Tree · Cupressaceae
Green Giant Arborvitae
Thuja 'Green Giant'
Give it full sun and room to spread, and this tree throws up a living privacy wall fast.
Full sun
Every 7–14 days
USDA 5–8
40–60 ft · 12.2–18.3 m
Overview
Need a tall, dense screen and don't want to wait around for it? Green Giant arborvitae is the plant people reach for. It's a hybrid evergreen in the cypress family, a cross of two Thuja species, and once it settles in it can tack on several feet of growth a year. Line a few up and they knit into a solid green wall that blocks wind, noise, and whatever the neighbors are up to.
Don't let the word arborvitae trick you into thinking small. This is a forest-scale tree that shoots up to 40 to 60 feet tall and fills out to 12 to 18 feet wide, with a narrow pyramid shape and soft, scale-like foliage that stays green all winter. The 'Green Giant' name? Totally earned. Give it the room it actually needs and it'll ask for almost nothing back.
What makes it so popular is that it's just plain tough and easy. It shrugs off most pests and disease, deer usually walk on by, and it puts up with all sorts of soils. The one thing it won't forgive is a soggy, poorly drained spot, and that's where root rot creeps in and can take the whole plant down.
Care
The short version: pop it in full sun in well-drained soil, leave it room to hit its full 40 to 60 feet, and keep it watered through the first couple of years while the roots settle in.
Light
Green Giant does best in full sun, where it stays nice and dense top to bottom. It'll put up with partial sun or light shade, but the more shade it sits in, the thinner and looser the foliage gets.
Water
Keep the soil moist for the first one to two years while the roots settle in, watering about every 7 to 14 days. After that it can coast through short dry spells, though steady moisture in well-drained soil is what really pushes the fastest growth.
Soil
It's not picky at all and takes clay, sand, and pretty much everything in between, as long as the ground drains. A moist, fertile, well-drained loam is its happy place, and it's fine across a wide pH range from 5.5 to 8.0.
Temperature
This is a seriously cold-hardy tree, comfortable from about -20°F to 100°F (-29°C to 38°C), which covers USDA zones 5 through 8. It holds its color through brutal winters, though a biting wind can scorch the foliage that's out in the open.
Humidity
Regular outdoor air suits it just fine, so there's no humidity number to fuss over. What matters more is good airflow between plants, because crowding traps moisture and invites trouble.
Feeding
In decent soil it barely needs feeding at all. If growth is looking weak, work in a balanced slow-release tree fertilizer in spring, but leave it be on plants that are already doing well.
Pruning
Green Giant needs little to no pruning and keeps its shape on its own. Shear it in late spring or early summer only if you're keeping it as a hedge, and tie up or pull out extra leaders so snow can't drag them apart.
Repotting
It's a landscape tree, not a container plant, so repotting barely ever comes up. While it's in a nursery pot, keep an eye out for roots circling or poking out the drainage holes, which is your cue to get it in the ground.
Size & spacing
Picture a grown tree at 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 width in mind. Skip that step and you'll wind up with crowded, oversized plants jammed up against the house and lines.
When to plant
It's grown for its evergreen foliage, so there's no flower or harvest to plan around. Just set new plants out in spring or fall, when the soil's easy to work and the weather's mild, and let that cooler stretch help the roots settle before summer heat or winter cold rolls in.
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 happy Green Giant hardly ever gives you grief, but when something does go sideways it usually shows up in the foliage or after a rough winter. Once you can tell winter burn from a pest, or a wet-site slump from plain drought stress, you'll catch it early. Find what matches below, then jump on it while it still makes a difference.
Whole tree going yellow and thin on soggy ground
When a plant on a wet, heavy spot starts fading all over, it's usually root rot, with Phytophthora getting in wherever the ground stays soggy. Dig down a little and the roots feel dark, soft, and mushy. There's no quick fix once it's in, so the smart move is to sort out the drainage, back off the watering, and pull out any badly hit plants so it can't creep to the rest.
Fix:
- Improve drainage and stop overwatering
- Avoid planting in low, waterlogged spots
- Remove severely affected plants to limit spread
Brown, crispy foliage showing up once winter's over
This is almost always winter burn, and it hits the side that takes the wind and sun the hardest. Here's what's going on: the foliage keeps losing water all winter, but the frozen roots can't send any back up, so the tissue dries out and bleaches instead of spotting. Give it a deep drink in fall before the ground freezes, mulch over the roots, and don't cut anything until spring growth shows you what 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
Thinning branches with little hanging bags on them
See those tiny bags? They're the handiwork of evergreen bagworm caterpillars, which munch the foliage and lug their cover around with them. They run 0.25 to 2 inches long and they're stitched together from bits of the plant, so scan the twigs for them dangling down. Just pick them off through fall and winter before the eggs hatch, and if young ones come back, a Bt spray in late spring sorts them out.
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 out or snapped after a snowfall
That skinny pyramid shape catches snow and ice, and all that weight can pry the leaders apart or crack them off. Brush the snow off before it settles and freezes, and tie the upright stems together with something soft so they hold their shape. And here's a tip: starting with a single-leader plant saves you most of this hassle down the line.
Fix:
- Gently brush snow off before it accumulates and freezes
- Tie multiple leaders together with soft material for support
- Prune cleanly broken branches
Dull, bronzy foliage with a bit of fine webbing
Hot, dry weather is when spider mites show up, and they suck the color right out of the foliage until it looks stippled and bronze. Want to be sure? Hold a piece of white paper under a branch, give it a tap, and watch for tiny specks scooting around. A good blast of water knocks most of them off, horticultural oil takes care of a bad run, and honestly, just keeping the tree watered through the heat is the easiest way to stay ahead of them.
Fix:
- Spray foliage with a strong jet of water to dislodge mites
- Treat heavy infestations with horticultural oil or miticide
Toxicity
It's best to keep Green Giant arborvitae off the menu, though a casual nibble is more of a stomach ache than an emergency. The foliage carries thujone, an oil that can irritate the stomach and skin of pets, livestock, and people. The thing to really watch is concentrated arborvitae essential oil, which should never be left where animals can get at it.
Toxic to
Cats · Dogs · Horses · Rabbits · Livestock · Birds · People
Cats Mild
If a cat grabs a nibble of the foliage, you'll usually just see some drooling, a queasy tummy, or a little diarrhea. That's the thujone oil in the leaves at work, and a curious taste is nowhere near as worrying as the concentrated essential oil would be.
Dogs Mild
A dog that chews on the foliage might drool, be sick, or get loose stools and seem a bit worn out for a while. It usually passes on its own, but it's smart to keep the concentrated arborvitae oil somewhere the dog can't get to it.
Horses Mild
A horse that browses the foliage could end up with a mild tummy ache, and not much more. It's on the list of plants to keep them away from, though a casual taste hardly ever turns into anything serious.
Rabbits Mild
That same thujone that bugs cats and dogs can upset a rabbit's stomach too, so it's best not to let it browse the foliage. Just stick with its usual greens and you're good.
Livestock Mild
Cattle, goats, and sheep tend to steer clear of the bitter foliage on their own, but a hungry one that strips a branch might get a bit of digestive upset from the oils. A simple fence around young plantings keeps them out of trouble.
Birds Caution
Birds are happy to shelter in the thick branches, and it doesn't hurt them at all. They're not going to go looking to eat the foliage, so really the only thing to watch is keeping any concentrated thuja oil away from them.
People Caution
No part of this plant is meant to be eaten, and the leaves can leave your stomach and skin irritated. Pop on some gloves if the sap bugs you while shearing, and keep that concentrated essential oil away from the kids.
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's the biggest of the popular arborvitae, but a handful of relatives step in for the spots where it'd just be too much tree. Here are the ones worth knowing by name.
'Emerald Green' ('Smaragd')
If Green Giant's too big for the spot, this smaller Thuja occidentalis settles in around 10 to 15 feet tall and 3 to 4 feet wide, which is perfect for tighter corners.
'Spring Grove'
You grow this one just like Green Giant, another fast, big pyramidal arborvitae that makes a quick privacy screen.
'American Pillar' (Thuja occidentalis 'Pillar')
When all you've got is a narrow vertical gap, this slim column slots right in, way skinnier than the broad-shouldered Green Giant.
How to propagate
There's really only one practical way to make more Green Giants, since the plant doesn't set any seed of its own.
Stem cuttingsModerate
Late summer to fall (semi-hardwood cuttings) · Several weeks to a few months to root
Since this cultivar's sterile and there's no seed to sow, every single Green Giant starts life as a cutting. Take semi-hardwood cuttings in late summer or fall, and just give them a few weeks to a few months to root before you grow them on.
Myths
Green Giant arborvitae stays a tidy little hedge plant.
It's easy to think that, but this is really a fast-growing forest tree, not a foundation shrub. It gets to 40 to 60 feet tall and 12 to 18 feet wide, so it needs actual room. Try to squeeze it in as a small hedge and it'll just take over the whole space.
Arborvitae will spread and turn invasive.
No need to worry about that one. 'Green Giant' is a sterile hybrid, so it doesn't set any viable seed and it's got no way to escape into the wild. It stays right where you put it.