighter spots than the regular species ever would.

'Pendula'

This is the weeping one, with branches that spill and tumble, and it's grown as an ornamental specimen just for that shape.

How to propagate

Douglas fir comes from seed for regular trees and from grafting for the named cultivars, and neither one is quick, just so you know. Both take a couple of years before you've got something ready to plant out.

SeedModerate

Sow in spring after 1-2 months of cold-moist stratification. · 1-2 years to a transplantable seedling

Seed is how you'd usually grow the regular species. Give the seed 1 to 2 months of cold, moist stratification over the winter, sow it in spring, and figure on 1 to 2 years before you've got a seedling big enough to move. Young trees move easily while they're still small, so get them in the ground before that taproot heads down deep.

GraftingDemanding

Late winter onto seedling rootstock. · 1-2 years

Grafting's the fussier route, and it's really just for the named cultivars like the weeping and columnar forms, since those won't come true from seed. You do the work in late winter onto a seedling rootstock, and even a graft that takes still needs 1 to 2 years before it's a tree you can count on.

Myths

Myth

Douglas fir is a true fir, like the firs in the genus Abies.

Reality

Nope, it's not a true fir at all. See that hyphen in Douglas-fir? That's the giveaway, because the tree sits in its own genus, Pseudotsuga, which actually means false hemlock. True firs hold their cones upright and let them fall apart on the branch, but Douglas-fir cones hang down and drop in one piece, with papery three-pointed bracts poking out between the scales like little mouse tails.

Sources