← All guides · Cutting technique · Updated September 2026

How to prune a Western Red Cedar hedge in Broadstairs: timing, the green-zone rule and CT10 coastal notes for Thuja plicata.

Thuja plicata is the sensible alternative to Leylandii for CT10 gardens: faster to establish than yew and more aromatic than Leylandii, and it copes reasonably well with coastal wind. The pruning rule is the same as for any conifer except yew: leave green on every cut face, always. Cut into brown and it stays brown. This guide sets out the two-cut year, the timing that works for Broadstairs, and the renovation question that comes up on older hedges that have been left to run.

Steps

Step 1: Check for nesting birds before picking up any tool

Walk the entire length of the hedge before you do anything else. Work slowly along each face, watching for adult birds flying repeatedly into the same section, for alarm calls, and for any sign of a nest interior through gaps in the foliage. Thuja plicata 'Atrovirens' grows dense enough to conceal blackbird and song thrush nests easily, and the aromatic foliage makes a probe from the outside unreliable. If you find a nest with eggs or young, or a bird behaviour pattern suggesting an active nest you cannot see, stop and reschedule.

Step 2: Identify the green zone on each face before starting

Stand back from the hedge and look at each face in turn. The green zone is the outer layer of living foliage: the depth of growth that is actively photosynthesising and can regenerate after a cut. Behind it lies the brown interior zone: bare old wood and dead branchlets that carry no green growth and will not produce new shoots after cutting. The width of the green zone varies by how recently the hedge was last trimmed and by growing conditions.

On a regularly maintained thuja hedge in CT10 conditions (moderately fast growth, two cuts a year), the green zone on each side face typically runs 8-15 cm deep in late spring at first-cut time. On a hedge that has been left for two or three years, the green zone may still be 15-25 cm on the favoured (south or southwest) face but shallower on the north-facing or salt-exposed face. Your cut must not go deeper than the inner edge of the green zone on any face. Mark that depth in your mind before lifting the trimmer.

Step 3: First cut in May, working sides then top

The first cut of the year should happen in May, once the winter's new growth has hardened slightly but before the summer growth flush runs away. In CT10 conditions, late April is often still too cold at night for fresh cuts to heal cleanly; early June risks leaving too much growth to remove in one cut without hitting old wood. I aim for the second half of May on most Broadstairs gardens.

Work the sides before the top. Start at one end of the hedge and trim from the base upward, applying the batter angle throughout: the cut face should lean inward as you move up, so the top of the hedge is narrower than the base. On a 2m thuja hedge, a batter of 10-15 cm narrower on each side at the top than at the base is about right. The aromatic lemon-cedar scent that comes off fresh-cut thuja is a useful reassurance that you are cutting live green foliage; if the scent disappears on a section mid-run it often means you have moved into the brown zone and should check the cut depth before going further.

For the top, use a string guide line between two canes set at the finished height. Work along the top with the trimmer held horizontally and the blade just below the line. Step back every 3-4m to check the level by eye: the string line is a reference, not a guarantee on a hedge with uneven previous growth.

Amount to remove at the first cut: aim to take back to just within the previous cut line, removing the winter's new growth plus a centimetre or two. On a thuja growing 30-40 cm per year in Broadstairs conditions, that means removing 15-25 cm of new growth at the first cut, leaving a green face throughout.

Step 4: Allow 8-10 weeks for new growth to return to green, then time the second cut

After the first cut, the freshly exposed cut surface browns slightly as the cut foliage dries. Within 4-6 weeks in a CT10 summer, new green growth breaks from the cut points and by 8-10 weeks (typically late July to early August) the outer face has returned to green. Do not make the second cut until this has happened on all faces. Cutting into the still-browning surface from the first cut does the plant no harm biologically, but it extends the period the hedge looks unsightly and reduces the density of the new growth layer.

The second cut should land in late August for most Broadstairs gardens. This timing satisfies three constraints at once: the nesting season is effectively over (or nearly so); the new growth has had time to become a solid green layer; and the cut heals and re-greens before the first autumn frost, which on the Thanet coast typically arrives in late October. Cutting in September is not disastrous but leaves less recovery time before cooler nights slow regrowth.

Step 5: Make the second cut lighter than the first

The second cut is a tidy and shaping pass, not a structural reduction. Remove the summer's growth back to just beyond the May cut line: typically 10-20 cm on a thuja growing at CT10 rates. The sides should be worked first, then the top. Apply the batter angle again on the side faces: it is easy to let the batter drift toward vertical over successive cuts, so check from the far side of the garden before finishing.

Avoid cutting in bright midday sun on a warm day. Freshly cut thuja foliage is sensitive to solar scorch in the first 24-48 hours after the cut: the cut surface loses moisture faster than the plant can replace it and the tips brown. On exposed CT10 sites above the clifftops at Kingsgate, North Foreland or Stone Bay, where the combination of salt air and direct sun is most intense, I schedule the second cut for morning work on a dry day with a light breeze rather than a still, sunny afternoon.

Step 6: Clear clippings, check the profile, and note the finished dimensions

Lay a tarpaulin before starting (or fold it in after the cut) and carry the clippings to a compost heap or green waste bag. The RHS notes that some gardeners have reported skin irritation after handling Thuja plicata trimmings, so wear long sleeves in addition to gloves and goggles. Do not leave them on the lawn: the aromatic oils slow decomposition and the clippings mat into wet coastal-climate lawns quickly.

Stand back and read the finished profile from 6-8m. The sides should read as a gentle A-shape, the top as a level line. Note the height and the width at the base and top: keeping a simple record means you can repeat the same cut dimensions next year and catch any drift toward a vertical-sided profile before it becomes a problem at the base. On a Broadstairs garden with limited winter light, a gradually widening basal width and a narrowing top is the most common slow failure in thuja hedges maintained without a string line.

Thuja or Leylandii? The CT10 case for Western Red Cedar

Both are large, fast-growing evergreen conifers used primarily for screening and privacy in UK gardens. Leylandii has been the dominant choice since the 1960s but its reputation is largely earned through the consequences of under-maintenance rather than any intrinsic fault of the plant. Thuja plicata 'Atrovirens', the form planted in most UK hedging schemes, has several practical advantages for Broadstairs situations.

First, the foliage. Thuja carries flat, fern-like sprays of rich, dark green foliage with a pronounced lemon-cedar scent: a markedly more attractive surface than Leylandii's grey-green, and more tolerant of partial shade on east-facing plots. Second, the wildlife value. Both give dense cover for small nesting birds, so the nest check applies equally to either. Third, the salt-wind performance. Thuja plicata copes reasonably well with coastal wind, from sheltered road frontages through to moderately exposed positions on the clifftop terraces above Stone Bay and Kingsgate.

The limit for thuja on the Broadstairs coast is the most exposed clifftop positions, particularly those on the northeast-facing chalk escarpments above Joss Bay and North Foreland. Here the direct North Sea gale track in autumn and winter causes more foliage damage to thuja than to the salt-hardened Escallonia or Griselinia that perform best in those exposed positions. For a sheltered front garden, including in the conservation areas, thuja is an excellent choice.

The scent as a working indicator

The lemon-cedar scent of Thuja plicata is more than a pleasant characteristic: it can be a rough working signal. Strong, clean scent as you cut means you are in live green foliage. A diminished or absent scent mid-run, when cutting at the same angle and depth as a section that did smell, often means you have drifted into the brown dead-wood zone. The dead interior wood of an established thuja carries essentially no scent, having none of the aromatic resins of the live outer growth. If you notice the scent disappear, pull back the trimmer and check the cut face before going further.

The scent also fades naturally through the cutting day on already-cut sections: this is normal and not a sign of cutting into dead wood. The live-vs-dead indicator works best when you are actively cutting a new section, not when you are standing beside a section cut 20 minutes earlier.

The renovation question: what Thuja can recover from

Like Leylandii and most other conifers (yew is the exception), Thuja plicata does not reshoot from bare old wood, as the RHS says of conifer hedges generally. Thuja will only produce new growth from wood that still carries a little green: if there are small green shoots or a thin fringe of live foliage visible on an older branch, cutting back to just above those shoots can produce recovery.

The limit is bare brown wood with no green growth from it at all. No amount of encouraging conditions will produce new shoots from completely dead interior wood on thuja. A hedge that has been allowed to grow outward to the point where the outer green zone is more than 25-30 cm thick on each face, and the total width is substantially greater than the required finished width, cannot be cut back to size in a single year without exposing brown dead wood. The standard approach for an overgrown thuja hedge in CT10: staged reduction over two seasons. In year one, take the sides back by approximately half the excess, leaving a green surface throughout. Allow the plant a full growing season to push new growth from the cut faces. In year two, cut back further to the desired finished dimension. This approach works on most overgrown thuja hedges if the brown-wood exposure in year one is minimal.

For hedges that have been completely neglected for five years or more and are now three or four times their desired width, honest assessment before renovation is worthwhile. Where the brown zone is too wide on all faces, staged reduction produces an unattractive result, and replacement with young pot-grown stock is the faster route to a well-shaped hedge.

Chalk soil and Thanet conditions

Thuja plicata is less particular about soil than its conifer relatives Lawson cypress or most pines. It tolerates the shallow alkaline Margate Chalk formation under CT10 better than most conifers, provided the planting hole is improved with organic matter at establishment. The key risk on chalk is drought: thuja established on thin chalk soils above the free-draining Upper Chalk can suffer foliage browning in a hot, dry summer. In the establishment years (the first three after planting), a drip hose or hand-watering during dry spells in May to August is worth the effort. Established plants with a root system that has reached deeper chalk layers and any clay-with-flints sub-horizon are markedly more drought-tolerant.

Thanet gets around 615mm of rain a year, which is on the dry side for thuja. Where the chalk is very shallow, as it can be on some clifftop plots, a more drought-tolerant species such as Escallonia or Griselinia may establish more reliably.

Sources: Ken Crowther / World Radio Gardening (worldradiogardening.com), "August jobs for the garden and cutting back a thuja hedge" (YouTube, 29 July 2023; youtube.com/watch?v=TbMuepNchlc); Ken Crowther / World Radio Gardening, "Hedge to perfection 2/3: Thuja cutting with Ken Crowther" (YouTube; youtube.com/watch?v=woyBuvSaEik); Ken Crowther / World Radio Gardening, "Hedge to perfection 3/3: Thuja cutting with Ken Crowther" (YouTube; youtube.com/watch?v=Eb8cehcQHeE); BBC Gardeners World Magazine, "How to Grow Western Red Cedar (Thuja plicata)" (gardenersworld.com, January 2024); Ashridge Trees, Western Red Cedar hedge plants product guide (ashridgetrees.co.uk); Hopes Grove Nurseries, Thuja hedging expert advice (hopesgrovenurseries.co.uk); Hedging Plants Direct, Thuja hedge care guide (hedgingplantsdirect.co.uk, August 2026); Hedges Online, Western Red Cedar Hedging (hedgesonline.co.uk); Best4Hedging, Western Red Cedar hedge plants (best4hedging.co.uk); British Geological Survey, Upper Chalk Bedrock, SE England; Royal Horticultural Society, "Pruning hedges" (rhs.org.uk/plants/types/hedges/pruning-hedges); Met Office, Manston climate averages 1991-2020; Wildlife and Countryside Act 1981, s.1.