How to Trim Arborvitae

Trim arborvitae in late spring or early summer, after new growth hardens off, and cut only into areas with active green foliage. Cutting into brown dead zones creates bare patches that will never regrow.

Arborvitae is one of the most forgiving evergreens in a US yard — it tolerates cold, clay soil, and low maintenance. But it has one genuine weakness: it cannot regenerate growth from bare wood. Unlike many deciduous shrubs that respond to hard cutting with vigorous new growth, arborvitae will not push new shoots from stems stripped of foliage. This single fact governs everything about how to trim it correctly.

Understanding arborvitae growth habit

Arborvitae grows from the tips of its branches outward and upward. New growth each season adds to the ends of existing branches. The interior of a mature arborvitae is brown — the foliage dies back naturally as interior branches are shaded out. This brown zone extends 6–18 inches from the trunk on a mature plant.

The green foliage zone — where all new growth occurs — sits on the outer 12–18 inches of the plant. This is the zone you can safely trim into. Any cut that removes all foliage from a stem produces a bare, permanently brown branch.

Emerald Green arborvitae — the most common privacy hedge variety sold at US garden centers — needs only one trim per year. Green Giant, which is often planted for fast screening, requires much more frequent attention.

When to trim arborvitae

The best time to trim arborvitae is late spring to early summer, after the new flush of growth has hardened. New spring growth appears light green and soft in May (earlier in southern US zones). By mid-June in most of the country, this growth has firmed up to a darker green.

Trimming at this point:

• Allows one full growing season for cuts to seal before winter
• Encourages the plant to fill in the trimmed areas before fall
• Reduces risk of fungal disease entering fresh cuts during summer humidity

Second trim option for fast-growing varieties: For Green Giant and Steeplechase, a second light trim in late July or early August helps maintain shape through the growing season without allowing too much regrowth.

What to avoid:

• Trimming in late fall or winter: fresh cuts entering cold weather do not seal well
• Trimming during drought stress: the plant is already stressed and does not heal easily
• Trimming in early spring before new growth hardens: this removes the season’s growth before it contributes to the plant’s density

Tools for trimming arborvitae

Using sharp, clean tools makes a measurable difference in outcome. Dull blades crush rather than cut stems, which browns cut edges and makes them more susceptible to disease.

Bypass pruning shears: For branches up to 1/2 inch in diameter and for detail trimming on individual branches. The bypass blade cuts cleanly on a scissors action. Do not use anvil-type pruners on arborvitae — the anvil side crushes the stem.

Hedge shears (manual or electric): For flat-surfacing a hedge line. Long blades make consistent flat cuts across dozens of branch tips at once. Electric models with 18–22 inch blades significantly reduce trimming time on long hedges.

Loppers: For branches thicker than 3/4 inch that shears cannot handle. Use bypass loppers, not anvil types.

Cleaning: Wipe blades with 70% isopropyl alcohol or a 10% bleach solution between plants. Arborvitae can develop fungal problems (Kabatina tip blight, for example) that spread on contaminated tools.

For more detail on pruning tool selection across different evergreen types, our arborvitae care guide covers variety-specific considerations alongside general culture.

How to trim arborvitae: step by step

Step 1: Assess the plant

Walk around the arborvitae and identify:

• Where the brown zone starts (how far from the outer surface)
• How much growth has occurred since the last trim
• Any dead, damaged, or pest-affected branches

Plan your trim to remove no more than one-third of the green growth. On a plant that has added 9 inches of growth, you can safely remove 3 inches.

Step 2: Start at the top

Trim the top first, then work down the sides. This prevents clippings from landing on areas you have already trimmed and requiring you to re-clear them.

For columnar arborvitae like Emerald Green, the top comes to a natural point. Resist the urge to flat-top a columnar variety — it destroys the natural form and creates a permanent wide spot.

For naturally pyramidal varieties like Green Giant, the top should be trimmed to maintain the natural taper, wider at the base and narrower at the apex.

Step 3: Shape the sides

Keep the base slightly wider than the top. This allows light to reach lower branches. A hedge that is wider at the top than the base causes lower branches to be shaded out and eventually bare.

For a privacy hedge, maintain the natural slight taper from base to top rather than trimming into a perfectly vertical wall. Vertical hedges shade their own lower sections.

Use a string line or chalk line for large hedges where you need a consistent flat surface. Stretch the string horizontally between two stakes at the height of your target trim line, then use the string as a visual guide.

Step 4: Remove interior debris

After trimming the outer surface, reach inside the plant and remove any dead brown twigs and accumulated debris. Dead material inside the plant can harbor fungal spores and should be cleared annually.

Step 5: Clean up

Collect clippings before rain. Wet clippings pressed against the plant can promote fungal disease. Compost clean clippings or dispose of them; do not compost if the plant has any disease or pest issues.

Trimming arborvitae that has gotten too large

The most common problem with arborvitae in US yards is that the plants grew much larger than the homeowner expected. Emerald Green is sold as a “small” variety, but at 10–15 feet it outgrows many foundation plantings. Green Giant reaches 50–60 feet if never trimmed.

If your arborvitae has grown past its target size, you have limited options:

Continue trimming to slow growth: annual trimming at the same height slows upward growth but does not stop it. The plant will continue adding a few inches per year even with annual trimming.

Lower the height gradually: you can reduce the height of an arborvitae over several seasons — 2–3 feet per year — as long as you do not cut below the green foliage zone. Dropping the height by 8–10 feet in a single session would expose brown wood and create bare patches.

Replace it: if the plant has grown to 25 feet and your target is 8 feet, replacement is the only practical option. Select a naturally dwarf variety for the replanting.

For guidance on choosing the right size arborvitae for a given space, our small evergreen shrubs guide and evergreen shrubs overview compare varieties with specific mature height ranges.

Trimming arborvitae hedges

A row of arborvitae planted as a privacy hedge requires slightly different technique than trimming individual specimens.

Before trimming: establish sight lines. Use stakes and string to mark your target height and width. Cutting a long hedge without guides produces waves and uneven sections that are hard to correct.

Trim in sections: work in 10–15 foot sections along the hedge rather than walking the entire length making small adjustments. Consistent passes produce more even results than many small cuts.

Maintain gaps between plants: arborvitae hedges are often planted 3–5 feet on center for fast screening. As the plants fill in, maintain small gaps between individual plant canopies. If branches of adjacent plants grow together and the connected area dies back from disease or weather, you will have a gap in the hedge with no green foliage on either side to fill it.

Dealing with brown patches

Brown interior patches are normal and unavoidable. They represent the plant’s natural self-shading of interior branches. You should not try to trim into or around them — that only exposes more brown wood.

Brown patches that expand to the outer surface of the plant are a different problem. Common causes:

• Winter burn: desiccation from cold dry wind. Prevention: anti-desiccant spray in late fall in zones 4–6, burlap windbreaks for exposed locations.
• Root problems: drought, waterlogged soil, or root rot cause dieback of whole branches. Check soil drainage and watering practices.
• Bagworms: caterpillars that build silk cases and feed on foliage. Common in central and eastern US. Remove bags by hand in winter and spray with Bt in early summer.
• Spider mites: more common in dry, hot summers. Look for fine webbing and yellowing foliage. Treat with insecticidal soap.

For other evergreen shrubs that require similar care, our Hicks yew guide, Blue Point juniper guide, and notes on how to prune lilacs cover the main alternatives for US privacy screens and foundation plantings.

The Penn State Extension publishes a guide to arborvitae diseases and problems that covers regional pest and disease identification for the northeastern US, where arborvitae is most commonly grown.

Trimming newly planted arborvitae

Newly planted arborvitae should not be trimmed for the first 1–2 years. Allow the plant to establish its root system before putting any stress on the canopy. An untrimmed first season also lets you observe the natural growth form and identify whether the variety will reach the size you expected.

Light shaping is acceptable in year two if the plant is growing vigorously. Do not trim to final target size in year two — give the plant at least one additional season to fill in naturally before imposing a tight shape.

Early training (gentle shaping from years 2–4) produces much better long-term results than hard correction of a large neglected plant in year 8.