Western red cedar hedge: the trimming questions we get in Rochester.
A lot of the privacy screening planted around Cuxton, Frindsbury and the Halling road estates in the 1980s and 1990s is western red cedar, Thuja plicata, rather than leylandii. It is not always obvious which you have until you check the foliage. Here are the trimming questions we field on it most often.
Q. I keep seeing western red cedar recommended as a better alternative to leylandii for a boundary screen. What is actually different about it from a trimming point of view?
A. The critical difference is that thuja will regenerate from old wood, whereas leylandii will not. With leylandii, cut back past the green outer layer into the bare brown wood and that face stays brown permanently. With thuja, old wood that is cut back will, given time, push new growth. That changes the stakes considerably. A badly managed leylandii hedge can reach a point where it genuinely cannot be fixed without taking it out; a badly managed thuja hedge can usually be recovered over two or three seasons, given the right approach. For the leylandii-specific picture, our leylandii reduction Q&A covers staged reductions, why one-visit hard cuts fail, and what it costs to put one right.
Q. When is the right time to trim a mature thuja hedge, and how many times a year?
A. Twice a year for a mature hedge that you want to keep compact: once in late May or June, and again in August through to late September. The second cut is the more critical timing-wise, because fresh new growth pushed after late September will not harden before the first autumn frosts and you end up with soft, browning tips without having done anything else wrong. Some of the more sheltered valley-floor plots down towards Wouldham and Burham can push the September cut a little later, but I would not count on it. While the hedge is still young and growing to height, one cut a year in September is usually enough.
Q. I want to tidy mine up in April. Is there a reason not to?
A. The nesting season is the reason. Section 1 of the Wildlife and Countryside Act 1981 makes it an offence to damage or destroy the active nest of any wild bird while it is in use or being built, with an unlimited fine and up to six months in prison on conviction. Western red cedar is exactly the type of dense, layered evergreen conifer that wrens, dunnocks and robins favour for nesting, from March through into June. The Act does not fix a calendar window, but GOV.UK gives 1 March to 31 August as the main nesting season. A visual check of the hedge immediately before any cut is the minimum standard. April and May are not impossible windows for light routine trimming provided there is no nest activity, but they are not the time to start cutting back hard or removing material from the interior of the hedge. If in doubt, wait until September and do the cut properly then. Our hedge timing Q&A covers the nesting-season rules, the two demand peaks and the species-by-species calendar.
Q. I cut mine back too hard on one face last year and I have a panel of bare brown. Can it come back?
A. It can, and that is the honest difference between thuja and leylandii in this situation. But the recovery is slow, often two to three growing seasons before the gap fills back to a proper screen. The plant needs the adjacent green growth to be doing well and feeding the root system, so do not go heavy on the rest of the hedge while that bare panel is recovering. Keep the healthy parts trimmed lightly, make sure the base of the hedge gets water through the first dry summer after the cut, and be patient. Most thuja panels in this situation that we see on the Rochester hillside gardens and around Frindsbury do come back with enough time. The recovery is much less reliable from an exposed, desiccated face or where the rest of the hedge is also under stress.
Q. My hedge has outgrown its space and I want to reduce the height by about a metre and a half. Should I do the whole thing in one go?
A. Spread it over two seasons. The first winter, take the hedge to an intermediate height, roughly halfway to your final target, and cut the sides back to reopen the green zone. Let the plant put on a full growing season with the new cutting surface, then drop to the final agreed height the following winter. Taking a large thuja down in a single hard cut is not impossible in the way it is with leylandii, but doing everything in one year extends the recovery window and leaves you with a rough, slow-filling result for longer than most people want to live with. Two seasons gives a much cleaner outcome. If the hedge sits inside the Rochester Conservation Area and the individual stems have reached 75mm diameter at 1.5 metres, it may require a six-week notice to Medway Council under section 211 of the Town and Country Planning Act 1990 before work starts. Our conservation area Q&A covers the notice process, the 75mm test and how the six-week wait works in practice.
Q. Does thuja actually do well on chalk? I am on the higher Cuxton side and I have been told it needs richer soil.
A. That concern is mostly misplaced. Thuja plicata performs well on chalky, free-draining soils, which is exactly what you find on the higher ground above the Medway valley around Cuxton, Halling and the upper Rochester slopes. It is more particular about waterlogging than about nutrient content, and chalk gardens drain quickly, so that works in your favour. On the thinnest chalk I would add some organic matter to the planting zone to help establishment in the first two years, but a mature hedge in that ground should not be struggling because of the soil type alone. Cherry laurel is the common hedge species that genuinely dislikes thin chalk; thuja is not one to avoid on the Rochester hillside. The Medway valley clay soils suit it equally well, provided the drainage is reasonable.
Q. My hands and arms come up in a rash every time I trim the thuja. Is the plant actually causing that?
A. Yes, it is. Thuja plicata foliage is a documented skin irritant: contact with the cut surfaces and the foliage itself causes contact dermatitis in a significant proportion of people who handle it. Wear gloves and long sleeves as a matter of course, not as an occasional precaution, and add a dust mask if you are cutting a long run and working in a cloud of clippings. The rash clears up once the exposure stops, but repeated exposure without protection can increase sensitivity over time, which is why contractors who work on thuja regularly tend to be careful about kit rather than hoping for the best. Yew clippings are separately toxic if ingested, but the skin-irritation issue specific to thuja is worth knowing about before you start trimming.
If you are deciding whether western red cedar is the right species to plant in the first place, our species choice Q&A covers how it compares with yew, beech and laurel across different Rochester soils. If your hedge has gone well beyond a trim and needs a proper renovation, our overgrown hedge renovation Q&A covers the wider renovation process across species, including the honest signs that a hedge is past saving and should be replaced. If your thuja is in the Rochester Conservation Area, our conservation area Q&A explains the notice requirements and the stem-diameter test that determines whether they apply.
Need a thuja hedge quoted?
Send your postcode, a rough measurement of length and height, and what you want done to hello@rochesterhedges.co.uk, or call 07763 100 477. We will tell you honestly whether it needs one cut or two, and what the realistic timeline looks like.
Sources: Wildlife and Countryside Act 1981, section 1; Town and Country Planning Act 1990, section 211; RHS, Pruning hedges; Gardeners' World, How to Trim a Conifer Hedge.