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Western red cedar hedge trimming: timing, technique and the East Kent cutoff.

Thuja plicata is a faster-growing, better-smelling alternative to leylandii that handles the Wingham round well. It carries one rule that catches people out: cut it after August and you invite bare patches that nothing will fix come spring.

Western red cedar (Thuja plicata) is a conifer hedging species that has become genuinely common across the CT3 area over the past fifteen years, often planted where leylandii has fallen out of favour. It grows roughly as fast, handles exposed gardens on the A257 corridor without complaint, and smells pleasantly of apple and pine when the blade runs through it. The differences from leylandii that matter for maintenance: the August cutoff is stricter, the skin-irritation risk is real and often not mentioned, and on the chalk side toward Adisham and Bekesbourne, drought stress in a dry East Kent July changes the timing of the first cut in a way that leylandii does not demand to the same degree.

This guide covers the two-cut annual schedule, the August cutoff rule, and how the chalk-vs-Thanet-Sand split across the Wingham round changes what you do and when.

The two-cut schedule

A well-maintained thuja hedge needs two cuts a year to stay looking right: one in late May or early June, and the main annual cut in August. A hedge that is still establishing height can be managed with a single September cut while it reaches the target; once it is at the height you want, switch to two cuts to keep it dense and well-faced.

First cut: late May

The first cut tidies the spring flush before it makes the hedge look untidy through summer. In the CT3 area, late May is the usual target: the last frost risk is past by then on most plots, and the spring growth has put on enough length to be worth cutting without going over the same ground twice a fortnight later. There are two reasons not to go earlier. First, April frosts in the frost pockets along the Little Stour valley at Wickhambreaux come late enough in some years to catch freshly cut growth: the valley bottom sits lower than the road, and cold air settles into it overnight. Newly cut foliage on a thuja hedge in a Wickhambreaux garden has been caught by late April frosts that gardens 400 metres away on higher ground missed entirely. Wait for the settled late-May weather rather than cutting on the first warm April day. Second, the nesting window does not close until 31 August, so a nest check is required before the first cut. On plots where the thuja has been left uncut over winter and is particularly dense, a torch inspection inside the canopy is worthwhile.

Main cut: August

August is the most important cut of the year. It shapes the hedge going into winter, removes the summer's second flush of growth, and closes out the growing season before the plant goes into autumn slow-down. The nesting window closes on 31 August so any point in August gives you the cut before the window shuts; most jobs on this round are done in the second and third weeks of August when the first-cut growth has fully extended.

Aim to finish the August cut with two to three weeks to go before the end of the month so the freshly cut face has time to harden off before the nights shorten and cool. On the Thanet Sand ground east toward Ash, where thuja can grow strongly into late August in a warm year, watch that the last section of hedge is not cut so late that newly opened growth faces the first cool nights before it has any chance to settle. Mid-August is safer than 28 August on those plots.

The August cutoff: why late-season cutting causes bare patches

This is the rule that catches thuja owners out most often. Unlike yew, which can be cut into mature wood and regenerate reliably, thuja plicata will not recover well from any growth cut after August. The mechanism is straightforward: growth cut in September or October puts out a small amount of new foliage before the plant effectively stops for winter. That new growth has not had time to harden, and the first frosts kill it. Where it dies, the foliage drops, and what is left is the brown inner wood that will not regenerate to green. Come spring, those sections stay brown. On a thuja hedge that has been cut late for two or three seasons, the brown patches become permanent features of the face.

The only fix is time, and even then recovery is partial: the neighbouring green growth gradually encroaches over the brown sections over two or three growing seasons, but it never quite covers fully in the way a well-maintained hedge would look. Prevention is the only real answer. If you have missed the August window, leave the hedge untouched until the following May rather than cutting in autumn.

How chalk and Thanet Sand change the schedule

Chalk-side gardens: Adisham, Bekesbourne and higher ground north of the A257

On the shallow chalk that runs south-west of Wingham toward Adisham and Bekesbourne and on the higher, drier ground around Ickham and the approaches to Preston, thuja is more vulnerable to summer drought than it is on the moister soils further east. The East Kent dry-belt effect is pronounced on chalk: the soil holds very little water, and from late June through August in a normal year the upper horizon can be genuinely parched. A thuja hedge under this kind of moisture stress will already be showing some browning at the shoot tips before August arrives. Cutting into that stressed foliage concentrates the visible damage at the cut face and risks triggering a worse browning response than if the hedge had been left.

The practical rule for chalk-side gardens: check the shoot tips before the August cut. If the tips are already browning or dull rather than bright green, water the hedge thoroughly at the base, wait a week for the plant to recover some turgor, and then cut. Cutting a drought-stressed thuja is one of the main ways a hedge that looked recoverable in July looks genuinely tatty by September. A mulch layer 7 to 10 centimetres deep at the base of a thuja on shallow chalk makes a real difference to how the plant carries through the dry East Kent summer and how it looks when August trimming is due.

Thanet Sand toward Ash, Staple and east of Wingham

East of Wingham along the A257, the ground shifts to Thanet Sand: freer-draining but warmer in spring, with a growing season that starts earlier than on the chalk. Thuja on Thanet Sand pushes its spring flush out noticeably faster than the same plant on chalk, which means the first cut target moves earlier. In a mild spring, late April is sometimes the right window for the first cut on sandy ground around Ash and Staple, a full three to four weeks before the chalk-side gardens need the same job done. The summer growth is also more vigorous, and thuja on Thanet Sand often puts on enough of a second flush by mid-summer to warrant the August cut at the earlier end of the window, around the 10th to 15th, to leave time for the cut face to settle before growth slows.

The one advantage of Thanet Sand over chalk for thuja is moisture: the soil drains fast but it does not hold the plant under the same level of drought stress that shallow chalk imposes. In a dry July, sandy-ground thuja hedges near Ash typically look healthier than chalk-side hedges toward Adisham, and the cut tends to produce a cleaner result because the foliage is not already stressed before the blade moves.

Growth rate and the A-profile

Thuja plicata is a fast-growing species: a well-established hedge in a CT3 garden will typically extend 30 to 50 centimetres in a season, roughly comparable to leylandii but slightly less aggressive in most soil conditions. The same A-profile discipline that applies to any conifer hedge applies here: keep the hedge wider at the base than the top by 5 to 10 centimetres per metre of height. A thuja hedge cut with flat vertical faces or, worse, an inverted profile will shade its own lower section and lose density at the base within a few seasons. The hedge trimming technique guide covers the A-profile and string-guide method in detail; the same approach works for thuja as for leylandii and any other formal conifer hedge.

One thuja-specific note on profile cuts: because the foliage is feathery and the growth-tip density is high, thuja hedges are often cut slightly too tight when owners are aiming for a neat result. Leave a little headroom inside the profile at the May cut, particularly on the Thanet Sand ground where growth extends strongly through summer: allow the August cut to bring the hedge back to the target rather than trying to arrive at the finished outline in May and then finding it has grown past it by July.

What to do with an overgrown thuja

A thuja hedge that has been left without cutting for several years presents the same constraint as leylandii: you cannot cut back hard to old brown wood and expect recovery. The approach is staged reduction over two or three winters. In the first winter (October through February, outside the nesting window), reduce the top by a third. In the second winter, reduce by another third. By the third growing season the hedge can be managed at the target height and density. Reduce the sides separately from the top, and reduce each face in stages rather than trying to do both sides and the top in the same season: the hedge needs enough green surface to continue photosynthesising through the reduction process.

The staged leylandii reduction guide on this site uses leylandii as its worked example, but the three-winter principle and the constraints on cutting to bare wood apply to thuja in the same way. The one difference is that thuja is slightly more forgiving about cuts that nick into older wood by a few centimetres than leylandii is, but that tolerance is limited and should not be relied on as a justification for cutting aggressively.

Conservation area and Section 211

If a thuja hedge sits within the Wingham Conservation Area and any structural stem measures over 75mm diameter at 1.5 metres, a Section 211 notice to Dover District Council is required before any work on that stem, with a six-week wait before cutting. Annual trimming of a well-maintained thuja hedge will not normally bring stems into the Section 211 range, but a hedge left without cutting for several years can accumulate structural stems that do. Measure the base stems before any work involving loppers or a saw. The Section 211 guide on this site covers the filing process and what counts.

Video credit: Ken Crowther, “Hedge to perfection: Thuja cutting” series, YouTube. Ken Crowther is a UK-based gardening broadcaster with a regular slot on BBC Essex and has presented hedge and garden care content for over a decade. The three-part thuja series (2023) covers tool selection, technique and timing for the UK climate.

Common questions

When should I cut my thuja hedge in Wingham?

Twice a year for a well-maintained hedge: the first cut in late May (after the last frost risk in CT3 and once the nesting-season check is done), and the main cut in August before growth slows in autumn. Do not cut after August: late autumn cuts leave new growth exposed to dieback before it has time to harden off, and any bare patches that develop will not fill from old brown wood.

Can I cut a thuja hedge back to old brown wood?

No, not reliably. Unlike yew, thuja plicata will not regenerate from old brown wood at the centre of the hedge. Always keep the cut into the green outer layer of growth. This is the same rule as leylandii and the reason staged reduction over two or three seasons is the right approach for an overgrown western red cedar, not a single hard cutback.

Why does my thuja hedge go brown and patchy after trimming?

The two most common causes in CT3 are cutting after August (new growth cannot harden before winter) and cutting into old brown wood beyond the green outer layer. A third cause specific to the chalk-side gardens near Adisham and Bekesbourne is drought stress: trimming a thuja that has already browned at the tips from summer moisture stress concentrates that visible damage at the cut face. Water thoroughly and wait for the plant to recover before cutting in a dry year.

Does cutting thuja cause skin irritation?

It can. Some people react to thuja plicata sap and the aromatic oils released when the foliage is cut. Wear long sleeves in addition to gloves and eye protection when trimming. The reaction is a contact dermatitis rather than an allergic response in most cases, but repeated exposure can sensitise people who were not initially affected. The scent when cutting is pleasant, apple-like, but that should not lead you to treat the sap as harmless.

Sources: Wildlife and Countryside Act 1981 s.1; RHS, Pruning Hedges: Expert Tips; RHS plant profile, Thuja plicata (AGM); Ashridge Trees, Western Red Cedar hedge care notes; BBC Gardeners' World Magazine, “How to Grow Western Red Cedar (Thuja plicata)”; Cranfield Soilscapes chalk and Thanet Sand soil series notes; Met Office South East England regional climate summaries.