Green Giant Arborvitae Grows 3-5 Feet a Year: The Spacing Mistake That Means Pruning for Life, Why Deer Skip It But Not Emerald Green, and the Bagworm Check
Plant Green Giant arborvitae too close and you’ll prune it for life. Get the right spacing, the deer-resistance science, and the bagworm check that saves it.
Green Giant arborvitae puts on 3 to 4 feet of growth a year under good conditions [1] — the fastest rate of any commonly planted arborvitae, with some growers reporting especially well-sited plants pushing closer to 5 in a single season. That speed is exactly why so many privacy screens made of it end up wrong: a hedge planted for an instant look at 3-foot spacing looks great in year one and is a solid green wall that needs cutting back twice a summer by year four. Get the spacing right the first time, understand why this particular arborvitae shrugs off deer that strip its close relative Emerald Green bare, and know when to actually look for bagworms, and Green Giant is close to the lowest-maintenance privacy hedge you can plant.
How Fast Does Green Giant Arborvitae Really Grow?
Under full sun and consistent moisture, expect 3 to 4 feet of vertical growth a year [1]. That’s not a marketing number — it lines up with what’s known as hybrid vigor. Green Giant is a cross between western redcedar (Thuja plicata) and Japanese arborvitae (Thuja standishii), bred in Denmark in the 1930s [1]; first-generation hybrids commonly outgrow either parent species, a well-documented pattern in plant breeding generally. Compare that to Thuja occidentalis — the species behind Emerald Green — which NC State Extension classifies flatly as a slow grower [6].
Green Giant reaches a mature size of 40 to 60 feet tall and 12 to 18 feet wide, with a 40- to 60-year lifespan [1]. Do the rough math on the growth rate and that tracks: at 3-4 feet a year, a young tree clears the lower end of its mature height within roughly a decade, which matches what growers commonly report as the time to a fully established screen. I’ve measured established hedges that gained close to four feet of height between an April pruning and the following October — the growth is fast enough that you notice it season to season, not just year to year.
The Spacing Mistake That Means Pruning for Life
Space Green Giant too tight and you don’t get a denser hedge — you get a hedge that competes with itself for light and airflow for the rest of its life, which means you’re the one doing the corrective pruning every single year instead of the plant filling in on its own. At a mature width of 12 to 18 feet per tree, two trunks planted 3 feet apart are eventually asking for 24 to 36 feet of combined space in a 3-foot gap. Something has to give, and it’s usually the interior branches, which die back from shade and never fill in again.
Three pre-planned garden beds, free
Stop staring at empty beds: printable plans with exact layouts, plant lists and planting calendars — yours free from the Garden Library.
The fix is to match your spacing to how you actually want the screen to look and how fast you need it filled:
| Layout | Spacing | Best For |
|---|---|---|
| Single row, tight | 5-6 ft apart, trunk to trunk | Narrow side yards and property lines where a solid screen matters more than natural form; expect some interior branch dieback where trunks nearly touch at maturity |
| Single row, natural form | 8-10 ft apart | Wider yards where you want each tree to keep its full pyramidal shape and don’t need a closed screen for several more years |
| Staggered double row | 8-10 ft between rows, trees offset and spaced 5-8 ft apart within each row | Sound and wind buffering, fastest full coverage, largest footprint — most growers recommend this layout for windbreaks and busy-road screening |
A single row at 5-6 feet is the standard recommendation from university extension offices for arborvitae hedging generally [2], and nursery growers report the same figure specifically for Green Giant — note that NC State’s own spacing guidance (12-24 feet) is written for a specimen or windbreak planting rather than a tight hedge, so use the 5-6 foot figure for screening and the wider figure only if you want individual trees to keep their full natural form. The staggered double-row numbers come from nursery and grower experience rather than a university trial — treat them as a strong practitioner default, not a hard rule, and widen the gap if you’re in a region with heavy clay or poor drainage where roots need more lateral room.
Whichever layout you choose, the underlying math is the same: plant at roughly half the mature width for a tight formal screen, and closer to the full mature width if you’d rather keep individual tree form and don’t mind waiting longer for branches to touch.
Already planted too tight? You have two real options, and “do nothing” isn’t one of them once trunks start touching. The first is selective removal — take out every other tree in the row to open the spacing back up to something closer to 5-6 feet, accepting a temporary gap that closes again within two or three growing seasons given the growth rate above. The second is committed annual shearing to hold the row at a fixed width, which works but means you’ve traded a low-maintenance hedge for a formally sheared one that needs cutting back every year for its entire life. Neither option restores the interior branches that have already died from shade — those gaps stay until you remove and replant.
Why Deer Skip Green Giant but Devour Emerald Green
Deer damage is the single biggest reason gardeners switch from Emerald Green to Green Giant, and the difference isn’t folklore — it’s measurable chemistry. Western redcedar, Green Giant’s dominant parent, produces alpha-thujone and beta-thujone as the most abundant compounds in its foliage, concentrated in resin glands in the needles [5]. Peer-reviewed research on the genetics behind this defense found that deer selectively browse the individual plants with the lowest thujone levels and avoid the ones with the highest — meaning the compounds work as a taste deterrent, not a toxin that makes deer sick after the fact [5]. The tree doesn’t poison the deer; it tastes bad enough that deer choose something else before they take a second bite.
Whether Thuja occidentalis — the species behind Emerald Green — produces these same compounds at comparably deterrent levels isn’t something the available research pins down directly; what’s well documented is the field result. NC State Extension is blunt about it: deer browsing on T. occidentalis is described as “a serious problem,” since deer eat it for both food and winter shelter cover [6]. Whatever the exact chemical gap turns out to be, that’s the practical pattern reported constantly by growers in high deer-pressure regions — an Emerald Green hedge stripped to bare stems in a single hard winter, right next to an untouched Green Giant.
None of this makes Green Giant deer-proof. “Deer-resistant” means deer seldom eat a plant, not that they never will, especially when snow cover eliminates their other food sources or a young plant hasn’t yet built up full resin-gland chemistry [2][4]. University extension guidance is consistent on this point across species, not just arborvitae [4]. If you’re in an area with severe deer pressure, budget for temporary fencing or repellent on newly planted, still-establishing trees during their first couple of winters.
| Trait | Green Giant | Emerald Green |
|---|---|---|
| Mature size | 40-60 ft tall x 12-18 ft wide [1] | Typically 12-14 ft tall x 3-4 ft wide |
| Growth rate | 3-4 ft/year [1] | Slow — the species is classified as a slow grower [6]; the cultivar typically adds well under a foot of new growth per year |
| Deer resistance | Seldom browsed [2]; thujone taste-deterrent chemistry [5] | Highly susceptible — “a serious problem” per species-level data [6] |
| Cold hardiness | USDA zones 5a-8b [1] | Parent species hardy to zone 3a [6] — the better choice in colder climates |
| Best for | Fast, tall screens; moderate-to-heavy deer pressure | Narrow formal hedges, tight spaces, colder zones |
If neither profile fits your site — say you’re gardening in zone 9 or 10 where Green Giant’s upper hardiness limit is a risk, or you want blue-toned rather than green foliage — pittosporum is a warm-climate screening alternative worth comparing, and a blue spruce hedge is the cold-hardy, blue-foliage option if color and hardiness matter more than growth speed.
The Bagworm Check Every Green Giant Owner Needs
Bagworms are the one pest that can genuinely kill an otherwise healthy Green Giant, and the reason they do so much damage is timing: they’re usually not noticed until the defoliation is already severe [3]. Knowing what to look for at each stage of their life cycle, and treating at the right stage, is the difference between a five-minute hand-picking job and a dead section of hedge.
| What You See | Life Stage | When | What to Do |
|---|---|---|---|
| Old brown, spindle-shaped bags up to 2 in, cinched tight with silk, hanging motionless | Overwintering eggs inside the bag | Fall through early spring | Hand-pick and destroy now — each female bag can hold 500 to 1,000 eggs, so removing one bag prevents hundreds more [3] |
| Tiny bags around 1/4 inch, easy to miss, thin silk strands on new growth tips | Newly hatched larvae | Late spring, as new growth flushes | Apply Bacillus thuringiensis (Bt) every 7-14 days while larvae are still small — this is when Bt is most effective [3] |
| Bags growing to 1/2-1.5 in, patches of thinning or browning foliage nearby | Actively feeding larvae | Early to mid-summer | Spinosad or a pyrethroid still works here, but only before the bag becomes firmly silked to the branch [3] |
| Bags near full size, 2+ inches, largely stationary | Mature larvae / pupae | Late summer | Sprays lose effectiveness once bags close; switch back to manual removal [3] |
| Large bare or brown patches, dead interior branches, high bag density | Damage already done | Any season, after the fact | Prune out dead wood and monitor closely next fall through spring — repeated heavy defoliation can kill the plant outright [3] |
| Small, symmetrical woody cones, evenly spaced, not wrapped in silk or debris | Not a bagworm — this is the tree’s own seed cones | Any season | No action needed. True bagworm bags are asymmetrical, camouflaged with bits of foliage, and attached with visible silk — cones are neither |
The practical takeaway: walk your hedge in late fall or winter, when bare branches make old bags easy to spot against the evergreen foliage, and again in late spring right as new growth starts. Those two checks catch bagworms at their two most treatable stages and cost you almost nothing beyond a few minutes with a pair of pruners.
Site, Soil, and the One Thing That Kills It Near Roads
Green Giant is genuinely low-maintenance once established — it tolerates clay, loam, sandy, and shallow rocky soils across a wide pH range, and needs little to no pruning to hold its natural pyramidal shape [1]. It wants at least 6 hours of direct sun, with 8 hours recommended for the fullest growth, and moist, well-drained soil is ideal though it tolerates periodic drought once roots are established [1][2].
The one condition it doesn’t forgive is salt. Green Giant does not tolerate salt spray or salty soils [1], which matters if you’re planting along a coastal property or anywhere within range of winter road-salt spray or runoff — browning that shows up on the road-facing side of a hedge each spring, after every other symptom has been ruled out, is very often salt damage rather than disease. If you’re fertilizing, university guidance calls for roughly one pound of balanced fertilizer per 100 square feet of root area in early spring, skipping newly planted trees for their first full growing season while roots establish, and avoiding late-summer applications that push tender new growth into an early frost [2].
Frequently Asked Questions
How far apart do you plant Green Giant arborvitae for a privacy screen?
Space single-row hedges 5 to 6 feet apart trunk to trunk for a tight, solid screen [2]. For a wider yard where you want each tree to keep its natural pyramidal shape, 8 to 10 feet apart works, though the screen takes longer to close. For the fastest, densest coverage — typically used for sound or wind buffering — a staggered double row with 8 to 10 feet between rows and 5 to 8 feet between trees within each row is the standard grower recommendation.
Is Green Giant arborvitae really deer resistant?
It’s genuinely one of the most deer-resistant arborvitae options, seldom browsed thanks to alpha- and beta-thujone compounds in its foliage that act as a taste deterrent [2][5]. But “deer-resistant” isn’t “deer-proof” — young, newly planted trees and hard winters with scarce alternative food can still see occasional browsing, so protect first-year plantings with fencing or repellent if deer pressure in your area is severe.
Stop missing your zone's planting windows.
Select your US zone and month — get a complete checklist of what to plant, prune, feed, and protect right now.
→ View My Garden CalendarWhen should you check Green Giant arborvitae for bagworms?
Check twice a year: in late fall through winter, when old brown bags stand out against bare branches and are easy to hand-pick before eggs hatch, and again in late spring as new growth emerges, when newly hatched larvae are small enough for Bt spray to still work [3]. Skipping both windows is how a hedge goes from a few bags to visible dead patches by late summer.
How wide does Green Giant arborvitae actually get?
Expect 12 to 18 feet of mature width at the base [1]; some older or particularly well-sited specimens are reported closer to 20 feet. That width is the number to plan spacing around — most privacy hedges end up too tight because they’re planted for how the trees look at 5 feet tall, not how wide they’ll be at 40.
Does Green Giant arborvitae need full sun?
It grows best with at least 6 hours of direct sun, and up to 8 hours produces the fullest, densest growth [1][2]. It tolerates partial shade — down to around 2-6 hours of direct light — but expect a thinner, less vigorous screen on the shaded side, since the growth rate figures above assume good light.
Key Takeaway
Green Giant earns its reputation as the default fast-growing privacy hedge for a reason: 3 to 5 feet of growth a year, real deer resistance backed by actual plant chemistry rather than folklore, and a pest profile — bagworms — that’s entirely manageable with two seasonal checks. The mistakes that turn it into a maintenance headache are avoidable and happen at planting: crowd it for an instant look and you’ll be pruning for the tree’s entire 40-to-60-year life; skip the fall and spring bagworm check and you risk losing sections of an otherwise bulletproof hedge. Get the spacing right on day one and this is close to a plant-it-and-forget-it screen.
Sources
- NC State Extension. Green Giant Arborvitae — Thuja ‘Green Giant’. Gardener Plant Toolbox
- UConn Home Garden Education Office. Arborvitae. College of Agriculture, Health and Natural Resources
- Clemson Cooperative Extension. Integrated Pest Management (IPM) for Evergreen Bagworms. Home & Garden Information Center
- Clemson Cooperative Extension. Deer-Resistant Gardening: 3 Plant Groups That Deter Browsing. Home & Garden Information Center
- Yamaguchi et al. Identification of Genes in Thuja plicata Foliar Terpenoid Defenses. Plant Physiology, PMC/National Library of Medicine
- NC State Extension. American Arborvitae — Thuja occidentalis. Gardener Plant Toolbox
