Plant health and biosecurity in a planting specification

Biosecurity has moved from the back of a planting specification to the front of it, and councils now condition it. The reason is straightforward: a development that imports several hundred nursery trees is a pathway for pests and pathogens, and a scheme whose landscape planting dies of a disease brought in with the stock has failed its own biodiversity commitments. A specification that names species, stock size and root condition but says nothing about sourcing, plant passports and site hygiene is incomplete.

Why biosecurity now appears in planning conditions

Two things drove the change. The arrival of pests and pathogens that were not here a generation ago, and the recognition that nursery stock movement is how most of them travelled.

Ash dieback removed a species from planting schedules across the country. Phytophthora species, oak processionary moth and spruce bark beetle have each produced statutory controls in specific areas. And the plant health regime itself changed, with a Great Britain plant passport system operating since the beginning of 2021 and separate requirements for imports.

The practical consequence for a developer is that a landscape condition can now legitimately require more than a plant list. Authorities increasingly ask for a sourcing statement, retention of plant passports, a biosecurity method statement, and species diversity limits within a planting mix. Those are reasonable requirements and they cost little to meet if they are planned for. They are expensive if they arrive after the nursery order is placed.

Plant passports and nursery documentation

A plant passport is the document that travels with plants for planting moving within Great Britain, issued by the authorised professional operator supplying them. It records the botanical name, the traceability code and the operator's registration, and for certain species and destinations it carries additional declarations.

Three practical points for a site team.

Passports are issued to the buyer and have to be kept. Where a condition requires retention, the requirement is usually for the passports to be available for inspection for a period after planting, so file them with the delivery notes rather than discarding them with the packaging.

Imported stock arrives under a phytosanitary certificate from the exporting country and is then passported for onward movement in Great Britain. The certificate is the document that shows where the plant actually came from, and it is worth asking for.

Trade in oak within and around the designated oak processionary moth management areas is subject to specific movement requirements. If your scheme includes oak and sits in or near the south-east, ask the nursery to confirm the position in writing before ordering, because the controls change as the affected area changes.

Where a scheme is delivering habitat creation for biodiversity net gain, the planting has to survive the thirty-year management period, so the sourcing evidence belongs in the same file as the Biodiversity Net Gain Assessment.

Sourcing, provenance and quarantine periods

Three separate questions get conflated here, and separating them makes a specification much easier to write.

Where the plant was grown is a biosecurity question. Stock grown in Great Britain from seed or cuttings, without an overseas growing-on stage, carries the lowest risk of importing something new. The Plant Healthy certification scheme and the UK and Ireland Sourced and Grown assurance offer a way of evidencing that, and naming one of them in a specification is more useful than the phrase "UK sourced", which a nursery can satisfy with stock grown abroad and finished here.

Where the seed came from is a provenance question, and it matters for habitat creation rather than for biosecurity. Native species of local provenance are better adapted and are normally what an ecologist specifies for hedgerow and woodland planting.

Whether to hold imported stock before planting is a risk management question. A holding or quarantine area, separated from existing planting and from the new planting areas, with the stock inspected over a growing season before it goes in, is the standard answer where imported stock cannot be avoided. It needs space, irrigation and someone to look at it, so it has to be planned into the site logistics rather than improvised.

Lead time is the real constraint behind all of this. Contract-grown stock of any size takes two to three growing seasons, so a specification requiring British-grown semi-mature trees placed six weeks before planting cannot be met. Order early or specify smaller stock.

Species diversity as a disease resilience measure

A monoculture avenue is one disease away from being a bare street. That is not a hypothetical: it has happened twice in living memory in Britain, with elm and then with ash.

The resilience approach is a diversity rule within the mix, and several authorities now condition one. A common formulation caps the proportion of any single species, and sometimes of any single genus and family, within the total planting. It is a sensible requirement and the numbers should be agreed rather than imposed, because a small scheme with twelve trees cannot meet a cap designed for two hundred.

Diversity has to be reconciled with the other aims of the planting, and there is a genuine tension. Ecologists want native species of local provenance. Urban designers want a consistent street character. Highway engineers want species that will not lift a footway. A cap on any one species pushes against all three, and the honest answer is that the mix is a compromise which should be explained in the Landscape Strategy rather than presented as optimal.

Avoid specifying anything listed in Schedule 9 to the Wildlife and Countryside Act 1981, since it is an offence to plant or otherwise cause to grow in the wild those plants, and some are still sold.

Bare root against containerised stock

The choice affects biosecurity risk, planting window, cost and establishment, and the four do not point the same way.

Bare root is the lower-risk and lower-cost option for hedgerow, woodland and whip planting, and it establishes well. Its constraint is the dormant window, which means the planting has to be programmed rather than fitted around the last of the construction works.

Containerised stock buys flexibility in the programme at the cost of a larger volume of growing medium arriving on site, which is the main pathway for soil-borne Phytophthora species. Where containerised stock is used, inspect the root balls on delivery, reject anything with a bad smell or blackened roots, and keep the water source for irrigation clean.

The programme point is worth stating plainly to a client. Choosing bare root and then failing to reach the planting areas before the end of March costs a year, and the stock size and establishment requirements in the condition still have to be met, as our note on tree planting conditions: species, stock size and establishment explains.

Site hygiene during planting

Most of this costs very little, and it is the part most often omitted from a method statement.

Clean boots and tools between planting areas, with a disinfection point at the entry to each. Clean machinery arriving on site, particularly tracked plant that has come from another planting job. Keep soil movement between areas to a minimum, and do not move soil from an area with known plant health problems at all.

Manage water. Irrigation drawn from a watercourse or a site pond can carry Phytophthora, and a clean mains or tanked supply is preferable for newly planted stock. Standing water in a holding area is a risk in itself.

Handle green waste properly. Prunings, failed stock and packaging from a planting operation should be removed or composted away from planting areas, not stacked at the edge of the new woodland.

And record the inspections. A dated log of deliveries inspected, stock rejected and hygiene measures applied is what evidences compliance when the condition is discharged. Where planting sits next to sensitive habitat, the buffer requirements interact, as our piece on ancient woodland buffers on a development site sets out.

Wording a condition that can actually be met

The conditions that work require a document and a record. The ones that fail require an absolute sourcing outcome.

A workable condition asks for a planting specification and biosecurity method statement to be submitted and approved before planting, covering species and quantities, stock size and root condition, the sourcing hierarchy with evidence of the steps taken, plant passport retention, a holding and inspection regime for any imported stock, site hygiene measures, and a species diversity cap agreed for the scheme size.

An unworkable condition requires all stock to be British grown and certified, with no fallback. Availability of specific species and sizes fluctuates, and a condition with no alternative route forces either a non-compliant planting or a variation application. Offer the sourcing hierarchy instead: certified British-grown first, British-grown second, and imported with a holding and inspection regime only where the first two cannot supply, with the reason recorded.

The condition should also say when it is discharged. Tie it to the completion of planting with the records submitted, rather than leaving it open, and check the wording against the Arboricultural Impact Assessment so the two documents do not contradict each other.

PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval. Councils usually expect landscape and arboricultural documents to have a suitably qualified author, so professional review is strongly advised.

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