← All guides · Hedge trimming technique · Updated October 2026

How to trim a thuja (western red cedar) hedge in Canterbury. Timing, the old-wood rule and renovation.

Thuja plicata is a sensible answer to enquiries that start with "we want something like a leylandii, but without the problems." It gives you the same evergreen density and reasonably fast growth, takes a regular clip without complaint, and is generally regarded as more forgiving than leylandii if a hedge is let go. But it is still a conifer: do not rely on it regrowing from bare brown wood. For a conifer hedge in CT1 to CT4, that distinction matters.

The August main cut

The standard thuja maintenance cut falls in August. The reason is giving the plant enough time for any new growth stimulated by the cut to harden before the first frosts. Cut in September and a late flush stays soft through October; a cold night browning soft conifer tips is a cosmetic problem that takes a full growing season to grow through.

In practice, August gives several weeks of hardening time before the first autumn frosts, which typically arrive from mid-October onwards. That margin is comfortable on most plots. A cut in the last week of August works well. A cut in mid-September is pushing it on an exposed position.

For a thuja managed at a consistent established height, one or two cuts a year is usually enough: a light spring tidy and the August cut. If the hedge is well established and you are purely maintaining shape, August alone is often sufficient.

The optional April spring tidy

If a thuja has put on substantial extension growth between September and April, a light tidy in April takes that back without disrupting the main late-summer growth cycle. Keep it genuinely light: run the blade back to the established line on the sides and remove any top growth that has visibly overshot. Do not take the top down in April if you are also planning an August cut. Taking the same growth twice over the same season puts the plant under unnecessary stress and encourages the kind of patchy recovery that makes the hedge look uneven through the following year.

April is inside the nesting season, so the same rule applies as for any other cut: the 1 March to 31 August window is accepted guidance rather than statute, and nesting can begin before or continue after it. Great tits and blue tits can be in nest boxes and cavities in late March, and a blackbird nest at the base of a dense thuja hedge can appear from early April in a mild spring. A visual check before you put the blade to the hedge is always the right starting point, whatever the calendar says.

Nesting season and the law

Under the Wildlife and Countryside Act 1981, section 1, it is an offence to intentionally damage or destroy a wild bird's nest while it is in use or being built. The penalty can be a fine (unlimited in England and Wales) and up to six months in prison. The Act sets no calendar dates; 1 March to 31 August is the accepted guidance for the main nesting season.

For thuja specifically, the dense spray-like foliage makes a useful and popular nesting site: dunnock, wren and robin all use the interior of a well-established thuja hedge. The density that makes thuja such an effective screen also makes it hard to see a nest without actively looking. The check takes two minutes. Stand at the hedge face, look at chest height, listen for alarm calls, and part the outer foliage with a gloved hand at intervals along the run before the blade starts. If you find an active nest with eggs or chicks, stop, put the equipment away, and come back once the birds have finished with it.

Old wood and renovation: be cautious

This is where thuja and its relatives need care. Most conifers, leylandii most famously but also many cypress relatives, do not regenerate from cuts into the bare interior wood. The green zone on the outer face is all the living tissue the plant carries on any given face. Cut past it and that face may stay bare. It is a one-way boundary.

Opinions differ on how much thuja plicata forgives. Some growers report it pushing new green shoots from old brown wood over a season or more; others find it slow and unreliable, and the safe advice is not to count on it. Yew is the conifer that genuinely welcomes a hard cut; thuja is not in the same league. If you do need to cut a thuja hedge back harder, cut to where you want the permanent face to be, leave it a full season without further trimming, see whether it re-clothes that surface, and only then resume normal maintenance cuts. For a general video demonstration of cutting a thuja hedge, see this thuja hedge cutting video.

The practical implication is that a thuja hedge allowed to grow out over several years is best brought back in stages, staying inside the green foliage, rather than in one drastic cut. For leylandii hedges that have grown too tall, our staged leylandii reduction guide covers the two-year sequence that works within a conifer's limited ability to regrow.

Blade choice and trimming technique

A powered hedge trimmer handles almost all thuja maintenance work cleanly. Thuja foliage is soft and spray-like, composed of flat overlapping scale-leaves rather than the large, easily bruised leaves of cherry laurel or Portugal laurel, and it does not have the hard-needled resistance of holly. A standard double-sided blade works well across both faces of the hedge in a single pass. For the top on a tall run, anything above shoulder height, a pole attachment or a dedicated pole hedge trimmer keeps the cut level and reduces time on a ladder or platform.

The most common technique error on thuja hedges is cutting too deeply into the sides on a maintenance pass. The green zone is shallower than people think on a well-maintained plant. Before the first cut of the season, push a gloved hand into the canopy horizontally to feel where the foliage thins and the bare stems begin. That depth is your limit for a maintenance cut. Go further and you are in renovation territory, which should be a planned decision, not an accident.

Thuja produces a distinctive aromatic scent when cut, the source of the "western red cedar" association though thuja is technically a cypress relative rather than a true cedar. Most people find the scent pleasant at moderate exposure. Prolonged cutting of a long run can be eye-irritating, and some people with resin sensitivities find the sap causes a skin reaction through thin work gloves. Safety glasses and close-fitting gloves are the minimum. For the full pre-cut protocol covering RCD adaptors, footing checks and blade maintenance, see our hedge trimmer safety guide.

Thuja on chalk: establishment and first-year feeding

Thuja plicata grows happily across a wide soil range, but it wants more from the ground than very thin chalk topsoil. Shallow, fast-draining chalk does not hold the nitrogen the plant needs to put on confident early growth. Apply a slow-release balanced granular fertiliser in late March, worked lightly into the surface over the root zone. One application per year, for the first three seasons, is usually enough. After that, an established thuja manages well on whatever organic matter accumulates in a maintained mulch layer, though it will need watering in prolonged dry spells.

On the deeper Stour valley loam, thuja establishes faster with no supplementary feeding needed. The risk on those plots is waterlogging through a wet winter. Thuja tolerates brief wet spells but dislikes prolonged root saturation. If the planting site sits in a frost pocket or stays wet from November through to March, a shallow raised bed or a drainage spit into the subsoil will extend the hedge's long-term health considerably. For a fuller breakdown of which species suit which local soil, see our guide to hedge species for Canterbury chalk and valley loam.

Disposing of thuja clippings

Thuja clippings can go in the Canterbury City Council garden waste (green wheelie) bin, subject to the service's normal mid-December to mid-January break; the 2026/27 subscription is £65 for the first bin and £56.48 for each additional. If the annual clip of a long run produces more volume than the bin allows, the Vauxhall Road Household Waste Recycling Centre accepts garden waste Monday to Saturday, 08:00 to 16:30 (Sunday 09:00 to 16:00), free for Kent council-tax payers; note the 2m height barrier at the entrance. Thuja clippings can also go into a domestic compost heap. They break down more slowly than soft green material but will not impede a working heap.

Sources: Wildlife and Countryside Act 1981, section 1; Royal Horticultural Society Thuja plicata plant profile and hedge pruning guidance (rhs.org.uk); RSPB and GOV.UK nesting-season guidance; Canterbury City Council garden waste subscription 2026/27; Kent County Council household waste recycling centres.