BNG Compliance Seeding for UK Developments
Mandatory Biodiversity Net Gain has reframed habitat creation as a planning condition that controls completion certificates, plot releases and 30-year liabilities. This page is a practical guide for developers, Tier 1 contractors, project managers and procurement leads who need to understand what BNG actually requires on site, how to commission it, and where the risk sits.
If you already know what you need delivered, send us your habitat plan or drawings and we will review access, ground conditions and seasonality.
SEEDING SPECIALISTS
BNG became mandatory for major planning applications in England on 12 February 2024 and for small sites on 2 April 2024 under Schedule 7A of the Town and Country Planning Act 1990 (inserted by the Environment Act 2021). Most developments now have to demonstrate a minimum 10% net gain in biodiversity value, calculated using the statutory Defra Biodiversity Metric and secured for at least 30 years.
In practical terms that means three obligations sit on the developer:
- A pre-commencement habitat baseline and Biodiversity Gain Plan, signed off by the Local Planning Authority before development starts.
- A delivery commitment for whichever combination of on-site, off-site and statutory credit units the plan specifies.
- A 30-year management and monitoring regime for any habitat created on site, secured through a planning obligation, conservation covenant or Section 106 agreement.
LPAs are now actively checking BNG delivery before issuing completion certificates. A Biodiversity Gain Plan that looked tidy at outline can become a programme problem at handover if the on-site habitat does not match what the Metric assumed.
If you would like to learn more, read our guide 'How to Achieve 10% Biodiversity Net Gain on a Housing Development'.
What BNG Actually Requires
The Three Routes to Compliance
BNG units can be delivered through three routes, in a strict order of preference set by statute. Most schemes end up using a combination, and the route mix is one of the earliest commercial decisions a developer has to make.
The procurement implication is straightforward. Maximising on-site delivery, where ground conditions and area allow, is almost always the cheapest and lowest-risk option, but only if the on-site habitat actually establishes to target condition. A failed wildflower meadow forces the shortfall back up the ladder into off-site units or credits, and that is where unbudgeted cost lands.
1. On-site units
Habitat created or enhanced inside the red line boundary. Cheapest per unit if the land is available, gives the developer direct control of delivery, and supports placemaking and sales narrative. Constrained by site area, soil conditions and the 30-year management commitment.
2. Off-site units
Habitat created or enhanced inside the red line boundary. Cheapest per unit if the land is available, gives the developer direct control of delivery, and supports placemaking and sales narrative. Constrained by site area, soil conditions and the 30-year management commitment.
3. Statutory biodiversity credits
Purchased from Defra as a last resort. Deliberately priced well above market rates to discourage use. Avoid where possible.
When BNG Hits Your Build Programme
BNG is not a snagging item. It has to be threaded through the programme from outline planning through to completion. The seeding window is the constraint that catches most schemes out.
The single most common BNG failure pattern we see is leaving seeding to the end of the build, missing the autumn window, sowing into a rushed spring with poor weather, and then discovering at year 2 monitoring that the habitat does not score.
Stage 1: Outline planning
Habitat baseline survey. Initial Metric calculation. Decision on on-site versus off-site mix. CDTS North & West can join these conversations to flag whether the on-site target habitats are realistic given ground conditions.
Stage 2: Reserved matters and pre-commencement
Biodiversity Gain Plan submitted and approved. Habitat Management and Monitoring Plan finalised with the ecologist. Section 106 or conservation covenant in place. This is the right point to commission the seeding contractor, not after groundworks finish.
Stage 3: Enabling works and groundworks
Topsoil management decisions made now will determine whether wildflower meadows establish or fail. Stripping fertile topsoil from BNG areas, or stockpiling it separately, costs almost nothing if planned and a great deal if forgotten.
Stage 4: Pre-handover
Seedbed preparation and seeding. Wildflower meadows need either an autumn (mid-August to early October) or spring (late March to early May) sowing window. Missing the window pushes establishment back by up to 12 months, which can delay BNG sign-off and plot releases.
Stage 5: Year 1 to Year 30
Annual cutting regime, weed control in years one and two, periodic monitoring against Metric target condition. Usually contracted to a habitat manager, with the developer carrying residual liability.
Where the Risk Sits
BNG risk is not evenly distributed. Knowing who carries what helps developers and main contractors price the work properly and write tighter sub-contracts.
The most common gap on a tender is between the main contractor and the seeding contractor, where assumptions about who is preparing the seedbed, who is managing topsoil stripping and who is supplying the seed end up unallocated. Closing that gap at pricing stage is cheaper than closing it on site.
List of Services
-
DeveloperItem Link List Item 1
Carries the planning obligation, the 30-year liability and the cost of any shortfall. Ultimate liability remains with the developer.
-
EcologistItem Link List Item 2
Owns the baseline survey, the Metric calculation, the habitat creation plan and the year 2, 5, 10 and 30 condition assessments. Liability is professional, not delivery.
-
Main contractorItem Link List Item 3
Usually responsible for protecting habitat areas during construction, executing the topsoil and substrate strategy, and instructing seeding and planting works. Often the party that absorbs programme delay if seeding is missed.
-
Seeding contractorItem Link List Item 4
Responsible for delivering the works to specification. CDTS North & West provides site records, photographs and application data so the ecologist's monitoring evidence pack is complete. Liability is for workmanship against the specification, not for whether the ecologist's habitat plan was the right one.
-
30-year managerItem Link
Often a habitat bank, land manager or LPA-approved third party. Carries the long-tail management obligation under the conservation covenant or Section 106.
SEEDING SPECIALISTS
When commissioning BNG seeding works, the following information lets a contractor price accurately and avoids variations later. If any of these are missing from your pack, ask your ecologist to supply them before going out to tender.
- The approved Biodiversity Gain Plan and the Defra Metric calculation it is built on.
- The Habitat Management and Monitoring Plan, with target NVC communities or seed mix specifications.
- Habitat parcel drawings with areas in m² or hectares, slope angles and access notes.
- A topsoil and substrate strategy, including whether topsoil is being stripped, retained or amended.
- The seeding window the works must hit.
- Required local provenance, if any.
- Confirmation of whether the site falls within an SSSI Impact Risk Zone or near any protected sites, as this affects seed mix restrictions.
- The 30-year management contract, so the seeding contractor knows what condition they are establishing the habitat into.
If you do not have all of these, that is not a problem. Please send us what you do have and we will tell you what else we need or work from there.
What to Put in Your BNG Tender Pack
How CDTS North & West Supports BNG Delivery
CDTS North & West is the seeding contractor in the chain above. We deliver the on-site works that turn an approved Biodiversity Gain Plan into established habitat, working from your ecologist's specification across the UK.
We conduct soil nutrient analysis and employ stale seedbed techniques to create the low-fertility conditions wildflowers require. This prevents invasive grasses from outcompeting native species.
1. Low-Fertility Seedbed Preparation
Our bespoke brush seed harvester (towed behind low-ground-pressure quad bikes) collects local-provenance seed from donor sites, satisfying strict ecological planning conditions.
2. Native Provenance Seed Mixes
3. Hydraulic Application for Uniform Coverage
Using our fleet of 6,000L lorry-mounted and 2,500L towed hydroseeders, we achieve even seed distribution across complex terrain, including SUDS basins, embankments, and solar farm perimeters.
For higher-value habitat (scrub/woodland), we apply direct tree seeding—a method pioneered by CDTS's founder, Alistair Luke, at Cambridge University. This achieves natural woodland establishment on hostile substrates at a fraction of traditional planting costs.
4. Woodland Creation via Direct Tree Seeding
Frequently Asked BNG Compliance Questions
Does BNG apply to my development?
If your scheme requires planning permission in England and is not on the limited exemption list (de minimis impact, householder applications, self-build), it almost certainly requires a Biodiversity Gain Plan demonstrating a minimum 10% net gain. NSIPs are expected to be brought into scope from May 2026, although implementation guidance had not been published at the time of writing. If your planning conditions reference biodiversity units, the Defra Metric or a Biodiversity Gain Plan, BNG applies.
Can we satisfy BNG entirely on site?
Sometimes, but rarely on dense urban schemes. Whether you can hit 10% on site depends on the habitat baseline, the area available within the red line, and the habitat types your ecologist can realistically establish. A brownfield site with a low baseline biodiversity value is often easier to uplift because the 10% target requires fewer new units in absolute terms. By contrast, developing on mature grassland means a higher starting value and a correspondingly larger number of units to replace and add. The Metric heavily rewards distinctive and high-condition habitats, so a small area of well-established species-rich grassland can outperform a much larger area of amenity grass. We can advise during planning on what is realistically achievable on your site.
What happens if the on-site habitat fails?
The shortfall has to be made up. In practice that means buying off-site units or, as a last resort, statutory credits, both of which are significantly more expensive than getting on-site delivery right first time. LPAs can also delay completion certificates until the gain is demonstrated. Failure modes are predictable: nutrient-rich seedbed, wrong seed mix for the soil, or seeding outside the establishment window. All three are addressable at the works package stage.
Who carries the 30-year management obligation?
The developer, secured through a Section 106 agreement, planning obligation or conservation covenant. In practice the day-to-day management is usually subcontracted to a habitat bank, land manager or specialist company. CDTS North & West does not provide the 30-year management contract, but we design and deliver habitats to minimise the intervention they need to stay in target condition.
When should BNG seeding be commissioned?
At reserved matters or pre-commencement, not after groundworks. Early engagement allows the seeding contractor to flag topsoil and substrate decisions that have to be made during enabling works, and to lock in the autumn or spring sowing window before the build programme tightens.
Discuss Your BNG Programme
Send us your Biodiversity Gain Plan, habitat drawings or planning conditions and we will review access, ground conditions and seasonality, then come back with a buildable seeding approach for your site.