Tree · Cupressaceae
Green Giant Arborvitae
Thuja 'Green Giant'
Give it full sun and plenty of elbow room, and this easygoing tree grows you a living privacy wall before you know it.
Full sun
Every 7–14 days
USDA 5–8
40–60 ft · 12.2–18.3 m
Overview
If you're hoping for a tall, dense screen and don't want to wait years for it, Green Giant arborvitae is a wonderfully forgiving place to start. It's a hybrid evergreen in the cypress family, a cross between two Thuja species, and once it settles in it can add several feet of height a year. Line a few up and they knit together into a solid green wall that softens wind, muffles noise, and tucks away the view next door.
The word arborvitae sounds cozy, so it's worth knowing this is a genuine forest-scale tree that climbs 40 to 60 feet tall and reaches 12 to 18 feet wide, wearing a narrow pyramid shape and soft, scale-like foliage that stays green all winter long. The 'Green Giant' name really is earned. Give it the room it truly wants and it will ask almost nothing of you in return, which makes it a kind plant to learn on.
Part of why so many gardeners love it is how tough and easy it is to please. It brushes off most pests and diseases, deer usually walk right past it, and it copes with a wide range of soils without complaint. The one thing it can't quite recover from is a soggy, poorly drained spot, where root rot takes hold, so pick a well-drained home and you've cleared the biggest hurdle.
Care
The short version: give it full sun and well-drained soil, leave enough room for it to reach a full 40 to 60 feet, and keep it watered through the first couple of years while its roots settle in, and you'll do just fine.
Light
Green Giant is happiest in full sun, which keeps it lush and dense from the ground right up to the tip. It'll get by in partial sun or light shade too, but keep in mind that the shadier its spot, the thinner and looser the foliage tends to grow.
Water
Aim to keep the soil moist for that first one to two years while the roots find their feet, watering about every 7 to 14 days. Once it's established, it can shrug off a short dry spell, though steady moisture in well-drained soil is what fuels its fastest growth.
Soil
You don't need to fuss over the soil here, since it happily takes clay, sand, and most things in between, as long as the ground drains. A moist, fertile, well-drained loam is its favorite, and it's comfortable across a wide pH range of 5.5 to 8.0.
Temperature
This is a wonderfully cold-hardy tree, at ease anywhere from about -20°F to 100°F (-29°C to 38°C), which covers USDA zones 5 through 8. It keeps its color through hard winters, though sharp wind can scorch the foliage that's left exposed.
Humidity
Ordinary outdoor air is all it needs, so there's no humidity number to chase and one less thing to worry about. What matters more is good airflow between plants, because crowding traps moisture and invites problems.
Feeding
In reasonable soil it rarely needs feeding, so don't feel you have to. If the growth looks weak, work a balanced slow-release tree fertilizer into the soil in spring, but leave well enough alone on plants that are already thriving.
Pruning
Green Giant needs little to no pruning and keeps its shape all on its own, which is a relief. Shear it in late spring or early summer only if you're training it as a hedge, and tie up or remove any extra leaders so snow can't drag them apart.
Repotting
This is a landscape tree rather than a pot plant, so repotting hardly ever comes up. While it's still in a nursery pot, keep an eye out for roots circling or pushing through the drainage holes, your gentle cue that it's ready for 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. Give it that room now and you'll spare yourself crowded, oversized plants pressed up against the house and lines later.
When to plant
Because it's grown for its evergreen foliage rather than flowers or fruit, there's no bloom or harvest for you to time. Set new plants out in spring or fall, while the soil is easy to work and the weather stays mild, and let that gentler season help the roots settle 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 happy Green Giant rarely asks much of you, and the few troubles it does run into tend to surface in the foliage or after a rough winter. Once you can tell winter burn from a pest, or a wet-site decline from simple drought stress, you'll feel confident stepping in early. Find what matches below, then act while it still makes a difference.
Whole tree fading, yellow and thin, on a soggy spot
When a plant on wet, heavy ground starts fading all over, the culprit is usually root rot, often Phytophthora getting a foothold in ground that stays too wet. If you dig gently, the roots will feel dark, soft, and mushy. This one is hard to reverse once it takes hold, so the kindest thing you can do is improve the drainage, ease off the watering, and remove any badly hit plants so it can't travel.
Fix:
- Improve drainage and stop overwatering
- Avoid planting in low, waterlogged spots
- Remove severely affected plants to limit spread
Foliage turning brown and crispy once the hard winter passes
Take heart, this is almost always winter burn, and it lands hardest on the side that faces the wind and sun. The leaves keep releasing water even while the frozen roots have none to send up, so the tissue dries and pales instead of forming spots. Give it a deep drink in fall before the ground locks up, tuck mulch over the roots, and let fresh spring growth show you what came through before you trim a thing.
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 carrying small spindle-shaped bags
Don't panic if you spot these little bags, they belong to evergreen bagworm caterpillars that eat the foliage and haul their cover along wherever they go. Each one runs 0.25 to 2 inches long and is stitched from bits of the plant itself, so look for them dangling from the twigs. You can simply pluck them off through fall and winter before the eggs hatch, and if young ones return, a Bt spray in late spring puts you back in control.
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 pulled open or snapped after heavy snow
That slim pyramid shape catches snow and ice, and the load can pry multiple leaders apart or snap them off. The good news is it's easy to prevent: sweep snow off before it settles and freezes, and gently bind the upright stems together with soft ties so they keep their form. Starting with a single-leader plant saves you most of this worry down the road.
Fix:
- Gently brush snow off before it accumulates and freezes
- Tie multiple leaders together with soft material for support
- Prune cleanly broken branches
Dull, bronzed foliage laced with fine webbing
Long hot, dry stretches can bring on spider mites, tiny feeders that drain the color and leave the foliage flecked and bronze. To be sure, hold a sheet of white paper under a branch, tap it, and watch for specks moving across the page. A firm spray of water washes most of them off, horticultural oil settles a heavy 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 kindest to keep Green Giant arborvitae off the menu, though a curious nibble is far more likely to mean a sore stomach than a crisis. The foliage holds thujone, an oil that can irritate the stomach and skin of pets, livestock, and people alike. The one thing to take seriously is concentrated arborvitae essential oil, which should never be left anywhere animals can reach it.
Toxic to
Cats · Dogs · Horses · Rabbits · Livestock · Birds · People
Cats Mild
If a cat sneaks a nibble of the foliage, you'll most likely just see some drooling, a queasy stomach, or a little diarrhea. The thujone oil in the leaves is behind it, so a curious taste is far gentler than the concentrated essential oil would be.
Dogs Mild
A dog that chews the foliage may drool, be sick, or get loose stools and seem a bit tired for a while. It usually settles on its own, and you can rest easier by keeping the concentrated arborvitae oil somewhere out of reach.
Horses Mild
A horse that browses the foliage might get a mild stomach upset, nothing more in most cases. It's noted as a plant to keep them away from, though a casual taste rarely leads to real trouble.
Rabbits Mild
The same thujone that unsettles cats and dogs can give a rabbit a sore tummy, so it's best not to let it browse the foliage. Offer its usual greens instead and you'll both be happier.
Livestock Mild
Cattle, goats, and sheep usually pass over the bitter foliage on their own, but a hungry animal that strips a branch might get a little digestive upset from the oils. A simple fence around young plantings keeps everyone comfortable.
Birds Caution
Birds nest and shelter contentedly in the thick branches with no harm at all. They wouldn't seek out the foliage as food, so the one thing to watch is keeping any concentrated thuja oil away from them.
People Caution
No part of this plant is meant for eating, and the leaves can leave the stomach and skin irritated. Slip on gloves if the sap bothers you while shearing, and keep the concentrated essential oil well away from little ones.
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 biggest of the popular arborvitae, and happily a few close relatives fill the spots where it would simply be too large. Here are the ones worth getting to know by name.
'Emerald Green' ('Smaragd')
If Green Giant feels too big for your space, this daintier Thuja occidentalis settles in around 10 to 15 feet tall and 3 to 4 feet wide, perfect for a snug corner.
'Spring Grove'
You'll find this one grown just like Green Giant, another quick, large pyramidal arborvitae that makes a fast privacy screen.
'American Pillar' (Thuja occidentalis 'Pillar')
When you only have a slim vertical gap to fill, this narrow column fits beautifully, far more slender than the broad-shouldered Green Giant.
How to propagate
There's really just one practical way to grow more Green Giants, and the good news is it's straightforward once you know the trick, since the plant makes no seed of its own.
Stem cuttingsModerate
Late summer to fall (semi-hardwood cuttings) · Several weeks to a few months to root
Since this cultivar is sterile and gives you no seed to sow, every Green Giant begins as a cutting, and that's easier than it sounds. Take semi-hardwood cuttings in late summer or fall, then be patient and give them a few weeks to a few months to root before you grow them on.
Myths
Green Giant arborvitae stays a small, tidy hedge plant.
It's easy to assume so, but this is a fast-growing forest tree rather than a little foundation shrub. It reaches 40 to 60 feet tall and 12 to 18 feet wide, so give it honest room from the start. Treat it as a small hedge and it will simply outgrow the whole space.
Arborvitae will spread and become invasive.
You can relax on this one. 'Green Giant' is a sterile hybrid, so it makes no viable seed and has no path into the wild. It stays right where you put it.