Tree · Cupressaceae
Green Giant Arborvitae
Thuja 'Green Giant'
A tower of soft, flat green sprays that shoots skyward in full sun, screening out the world faster than almost any evergreen.
Full sun
Every 7–14 days
USDA 5–8
40–60 ft · 12.2–18.3 m
Overview
Green Giant arborvitae grows a tall, dense screen quickly, built from countless flat sprays of soft, scale-like foliage that overlap into a solid green face. It is a hybrid evergreen in the cypress family, a cross of two Thuja species, and it lays down several feet of new growth a year once settled. Set a row of them and the fine green sprays knit together into a continuous wall that blocks wind, noise, and the view beyond.
The name understates the scale of the tree. This one climbs to 40 to 60 feet tall and fills out 12 to 18 feet wide, holding a narrow, tapering pyramid clothed top to bottom in that same soft, scale-like foliage, which keeps its even green straight through winter. The 'Green Giant' name fits the plant exactly. Give it the room its full frame needs and it grows on with almost no fuss.
Beneath the fine green surface it is a genuinely tough tree. It shrugs off most pests and disease, deer tend to pass it by, and its roots take to a wide range of soils. The one condition it cannot stand is a soggy, poorly drained spot, where root rot works into the roots and pulls the whole plant down.
Care
The short version: give the tree full sun, ground that drains freely, and clearance for a mature frame of 40 to 60 feet, then water steadily for the opening year or two while the young roots grip the soil.
Light
Green Giant grows densest in full sun, which packs the flat green sprays tight from the base to the tip. It takes partial sun or light shade, but as the light drops the foliage thins and loosens, opening gaps in the once-solid face.
Water
Keep the soil moist for the first one to two years while the roots take hold, watering roughly every 7 to 14 days. Once settled it can ride out short dry spells, though steady moisture in well-drained soil keeps the new green sprays coming fastest.
Soil
It is not fussy about its footing and takes clay, sand, and most textures between, as long as the ground drains. A moist, fertile, well-drained loam suits it best, and it grows across a wide pH band from 5.5 to 8.0.
Temperature
This is a cold-hardy tree, at ease from about -20°F to 100°F (-29°C to 38°C), which covers USDA zones 5 through 8. It holds its even green through hard winters, though a biting wind can scorch the outer sprays to brown.
Humidity
Ordinary outdoor air suits it, so there is no humidity target to meet. Good airflow between plants matters more, since crowding traps moisture against the dense foliage and invites trouble.
Feeding
In decent soil it rarely needs feeding. If the green looks weak and the growth slow, work in a balanced slow-release tree fertilizer in spring, but skip it on plants already flushing well.
Pruning
Green Giant needs little to no pruning and holds its neat pyramid on its own. Shear the outer sprays in late spring or early summer only to keep it as a hedge, and tie up or remove extra leaders so snow can't pull them apart.
Repotting
This is a landscape tree, not a container plant, so repotting rarely comes up. In a nursery pot, watch for roots circling or pushing out the drainage holes, the sign to get it in the ground.
Size & spacing
Plan for a mature tree of 40 to 60 feet (12 to 18 m) tall and 12 to 18 feet (3.7 to 5.5 m) wide, and space a screen with that full spread in mind. Set them too close and the broad pyramids crowd into oversized plants pressed against the house and lines.
When to plant
Grown for its evergreen foliage rather than any flower or fruit, this tree keeps no bloom or harvest to time. Set new plants out in spring or fall, when the soil is workable and the weather is mild, and let the cooler season settle the roots before summer heat or winter cold arrives.
Northern hemisphere
Southern hemisphere
Typical months for a temperate climate: start earlier in warm zones, later where spring frosts linger.
- Plant: spring or fall
- Harvest: non-flowering (grown for evergreen foliage)
Hardiness
USDA hardiness zones: 5–8
Temperature: down to -29°C
Troubleshooting
A healthy Green Giant rarely gives trouble, and what does go wrong shows first in the color and density of that fine green foliage or in the wake of a rough winter. Learn to read winter burn apart from a pest, and a wet-site decline apart from drought stress, and you can step in before it spreads across the sprays. Match what you see below, then act while it still helps.
Foliage yellowing and thinning as the tree slides into decline
When the color drains toward a sickly yellow and the sprays wilt and thin across the whole plant on wet, heavy ground, the trouble is usually root rot, with Phytophthora taking hold in soil that stays soggy. Lift the soil at the base and the roots read dark, soft, and slimy instead of firm and pale. No easy save exists once it grips, so open the drainage, hold back the water, and pull badly affected plants before it travels.
Fix:
- Improve drainage and stop overwatering
- Avoid planting in low, waterlogged spots
- Remove severely affected plants to limit spread
Foliage bleached brown across the outer sprays after winter
The even green gives way to dry, straw-brown patches on the wind- and sun-facing side, and that is winter burn. The scale-like foliage keeps releasing water through the cold while the frozen roots send none up, so the tissue parches and fades to a bleached tan rather than breaking into spots. A deep soak in fall before freeze-up, mulch banked over the roots, and a wait until fresh green pushes out in spring reveal exactly which sprays pulled through.
Fix:
- Water deeply in fall before the ground freezes
- Prune out clearly dead tissue once new spring growth shows what survived
- Apply mulch over the root zone to extend water uptake
Bare, stripped branches dangling small spindle-shaped bags
Where the dense sprays thin to bare twigs, look for the small tapered cases of the evergreen bagworm caterpillar, which grazes the foliage down and drags its case behind it. Each one measures 0.25 to 2 inches long, shingled over with clipped bits of the plant's own foliage so it reads almost like a tiny green cone hanging off a twig. Pluck them off through fall and winter before the eggs hatch, and touch young larvae with Bt in late spring if fresh cases appear.
Fix:
- Hand-pick and destroy bags in fall, winter or early spring before eggs hatch
- Spray Bacillus thuringiensis (Bt) on young larvae in late spring/early summer, repeating every 7 to 14 days
Branches splayed wide or snapped apart after heavy snow
The tight, tapering pyramid holds snow and ice on its upswept sprays, and the piled weight pries the multiple leaders outward or cracks them clean through. Sweep the snow off the branches before it settles and freezes, and draw the upright stems together with soft ties so the narrow form stands true. A single-leader plant, with one clean central stem, sidesteps most of this splaying.
Fix:
- Gently brush snow off before it accumulates and freezes
- Tie multiple leaders together with soft material for support
- Prune cleanly broken branches
Foliage dulled to a stippled bronze under fine webbing
The rich green flattens to a dull, dusty bronze speckled with pale flecks, and a faint webbing threads the sprays, the mark of spider mites feeding in hot, dry heat. Hold a sheet of white paper beneath a branch, tap it, and the tiny mites drop and crawl across the page as moving specks. A hard jet of water rinses them from the foliage, horticultural oil clears a heavy run, and steady watering through the heat keeps the color from dulling in the first place.
Fix:
- Spray foliage with a strong jet of water to dislodge mites
- Treat heavy infestations with horticultural oil or miticide
Toxicity
Green Giant arborvitae is best kept off the menu, though a casual nibble of the foliage is more a stomach upset than an emergency. Those soft, scale-like leaves carry thujone, an oil that can irritate the stomach and skin of pets, livestock, and people. The real hazard is concentrated arborvitae essential oil, which should never be left where animals can reach it.
Toxic to
Cats · Dogs · Horses · Rabbits · Livestock · Birds · People
Cats Mild
A cat that chews the flat, scale-like foliage usually ends up drooling, with an upset stomach or a bout of diarrhea. The thujone oil held in the leaves is the cause, and a curious nibble is far milder than the concentrated essential oil.
Dogs Mild
A dog that mouths the soft green sprays tends to drool, throw up, or pass loose stools and go quiet for a while. It usually clears on its own, but the concentrated arborvitae oil belongs well out of reach.
Horses Mild
A horse that browses the bitter foliage may end up with a mild stomach upset. It sits on the list of plants to keep them from, though serious trouble from a casual taste is rare.
Rabbits Mild
The same thujone in the scale-like leaves that bothers cats and dogs can upset a rabbit's stomach, so keep it off the foliage. Its usual greens are the safer choice.
Livestock Mild
Cattle, goats, and sheep mostly turn away from the bitter, aromatic foliage, but a hungry animal that strips a branch can take on enough oil for some digestive upset. Fence stock off from young plantings.
Birds Caution
Birds tuck into the dense, layered branches for shelter without any harm. They do not treat the foliage as food, so the only real caution is keeping concentrated thuja oil away from them.
People Caution
No part of this plant is meant to be eaten, and the resinous leaves can irritate the stomach and skin. Wear gloves if the sap bothers you while shearing, and keep the concentrated essential oil away from children.
Keep pets from chewing foliage and never apply or leave out concentrated thuja/arborvitae essential oil around animals; oral exposure is the highest-risk route.
Helpline numbers
United States
ASPCA Animal Poison Control: (888) 426-4435 (fee applies)
Poison Control: (800) 222-1222
Canada
Poison Centres: 1-844-764-7669
Varieties
Green Giant is the largest of the popular arborvitae, and a few relatives cover the spots where its broad frame would be too much. These are the ones worth knowing by name.
'Emerald Green' ('Smaragd')
A far smaller Thuja occidentalis that holds around 10 to 15 feet tall and 3 to 4 feet wide, sized for tighter spots where the broad Green Giant would crowd everything out.
'Spring Grove'
Another fast, large pyramidal arborvitae grown the same way Green Giant is, rising as a quick privacy screen.
'American Pillar' (Thuja occidentalis 'Pillar')
A tall, tightly columnar form built for narrow vertical screens, far slimmer in outline than the broad-shouldered Green Giant.
How to propagate
There is only one practical way to make more Green Giants, since the plant sets no seed of its own.
Stem cuttingsModerate
Late summer to fall (semi-hardwood cuttings) · Several weeks to a few months to root
Because the cultivar is sterile and sets no seed, every Green Giant is struck from a cutting of that same soft, scale-like foliage. Take semi-hardwood cuttings in late summer or fall, then give them a few weeks to a few months to root before they are grown on.
Myths
Green Giant arborvitae stays a neat, compact shrub sized for a small hedge.
This is a fast-growing forest tree, not a foundation shrub. It climbs 40 to 60 feet tall and broadens 12 to 18 feet wide, a full pyramid that needs real room. Set it as a small hedge and it will swallow the space whole.
Arborvitae seeds itself around the landscape and becomes invasive.
As a sterile hybrid, 'Green Giant' produces no viable seed at all, which leaves it no route into surrounding wild ground. The tree holds its spot and goes nowhere.