Brown patches on a conifer hedge: four causes and how to tell them apart.
A browning conifer hedge has four possible culprits, and the right response to each is completely different. Working out which one you have takes five minutes and saves you treating the wrong problem.
Conifer hedges across the Wingham round, primarily Leyland cypress (x Cuprocyparis leylandii), Lawson's cypress (Chamaecyparis lawsoniana) and Western red cedar (Thuja plicata), are hardy enough plants, but they go brown for reasons that are genuinely hard to tell apart from a distance. The wrong call is expensive. Spray for aphids when the real cause is drought and you waste money and harm beneficial insects. Assume you can fill the patch with new growth when the problem is a hard trim into old wood, and you will wait forever. The four causes each leave a pattern on the hedge. This guide is a decision tree for reading that pattern.
East Kent matters here because it is one of the drier parts of England. The nearest Met Office station, Manston, averages about 610 mm of rain a year (1991-2020). That changes the way you read browning symptoms: drought stress is much more likely to be a contributing factor here than in wetter parts of the UK, and it can mask or be mistaken for cypress aphid damage. On the free-draining chalk west of Wingham toward Adisham and Bekesbourne, where topsoils are thin and moisture is gone quickly in July and August, this complication is at its sharpest.
Cause 1: Cypress aphid
Cypress aphid (Cinara cupressivora and related species) is the most common cause of brown patches on conifer hedges in UK gardens. The RHS, working with East Malling Research, found aphids associated with around half the cases of brown patches they investigated.
The pattern is characteristic. Browning starts in the lower interior sections of the hedge, often at the base, and is patchy rather than uniform across a face. It appears from late spring into summer, but the hedge may not show it clearly until the aphids have long gone, because the damage takes weeks to become visible. The key diagnostic sign: tap a brown branch over a sheet of white paper in spring or early summer. Falling cast skins or tiny dark insects confirm aphids. A black powdery coating of sooty mould on the stems, caused by honeydew the aphids excrete, is another pointer.
Aphids do not eat old wood; they suck sap from living stem tissue. If the browning is inside the hedge where it never gets any sun or airflow, and the outer green face is still intact, cypress aphid is the most likely cause.
What to do: In most cases nothing immediate, unless damage is severe and the hedge is recently established. Healthy established conifers will regrow from nearby live growth slowly over one to three seasons. If the infestation is confirmed and active in spring, contact insecticides labelled for aphids are available; apply outside the peak bee-foraging period (early morning or evening). Once the green foliage adjacent to the affected patch is growing, it will gradually close the gap. Raking up the fallen leaf litter at the base of the hedge each autumn removes some of the overwintering eggs and reduces pressure the following spring.
Cause 2: Summer drought stress
On the chalk soils west of Wingham, drought stress in late summer is a common cause of conifer browning that is frequently misdiagnosed as aphid damage or cutting injury. The shallow, free-draining chalk between Wingham village and Adisham gives conifers a very limited moisture reserve. In a dry July or early August (a long spell without significant rain), Leyland cypress and Lawson's cypress on chalk will show tip browning on their most exposed faces, particularly the south- and south-west-facing sides that get the most afternoon sun.
The pattern is different from aphid damage: browning is on the outer tips of the sunniest faces, not in the shaded interior base. It is more uniform across the affected face and shows up after a dry spell rather than in a single patch. The rest of the hedge may still look perfectly green.
Soil matters: thin, free-draining ground dries out fastest, so conifers on it tend to show drought browning first, while deeper soil holds more moisture through a dry spell. The difference matters most in the driest years.
What to do: A deep, infrequent soak (10 to 15 litres per plant, once or twice a week during dry spells) is more effective than a daily trickle: deep watering encourages roots downward while a surface trickle keeps roots shallow and more vulnerable to the next dry spell. A 7 to 10 cm mulch layer at the hedge base, kept 5 cm clear of the main stems, reduces moisture evaporation significantly on chalk ground and is worth applying every autumn. Brown tips from drought stress usually resolve in the following season once growth resumes and the live foliage closes over the damaged area.
Cause 3: Cutting into old wood
This is the permanent one. Leyland cypress, Lawson's cypress and Western red cedar will not regrow from old, brown, leafless wood. The green live zone on a mature hedge is only the outermost 15 to 30 cm of the foliage. If a trimmer cuts past that zone into the brown interior, that section will stay brown indefinitely.
The pattern is unmistakable once you know to look: browning appears exactly where the cut surface is, in a flat plane that corresponds precisely to the cut line. There is no sooty mould, no pattern of lower-base severity, no directional drought bias. The cut face is brown and the area behind it is brown, and both were brown within days of the cut rather than weeks or months later.
This is covered in detail in the staged leylandii reduction guide and the Western red cedar trimming guide. The short version: on Leyland cypress, Lawson's cypress and thuja, never cut deeper than the live green layer. If the hedge has grown to a width where a single cut can only be made into old wood, reduce it over three winters, taking a few centimetres each time, not all at once.
What to do: Nothing will regrow the affected area on a Leyland cypress or Lawson's cypress. The only option is to let the adjacent live growth extend to cover it over time, which it will do slowly if the hedge is otherwise healthy. On a hedge where the entire face has been cut into old wood, replacement planting at the base is the more realistic long-term fix.
Cause 4: Root rot and waterlogging
Low-lying gardens with poor drainage are the context for this one. Gardens on low valley ground, such as along the Little Stour, are more likely to hold water than gardens on higher ground. In a wet winter, such ground can stay waterlogged for weeks. Conifers planted in low-lying ground without adequate drainage can develop root rot from soil-borne pathogens (particularly Phytophthora) that move in under waterlogged conditions.
The pattern here is patchy die-back that appears through late autumn and winter rather than summer, with entire sections of the hedge turning brown and dying from the inside out. The timing (autumn to winter, not summer) and the location (ground-level and upward, not tip-first on exposed faces) distinguish it from drought stress. Unlike cypress aphid damage, there is no sooty mould, and the browning typically affects whole lateral sections rather than interior patches.
A typical pattern is a hedge line where some plants die after a wet winter while immediate neighbours survive. That is typical of root rot reaching plants through soil contact rather than an aerial pest or uniform drought stress.
What to do: Improve drainage before replanting. A land drain or gravel sump at the hedge base can make the difference on valley-floor ground. Where the existing conifers are only moderately affected, cutting back dead sections to healthy growth and addressing the drainage issue can stabilise the hedge. Where a whole section has died, replanting with a species better suited to wet ground is the practical answer. Whatever you replant with, drainage matters more than the species.
Nesting season: 1 March to 31 August
Any remedial trimming or cutting to remove dead sections from a conifer hedge must be done outside the bird nesting season where possible. Section 1 of the Wildlife and Countryside Act 1981 makes it an offence to intentionally or recklessly damage or destroy a wild bird's nest while it is in use or being built. The Act sets no dates; the accepted guidance window is 1 March to 31 August, so the sensible window for significant work is 1 September to 28 February. Conifer hedges, even with brown patches, can still provide nesting habitat for species that will nest in semi-evergreen cover, including chaffinch and goldfinch. Before cutting dead sections during the guidance window, check that no active nests are present. Wear eye protection and gloves for any cutting work on conifer hedges. Use a long-reach pole trimmer rather than a ladder where possible; if a ladder is necessary, have someone footing it. Avoid cutting on hot, dry days in summer: cut conifer foliage desiccates faster and increases the risk of spread to healthy growth.
Common questions
Why is my conifer hedge going brown in patches?
The four main causes are cypress aphid (the most common, browning in the lower interior of the hedge from late spring), summer drought stress (tip browning on exposed faces, worst on chalk soils), cutting into old wood (permanent brown exactly where the trimmer blade went), and root rot from waterlogging (patchy die-back after a wet winter, most likely on low-lying ground near the Little Stour valley). Each cause leaves a distinct pattern and location of browning, which is the key to telling them apart.
What does cypress aphid damage look like on a Leyland cypress hedge?
Cypress aphid (Cinara cupressivora and related species) causes browning that typically starts in the lower interior sections of the hedge, often at the base, from late spring into summer. You may find a black powdery coating of sooty mould on brown stems (caused by the honeydew aphids excrete) and shed cast skins at the base of the hedge or on the foliage. The browning can appear weeks after the aphids themselves have moved on, so the absence of live insects does not rule out aphids as the cause. The RHS, working with East Malling Research, found cypress aphid associated with around half the cases of brown patches they investigated.
Does the free-draining chalk near Adisham make conifer browning worse?
Yes, in hot dry summers. The shallow, free-draining chalk west of Wingham toward Adisham and Bekesbourne gives conifers very little moisture reserve during drought. The nearest Met Office station, Manston, averages about 610 mm a year (1991-2020), which is low by English standards, so summer moisture stress is a real risk here. Drought stress produces browning on the outer tips of exposed faces, which distinguishes it from cypress aphid damage that starts in the shaded interior base.
Can a conifer hedge recover from brown patches?
It depends on the cause. Cypress aphid damage can recover if the surrounding green growth is healthy, but slowly, over one to three seasons as new foliage fills the gap. Drought stress browning on the outer tips usually resolves with better watering the following season. Cutting damage into old wood on Leyland cypress, Lawson's cypress or Western red cedar is permanent: those species will not regrow from leafless brown wood. Root rot from waterlogging depends on severity; improving drainage and removing affected sections gives the remaining hedge a chance, but the dead wood will not regenerate.
Not sure which cause you have?
Send a photo to hello@winghamhedges.co.uk or WhatsApp 07763 100 477. A description of when the browning first appeared, whether the soil is low-lying and whether you cut the hedge recently helps narrow it down quickly.
Sources: RHS, "Conifers: brown patches" advice page; RHS and East Malling Research, foliage dieback in Leyland cypress collaborative project; RHS, "Cypress aphid" (Cinara cupressivora) profile; Wildlife and Countryside Act 1981, Section 1; Met Office, Manston long-term averages 1991-2020 (checked 12 October 2026).