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Purging buckthorn in a native hedge: include it in the species mix, or leave the slots for easier plants?

Purging buckthorn (Rhamnus cathartica) turns up in old east Kent hedgerows more than most people realise, and for good reason. It is a genuine chalk-country native, it is brutally thorny, and it is the sole larval foodplant of the brimstone butterfly alongside alder buckthorn. When you are specifying a new native field-boundary hedge on the chalky boulder clay around Goodnestone or Chillenden, the question is not whether buckthorn is ecologically worthwhile. It clearly is. The question is whether the real disadvantages, including its role as an alternate host for oat crown rust and the sheer awkwardness of managing a mature specimen, outweigh the gains for your particular boundary and its neighbours' land use.

What purging buckthorn is in a hedgerow context

Rhamnus cathartica is a native deciduous shrub found naturally across the chalk and limestone belts of south-east England, including the hedgerows between Goodnestone, Chillenden, Knowlton and out towards Wingham. It prefers calcareous, free-draining soils: the chalky boulder clay here suits it considerably better than the heavier clay of the Weald to the west. Left unmanaged it will reach 5 to 8 metres, occasionally taller, with a stiff, much-branched structure. The shoots end in sharp spines. The berries ripen to glossy black in late September and October and are strongly laxative: the name "purging" is literal, and the berries are toxic to humans in any quantity. Both features matter when you are deciding where in a boundary this plant belongs.

Purging buckthorn is dioecious: male and female flowers are carried on separate plants. Only female plants produce berries. Young bare-root whips cannot reliably be sexed at purchase, so if berry production for birds is a goal, you need to plant more than one plant and accept that some proportion of them will be male and produce no fruit. In practice, in a species-rich hedge with multiple plants, this is not a major issue, but it is worth understanding at the planning stage.

The decision: include purging buckthorn or leave it out?

Pros of including purging buckthorn in the mix

• It is the natural choice for chalky soil in this area. Rhamnus cathartica is a native of calcareous scrub and hedgerow in lowland England. The chalky boulder clay around Goodnestone and Chillenden is exactly the ground this species evolved for. On the free-draining alkaline soils here, establishment is reliable where hawthorn and blackthorn also establish well. There is no need to amend the soil or provide special conditions.
• It is the sole larval foodplant of the brimstone butterfly, alongside alder buckthorn. The brimstone (Gonepteryx rhamni) is one of the longest-lived British butterflies and one of the most visible early signs of spring in east Kent hedgerows. Its caterpillars feed only on purging buckthorn and alder buckthorn: without one or both of those plants in the landscape, the butterfly cannot complete its life cycle. Including even one or two well-grown buckthorn in a field boundary directly supports a butterfly population that has no alternative. Alder buckthorn prefers wetter, more acidic ground and is not well suited to the chalk here, so purging buckthorn is the species to plant for this purpose in this area.
• The structure is excellent for a stock-proof boundary. Purging buckthorn is stiff, densely branched and armed with spines at the shoot tips. A mature specimen in a hedgerow is as near impenetrable as any native shrub, more so than hazel, elder or even field maple. For a boundary that needs to hold cattle or manage access, buckthorn adds real structural value once it reaches a useful size.
• The berries are taken by blackbirds, thrushes and other frugivorous birds in autumn, providing a food source into October. The berry crop is large when conditions suit, and on a farm boundary where sloe, crab apple and rose hips are already present, a few buckthorn plants extend the autumn fruiting sequence and broaden the ecological offer of the hedge without duplicating what hawthorn already does.
• It qualifies as a native species for Countryside Stewardship and hedgerow assessment purposes. Under the Hedgerow Regulations 1997 ecological criteria and under Countryside Stewardship species-diversity assessments, Rhamnus cathartica in a hedge contributes to native species count. In an area where hedges may border farmland eligible for Higher Tier or Mid Tier agri-environment agreements, increasing species diversity is worth considering at planting time.

Cons of including purging buckthorn in the mix

• It is the alternate host of crown rust (Puccinia coronata), the major foliar disease of UK oats. The Agriculture and Horticulture Development Board (AHDB) documents the disease cycle clearly: the rust overwinters on crop debris, and in spring produces spores that infect purging buckthorn and alder buckthorn; the subsequent infection stage then reinfects cereal crops. On susceptible oat varieties, yield losses of 10 to 20 per cent are typical in a bad year. The risk is not theoretical. If the boundary you are planting runs alongside or near a field growing oats, and the farm does not grow resistant varieties, adding buckthorn to your hedge is a direct agricultural concern for your neighbour. This is the most serious practical objection to planting it near arable land in this area, and it is worth speaking to the adjacent landowner before you proceed. For a garden boundary in the village, away from arable ground, the rust risk is not an issue.
• A mature specimen is difficult and unpleasant to manage. The spines are not like hawthorn spines, which are stiff but localised. Buckthorn produces thorns along the whole shoot structure. Working with it at close quarters when renovating or cutting back requires heavy gloves and long sleeves, and mechanical flailing is the practical way to manage it in the field, the same as you would handle blackthorn. If your boundary is one you manage by hand, or one that runs close to a footpath or bridleway where overhang onto people matters, factor in that annual maintenance will be more demanding than the same work on hazel or field maple.
• It grows large and will exceed the managed hedge height if not monitored. Uncut, purging buckthorn reaches 5 to 8 metres. In a hedge held at 2 to 3 metres by annual or biennial cutting, it can be kept within that height, but it requires consistent attention. A section of boundary that goes uncut for two or three seasons will produce buckthorn that is significantly taller than the rest of the line and difficult to cut back hard without losing the season's berry and leaf growth. Unlike hawthorn, which breaks freely from old wood after hard cutting, buckthorn cut back to thick stems can be slow to regenerate and may produce an ugly gap in the hedge face.
• The berries are toxic, and the plant can affect livestock if leaves or berries are accessible. The laxative compounds in the berries and bark are not present at dangerous levels when the plant is within a properly managed stock-proof hedge, but if there is a realistic risk of cattle, horses or sheep breaking through and browsing the hedge from the field side, the position of buckthorn plants within the run is worth thinking about. It does not need to disqualify the species, but it is a factor if the boundary is an internal field division rather than a road frontage.

The recommendation: plant it, but be selective about where

For a garden boundary in Goodnestone village, or a field boundary that borders woodland, a lane or a non-arable use, I include purging buckthorn as a deliberate constituent of the species mix at a rate of around one plant per 8 to 12 metres of hedge run. It earns its place through the brimstone butterfly connection alone, and on chalk soil the establishment is straightforward. Plan its position away from any gate or point where the hedge gets cut back hard by a tractor.

For a boundary bordering or close to an oat-growing field, speak to the adjacent landowner first. If they grow oats and are not using a resistant variety, the objection is real and reasonable. In that situation, omit buckthorn from the sections of run nearest the oat field, and use the slot for a wayfaring tree, crab apple or an additional hawthorn instead. A few plants further along the run, away from the crop boundary, remain a reasonable compromise: the risk falls sharply with distance from the infected host.

For a run managed entirely by hand along a footpath or bridleway, I am more cautious. The maintenance overhead of a few mature buckthorn plants in a tightly managed run is real. In that case I substitute alder buckthorn if the ground has any tendency to hold moisture, or simply accept that the brimstone butterfly will be served by buckthorn elsewhere in the parish's hedgerow network.

Planting notes for the Goodnestone area this autumn

Bare-root purging buckthorn whips are available from October and can be planted through to March. On the chalky boulder clay here, plant into soil that has softened after autumn rain, ideally from mid-October onwards. The species establishes readily on this ground without soil amendment. Use a 60 cm spiral guard and 1.2 m cane per plant, as you would for any thorny species at risk from rabbits: the rabbit population on the chalk farmland around Goodnestone will take young whips if they are left unguarded, and buckthorn at 40 to 60 cm is just as vulnerable as hawthorn. A 5 cm woodchip mulch ring kept clear of the stem, extending to about 50 cm radius, reduces competition from grass in the first two growing seasons and pays for itself in first-year growth rate.

At purchase, bare-root buckthorn is typically sold as mixed-sex material. If you want to maximise berry production, plant in groups of three or more rather than as single isolated specimens, which improves the chance of having at least one female in each group. In the species mix I use for a new native hedge on the chalk here, purging buckthorn comes after hawthorn, blackthorn, hazel and field maple in priority order, but ahead of dogwood and elder, because of its greater structural value and the brimstone link that nothing else in the mix replaces.

Sources: Woodland Trust, species guide for Rhamnus cathartica and hedgerow planting guidance; Agriculture and Horticulture Development Board (AHDB), symptoms and management of crown rust, the major disease of UK oats; Wildlife Trusts, purging buckthorn species profile; Habitat Aid, Rhamnus cathartica cultivation and ecology notes; Wildlife and Countryside Act 1981, section 1; Hedgerow Regulations 1997 (Schedule 1, ecological criteria); checked against current sources on Rhamnus cathartica ecology and distribution in south-east England.