Green Giant Arborvitae: The Fast-Growing Privacy Tree That Replaced Leyland Cypress

Green Giant Arborvitae grows 3-5 feet per year, shrugs off deer, resists the diseases that killed millions of Leyland Cypress trees, and stays green all winter. It earned the Pennsylvania Horticultural Society Gold Medal in 1998 and hasn’t slowed down since. If you’re shopping for a privacy screen, this tree will be on every list.

But Green Giant gets big. We’re talking 40-60 feet tall and 12-20 feet wide at maturity. That’s a serious tree, not a hedge plant. Too many homeowners plant a row of these 5 feet from the fence and spend the next decade fighting with loppers. Here’s what you actually need to know before buying.

Quick-reference profile:

• Botanical name: Thuja (standishii x plicata) ‘Green Giant’
• Mature size: 40-60 feet tall, 12-20 feet wide
• Growth rate: 3-5 feet per year (very fast)
• Zones: 5a-8b
• Sun: Full sun (6+ hours direct)
• Soil: Moist, well-drained, pH 6.0-8.0
• Deer resistant: Yes (seldom browsed)
• Cost: $35-80 per tree depending on size

Where Green Giant comes from

Green Giant is a hybrid between Western Red Cedar (Thuja plicata, native to the Pacific Northwest) and Japanese Arborvitae (Thuja standishii, native to Japan). That combination gives you the vigor and size of Western Red Cedar with the cold hardiness and tighter habit of the Japanese parent.

The original seedling was discovered in 1937 by nurseryman D.T. Poulsen at his family nursery in Kvistgaard, Denmark. In 1967, Poulsen sent a single specimen to the U.S. National Arboretum in Washington, D.C. That one tree grew so fast and looked so good that researchers started propagating it for evaluation.

The identity got confused along the way. The clone was mixed up with another arborvitae from the same Danish nursery, and it took detective work by Susan Martin at the National Arboretum, Kim Tripp at the New York Botanical Garden, and Robert Marquard at Holden Arboretum to sort it all out through records searches and isozyme analysis. The name “Thuja ‘Green Giant’” was officially chosen to identify the correct clone, according to the University of Arkansas Extension’s Plant of the Week profile.

Growth rate and mature size

This is where Green Giant separates itself from every other arborvitae.

Young trees put on 3-4 feet of growth per year under good conditions. Some trees have reached 50 feet tall within 10 years under optimal conditions.

Real-world timeline from a 5-6 foot nursery tree:

• Year 1: 5-6 feet (what you planted)
• Year 3: 12-16 feet
• Year 5: 18-24 feet
• Year 10: 30-40 feet
• Year 15+: 40-50 feet

These trees probably top out at around 60 feet with a basal spread of 15-20 feet. That’s two to three times the size most homeowners imagine when they buy a 6-foot tree at the nursery.

Growth rate slows with maturity. The fastest years are 3-10 after planting. By year 15-20, annual growth drops to 1-2 feet as the tree approaches its mature dimensions.

Why everyone switched from Leyland Cypress

Leyland Cypress dominated the privacy tree market from the 1980s through the early 2000s. Then Seiridium canker and Botryosphaeria canker started tearing through plantings across the Southeast. Entire rows of Leylands turned brown and died within a single season. Green Giant resists both of those canker diseases, which is why it became the go-to replacement.

Green Giant resists both of those canker diseases. It also tolerates ice and snow loads better than Leyland (which has notoriously shallow roots and tends to topple), handles cold down to -20 degrees F, and doesn’t require the constant pruning that Leylands need to stay shaped.

The one advantage Leyland Cypress still holds: it grows in hotter climates (Zones 6-10) while Green Giant tops out at Zone 8b.

How to plant a Green Giant privacy screen

Spacing math

This is the most important decision you’ll make. Get it wrong and you’ll be pruning every other month or watching trees compete and die.

• Dense privacy screen: 5-6 feet apart, center to center. Branches touch within 2-3 years and form a solid wall.
• Standard screen with breathing room: 6-8 feet apart. Fills in by year 4-5, easier to maintain long-term.
• Staggered double row: Rows 8-10 feet apart with 5-8 feet between trees in each row. Creates a thicker barrier faster and looks more natural.
• Windbreak: 8-12 feet apart. Maximum wind protection, less visual density.

Distance from structures: Plant at least 10 feet from foundations, retaining walls, and septic systems. Give 6-8 feet of clearance from fences. These trees spread 12-20 feet at the base, and planting too close means you’ll be pruning the bottom third for the life of the tree.

Planting technique

Dig the hole three times as wide as the root ball but only as deep. Set the root flare at or slightly above grade. Backfill with native soil (no need to amend unless your soil is pure clay), tamp down to eliminate air pockets, and water deeply. Lay 2-3 inches of mulch in a wide ring around the base, keeping it 4 inches away from the trunk.

Proper planting depth is critical for long-term survival. Buried root flares lead to crown rot, the same problem that kills Emerald Green Arborvitae.

Best timing: Plant in spring (after last frost) or fall (September-October). Avoid summer heat stress. Fall planting lets roots establish before winter dormancy kicks in. For step-by-step planting technique, see our bare root planting guide.

Year-round care schedule

Watering

First two weeks: Water every other day with a soaker hose or drip line. Soak the entire root zone.

First growing season (weeks 3-16): Water deeply once or twice per week. The goal is consistent moisture, not daily sprinkling. Use drip irrigation or soaker hoses rather than sprinklers for all arborvitae.

Years 1-2: Weekly deep watering during dry stretches. Don’t rely on lawn sprinklers reaching the root zone.

Established trees (year 3+): About 1 inch of water per week from rain or irrigation. Green Giant tolerates periodic drought once established, but prolonged dry spells cause interior browning and slow growth.

Critical fall watering: Water deeply in late fall before the ground freezes. Winter desiccation (browning from cold, dry winds) happens when frozen soil can’t supply moisture to foliage that’s still losing water. This is the number one cause of winter browning on otherwise healthy trees.

Fertilizing

One application per year, in early spring before new growth starts. Use a slow-release granular fertilizer high in nitrogen. NPK ratios of 10-5-5, 10-10-10, or 16-5-9 all work. Spread 1 pound per 100 square feet across the root zone.

Stop fertilizing after early summer. Late fertilizing pushes tender new growth that gets burned by the first frost. Check our spring tree care guide for a full seasonal maintenance schedule.

Pruning

Green Giant’s natural pyramidal shape looks good without any pruning at all. That said, here’s what you can do:

• Height control: Remove up to one-third of the central leader in late winter. This slows vertical growth but won’t stop it permanently.
• Width trimming: Cut branches back up to one-third of their length before the spring growth flush.
• Hedge shearing: Annual light shearing in late winter or early summer. For formal hedges, shear twice per year.
• Never cut into bare wood. Arborvitae will NOT regenerate from old, leafless stems. If you cut back to bare branches, those spots stay bare forever. This is the most important pruning rule for any arborvitae. See our pruning timing guide for details.

Maximum removal: no more than one-third of the tree per season.

Pest and disease management

Green Giant has genuinely excellent pest and disease resistance. It shrugs off most diseases, insects, periodic droughts, and deer. But “resistant” doesn’t mean immune.

Bagworms: the real threat

Bagworms are the most significant pest for any arborvitae, including Green Giant. The caterpillars build distinctive 1-2 inch brown cocoons that hang from branches like ornaments. Heavy infestations strip foliage and kill trees. Arborvitae is one of bagworms’ favorite hosts.

What to do: Hand-pick bags in winter (each female bag contains 500-1,000 eggs). For active infestations, apply Bacillus thuringiensis (Bt) when caterpillars are young and actively feeding, typically late May through mid-June. Bt is organic and doesn’t harm beneficial insects.

Spider mites

Spruce spider mites thrive in hot, dry conditions. Look for fine yellow stippling on foliage that progresses to bronze with tiny webbing. Treatment: strong water spray to dislodge, followed by horticultural oil or insecticidal soap if needed. Avoid broad-spectrum insecticides that kill the predatory mites keeping populations in check.

Root rot (Phytophthora)

The number one killer of Green Giant. It’s caused by water molds in waterlogged soil. The tree yellows from the base up, declines rapidly, and dies. Prevention is everything: plant in well-drained soil, don’t overwater, and don’t pile mulch against the trunk.

If your soil stays soggy after rain, either amend with gravel and organic matter for drainage or choose a different planting location. No amount of fungicide saves a tree sitting in wet soil.

Green Giant vs Emerald Green vs Leyland Cypress

This is the comparison that matters for most homeowners shopping for privacy trees.

Feature	Green Giant	Emerald Green	Leyland Cypress
Growth rate	3-5 ft/year	6-12 in/year	3-4 ft/year
Mature height	40-60 ft	12-15 ft	60-70 ft
Mature width	12-20 ft	3-4 ft	10-15 ft
Zones	5-8	3-7	6-10
Deer resistance	Good	Poor	Moderate
Disease resistance	Excellent	Moderate	Poor
Wind/ice tolerance	Good	Fair (splays)	Poor (topples)
Pruning needed	Low	Minimal	High
Best for	Large screens	Small spaces/hedges	Warm climates only

Bottom line: Green Giant is the best all-around privacy tree for yards with room. Emerald Green Arborvitae wins for tight spaces and cold climates (Zone 3). Leyland Cypress is only worth planting in Zone 9-10 where Green Giant can’t survive.

The monoculture warning

Extension services across the country are sounding the alarm about Green Giant monocultures. The warning is simple: don’t plant solid rows of any single species, including Green Giant.

Remember what happened with Leyland Cypress. Millions of identical trees planted coast to coast. One disease showed up and wiped them out by the neighborhood. Green Giant is more disease-resistant today, but planting another monoculture is rolling the same dice.

What to do instead: Mix Green Giant with other evergreens in your screen. Our evergreen trees guide profiles the best species for mixed screens. Plant Cryptomeria, Holly, or Eastern Red Cedar between every third or fourth Green Giant. The screen looks more natural, provides habitat diversity, and protects against any single pest or disease taking out your entire privacy barrier. Our columnar evergreen trees guide covers narrow options that fit well in mixed screens.

Honest assessment for California yards

I’ll be direct: Green Giant works in Northern California (Sacramento, Bay Area) but it’s not the slam-dunk it is back East. Zone 9a and warmer push the limits of its heat tolerance. It does not appreciate intense afternoon sunlight in hot climates.

In Sacramento’s zone 9b, Green Giant grows but slower than advertised, especially during July-September heat. You’ll get 2-3 feet per year instead of 4-5. Plant on the north or east side of the property where it gets morning sun and afternoon shade. Water more frequently than the general guidelines suggest.

For truly hot inland valleys, Italian Cypress or Deodar Cedar might serve you better. Native and Mediterranean-adapted species are a smarter fit for Central Valley landscapes. The Sacramento Tree Foundation offers free shade tree programs worth checking out if you’re planting for energy savings.

Frequently asked questions

How far apart should I plant Green Giant arborvitae? For a solid privacy screen, plant 5-6 feet apart center to center. For a looser screen with less maintenance, go 6-8 feet apart. A staggered double row with 8-10 feet between rows creates the thickest barrier.

Can I keep Green Giant arborvitae small? You can slow it down with annual pruning, but you cannot permanently keep a 50-foot tree at 10 feet. If you want a 10-15 foot hedge, plant Emerald Green Arborvitae or North Pole arborvitae instead. Fighting a tree’s genetics is a losing battle.

Do deer eat Green Giant arborvitae? Rarely. The Western Red Cedar parentage gives Green Giant aromatic oils that deer find unpalatable. It’s seldom browsed. Young trees may need temporary protection in areas with heavy deer pressure, but established Green Giants are generally left alone.

Why is my Green Giant turning brown? Four common causes: transplant shock (recovers within one season), overwatering or underwatering, winter desiccation (water deeply in fall), or tip blight fungus (stress-related, improve growing conditions). Interior browning in autumn is normal shedding. See our guide on how to tell if a tree is dead for diagnosis tips.

How long does Green Giant arborvitae live? With proper siting and care, Green Giant can live 40-60 years or more. That’s significantly longer than Leyland Cypress, which often declines after 20-25 years due to disease susceptibility.

Is Green Giant arborvitae invasive? No. The root system is shallow and fibrous, spreading about as wide as the canopy but only 18-24 inches deep. Roots will not damage foundations, sidewalks, or sewer lines. Plant at least 10 feet from structures to allow for the mature base spread.