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Thuja plicata (western red cedar) hedging on the Dover coast: exposure grade, chalk soil and trimming timing.

Western red cedar is the hedging industry's most-promoted alternative to Leylandii. It is fast-growing, evergreen, holds a dense face well, tolerates chalk soils, and, unlike Leylandii, can regenerate from older wood, which makes renovation possible when the hedge has been left to run on. The coastal question matters more than most garden-centre advice acknowledges. The 'Atrovirens' cultivar, which is virtually all that is available for hedging in the UK, is noted by leading UK nurseries as intolerant of coastal areas. At the most exposed clifftop and Bay positions above St Margaret's Bay, Thuja plicata shares Leylandii's core weakness: cold desiccating easterlies and salt-laden westerlies damage young plants and slow establishment significantly. In village and sheltered positions it is a genuinely good choice. Understanding that split is what this guide is for.

What Thuja plicata is

Thuja plicata is a large conifer native to the Pacific coast of North America, from northern California up to British Columbia and south-east Alaska, where it reaches heights of 50 to 65 metres as a free-standing forest tree. In the UK it is grown almost exclusively as a clipped hedge or tall screen, kept by regular trimming to practical heights between 1.5 and 5 metres. The common name western red cedar refers to the reddish-brown timber of mature trees, not to any relationship with true cedars (which are Cedrus species). Older nursery catalogues may list it as Thuja gigantea or Thuja lobbii, both former synonyms. The cultivar used for hedging is almost universally 'Atrovirens', which has dense dark-green foliage and a tighter, more upright habit than the species when free-growing. It is also sometimes sold as 'Western Red Cedar' without a cultivar name, in which case 'Atrovirens' is almost certainly what you are getting.

The foliage is flat, scale-like and aromatic: when clipped, the cut foliage releases a distinctive fresh scent, sometimes described as pineapple or sweet apple, that is quite different from the faintly unpleasant smell of cut Leylandii. This is the sensory detail that makes Thuja a noticeably more pleasant hedge to work with. The flat fronds are dark glossy green on the upper surface and paler below.

The key advantage over Leylandii: it can regenerate from older wood

The most important practical difference between Thuja plicata and Leylandii (x Cuprocyparis leylandii) is that Thuja can regenerate from older wood that has lost its green cover, within limits. Leylandii will not produce new growth from bare brown wood under any circumstances: cut past the green outer layer and that face stays bare permanently. Thuja is more forgiving. Provided there are living cells present in the brown older wood, and provided the cut is not made excessively deep into the main trunk, new growth will emerge over the following two to three seasons. This is why staged renovation of an overgrown Thuja hedge is genuinely practical in a way that staged leylandii reduction is not: you can take the hedge harder in each stage because the recovery potential is real.

The limits matter. Hard renovation, cutting well into old wood, should still be done in stages rather than in a single pass, and the regeneration is slower in the first year than an established hedge's normal response to an annual trim. On exposed inland sites, and particularly in the sheltered positions in the CT16 and CT17 area where the growing season is good, a hard-renovated Thuja hedge will have mostly greened back across the cut face within two years. At village positions in St Margaret's at Cliffe and Kingsdown, three years should be allowed. For the full staged renovation approach to conifers, see our guide on staged leylandii reduction, noting that the staging intervals can be shorter for Thuja because of this recovery advantage.

Growth rate, hedge height and how often it needs trimming

Thuja plicata 'Atrovirens' grows fast: 30 to 40 centimetres per year in reasonable conditions is a reliable expectation, and in a good sheltered position with adequate moisture at the roots it can exceed that. This is broadly comparable to the growth rate of Leylandii in its early years, and it is faster than nearly all the broadleaf evergreen hedging plants we cover for this coast. The fast growth is an advantage if you want a screen quickly, and a management commitment if you want to keep the hedge at a fixed height. A hedge left without trimming for two seasons becomes noticeably harder to bring back to a clean formal face, because the new growth firms up and the hedge widens at a rate that makes each season's postponement compound the problem.

An established Thuja hedge at a working height of 2 to 3 metres will typically need trimming twice per year to stay looking tidy: once in late winter or early spring, and once in late summer to early autumn after the growing season's main flush. A single trim per year, in early September, is acceptable if you are tolerating a slightly less formal finish, but the second trim makes a meaningful difference to the quality of the face. Gardeners' World notes that faster-growing conifers can need up to three cuts per year for a tightly formal finish, though in practice most domestic boundaries are maintained well on two.

Planting in chalk soil at St Margaret's

Container-grown stock is the right choice for Thuja on the chalk soils between Ringwould and South Foreland. Ashridge Trees confirms Thuja tolerates chalk and any fairly well-drained soil, which applies directly to the free-draining chalk-based ground common in the CT14 to CT15 area. The same chalk planting principles that apply to other hedging species here apply to Thuja: work in organic matter at planting to give the root ball a moisture buffer against dry spells in the first summer, and water during any dry period in the first growing season. For a full account of the techniques that work on this specific soil type, see our chalk-soil hedge establishment guide.

For a single-row formal boundary hedge, plant at 60 to 75 centimetres apart, which matches the advice from Gardeners' World and hedging.co.uk. This spacing gives a hedge that closes up within two to three growing seasons and leaves enough room for each plant to establish without competing too tightly for moisture in the chalk soil during the first summer. Some suppliers recommend 3 plants per metre (roughly 33 centimetres), which creates a faster initial screen but puts more pressure on root moisture in a free-draining soil and does not produce a noticeably better long-term hedge. On the chalk soils of this coast, the wider spacing is the more sensible call.

For village and sheltered positions, both autumn and spring planting work. Autumn planting from October to December lets the roots establish through the mild part of the year before the growing season begins in spring, and is the approach that captures the most growth in the first year. At inland-facing gardens in St Margaret's at Cliffe, Kingsdown and Walmer that are away from direct cliff exposure, there is no strong reason to prefer one season over the other: both work. If you are on a boundary where winter wind tunnels between buildings, spring planting reduces the risk of the new plants sitting in heavy cold winds before they have anchored properly.

Trimming timing: the nesting-season window on the Dover coast

The practical trimming calendar for a Thuja hedge on the Dover coast needs to fit around two constraints: the bird nesting season, and the growth calendar that determines when each cut does the most good.

The Wildlife and Countryside Act 1981, section 1, makes it a criminal offence to damage or destroy an active wild bird's nest or to disturb a bird on or near such a nest. For practical purposes, the nesting season runs from 1 March to 31 August. Thuja hedges, with their dense evergreen foliage, are used as nesting sites by a range of species including dunnocks, robins and wrens, and a visual check for active nests immediately before any trim in this window is required. For a full breakdown of how the nesting-season law applies along the coastal cutting calendar, see our hedge cutting timing and nesting season guide.

The trimming windows that fit best around the nesting season on this coast are late February and September. Late February, specifically the last week of the month, catches the hedge before the 1 March nesting-season start while the growing season has not yet fully begun. A clean trim at this point shapes the hedge before the main spring growth flush and does not leave the cut ends exposed to prolonged hard frost in the way that a December or January cut can, since the severest frosts on the Dover coast typically fall in January and early February rather than late in the month. September is the main autumn trimming window across the site, after the 31 August nesting-season closure and before the weather closes in. A September trim that catches the late-summer growth keeps the hedge tidy over winter and reduces the weight of foliage that carries Channel gale loading in autumn and winter storms.

For the spring trim in late February, the visual nesting check is still required: some birds, particularly wood pigeons, begin nesting activity before 1 March in mild years, and a check takes two minutes and avoids any legal exposure. If an active nest is found, that section should be left untrimmed until the nest is confirmed empty, then tidied in September.

Avoid trimming in October and November. A late-autumn cut on Thuja stimulates soft new growth that has no time to harden before the first significant frosts. On the Dover coast, where cold Continental air can push temperatures well below zero by early November, that soft new growth is vulnerable to frost scorch. The damage is cosmetic rather than fatal, but it leaves the hedge looking brown-tipped through the winter and is easily avoided by keeping the autumn cut to September.

Thuja versus Leylandii: where the comparison holds and where it breaks down

The standard market claim for Thuja plicata 'Atrovirens' as a Leylandii alternative centres on three points: similar growth rate, dense evergreen screen, and the renovation advantage. On those three counts the comparison is fair. Where it breaks down, particularly on the Dover coast, is in coastal tolerance. Leylandii performs poorly on direct clifftop positions: salt wind and cold desiccating east winds damage it during establishment and it never achieves the same density it would in a sheltered position. Thuja plicata 'Atrovirens' has the same limitation, noted explicitly by UK nurseries in a way that Leylandii usually is not. If someone is looking for an alternative to an existing clifftop Leylandii hedge that has failed, Thuja is not the right answer for that position. The right choices for clifftop windbreak and screen hedging on this coast are covered in our salt-wind resilient species guide.

Where the comparison holds cleanly is in the village gardens of St Margaret's at Cliffe, the back-street gardens of Kingsdown, and the sheltered plots of the Walmer and Deal corridors. In those positions, an owner who wants the fastest possible dense evergreen screen, and wants the option of hard renovation if the hedge is ever left to run on, will find Thuja plicata 'Atrovirens' delivers on its marketing. The aromatic cut foliage is a genuine bonus for anyone who has to maintain the hedge themselves: the smell when clipping is noticeably pleasanter than working with Leylandii.

One point worth noting for gardens where wildlife value matters: Thuja provides good nesting cover and the dense foliage gives winter shelter for small birds, but it provides no berries or nectar. A mixed native hedge, or a hedge that includes a berry-bearing species alongside the Thuja, will serve wildlife significantly better than a single-species Thuja boundary.

Existing Thuja hedges at clifftop positions

Not all the guidance above applies to an established Thuja hedge that has been in place for many years at a clifftop position. A mature Thuja hedge that has built up a dense root system and has adapted over years to its specific exposure can continue to perform even at positions that would be difficult for a newly planted young plant. In those cases, the right approach is to maintain the existing hedge rather than remove it. Trimming twice per year, keeping the hedge at a manageable height, and watching for signs of wind damage or browning on the seaward face are the practical tasks. If a significant section of an established clifftop Thuja hedge has died back following a severe storm or an unusually cold winter, the question of whether to patch it or remove and replant with a more suitable species is worth thinking through carefully on a site-by-site basis before deciding.

Sources: Royal Horticultural Society, Thuja plicata plant entry (rhs.org.uk/plants/18154, noting chalk, clay, loam and sand soil suitability and the need for shelter from cold drying winds); Ashridge Trees, Western Red Cedar hedging page (ashridgetrees.co.uk, confirming chalk and any well-drained soil tolerance and trimming guidance); Gardeners' World, Western red cedar (gardenersworld.com, advising 60 to 75cm planting spacing and twice-to-three-times-per-year trimming for fast conifers); hedging.co.uk, Thuja plicata Atrovirens page (hedging.co.uk/thuja-plicata-atrovirens, confirming 60cm spacing); Majestic Trees, Thuja plicata Atrovirens hedging listing (majestictrees.co.uk, noting intolerance of coastal areas for the Atrovirens cultivar); Wildlife and Countryside Act 1981, section 1 (nesting season, offence to damage or destroy an active nest, 1 March to 31 August). Place names verified: St Margaret's at Cliffe (CT15, OS grid TR374448), St Margaret's Bay (CT15), South Foreland (CT15), Kingsdown (CT14), Ringwould (CT14), Walmer (CT14), Deal (CT14), Dover (CT16/CT17).