Plant selection and specification with Nick Coslett

Plant Selection & Specification: Designing Resilient Landscapes for a Changing World

In an era where over 50% of the world’s population now lives in urban environments — and in the UK, that figure climbs to 80% — reconnecting people with the natural world has become one of the most pressing and powerful responsibilities for landscape architects, designers, and urban planners.

Choosing the right plants for a landscape isn’t just about aesthetics. It’s about climate resilience, biodiversity support, urban health, and future-proofing our green spaces. From towering urban trees to wildflower meadows, every plant in a designed space plays a role in environmental health and human wellbeing.

Climate Change, Ecology & The Role of Plants

It’s sobering to realise that wild animals now make up only 40% of the Earth’s animal population — and wild birds even less, with a significant portion of them domesticated species like chickens. Our modern cities and lifestyles have increasingly disconnected people from the natural world.

Urban greening isn’t just desirable, it’s necessary. Green infrastructure reduces the urban heat island effect, improves air quality, manages rainwater, and provides vital habitats for pollinators and birds.

Urban trees in particular offer:

• Shade and cooling

• Carbon capture and air purification

• Biodiversity enhancement

• Improved mental health and wellbeing

• Stormwater management through interception and absorption

• Tree planting is one of the single most valuable investments a landscape project can make

Plant Selection: The Fundamentals

Good plant selection begins with understanding:

• Climate change projections and choosing resilient species

• Soil type and drainage

• Exposure to wind, sun, and shade

• Habitat creation potential

• Maintenance capacity and client expectations

• Plant substitution is common when availability or site conditions change, but clear communication is key — misunderstandings can lead to classic “four candles” moments (look it up for a laugh if you haven’t seen the famous Two Ronnies sketch)

Tree selection terms:

• Whip: 60-120cm young trees

• Feathered: Multiple side branches along the stem

• Standard: 8-10cm girth at 1m height

• Selected Standard: 10-12cm

• Heavy Standard: 14-16cm

• Extra Heavy Standard: 16-18cm+

• Pleached trees: Trained flat framework of branches

• Espalier trees: Trained against walls or fences

• Always reference the National Plant Specification for accurate plant descriptions

Planting, Establishment & Maintenance

Tree establishment is critical — and surprisingly, around 25% of newly planted trees fail. Poor maintenance in the first two years is the main culprit.

Key planting tips:

• Water young trees April to July

• Use gator bags or irrigation systems

• Square tree pits encourage roots to break out corners

• Dig only to the depth of the rootball

• Position at the basal flare for stability

• Handle plants minimally during transport

Root types:

Bare root: Nov-March

Rootball: Mid-Oct to Mid-April

Container-grown: Year-round

Biosecurity matters. Imported pests and diseases like Ash Dieback, Oak Processionary Moth, and the deadly Xylella fastidiosa are serious threats. Use suppliers with Plant Passports and phytosanitary certification. Check planthealthy.org.uk and the UK Plant Health Risk Register.

The 30:20:10 rule for planting diversity is key:

• 30% from the same family

• 20% from the same genus

• 10% of the same species

• This reduces vulnerability to pests and disease outbreaks

Shrubs, Perennials & Bulbs

Shrubs and perennials, typically pot-grown, are generally available year-round — though availability can fluctuate. Bulbs are sold by size and planted in bulk by machines (up to 20,000 per hour!) to create year-long flowering schemes from February to July. Pot sizes are typically in the 8cm to 10L range, with a growing shift toward recyclable pots and peat-free growing mediums to improve sustainability.

Soil Health, Fungi & Tree Resilience

Soil quality is vital. Mycorrhizal fungi support plant health by forming symbiotic relationships with roots, improving nutrient uptake and stress tolerance — especially useful in harsher urban soils. Sprinkle these at planting to support establishment, especially in poor or compacted soils.

Disease Risks & Future-Proofing

The climate crisis will challenge our plant choices. Native species are essential for biodiversity, but climate migration of species is happening too. Quercus robur (English Oak), for instance, is seeing its range shift.

Constant monitoring for new threats is crucial. The UK risk register currently lists 1,410 plant hazards, and urban tree managers need to stay vigilant.

Final Thoughts

Plant selection and specification is as much about people and place as it is about botany. In an urbanised world, designed landscapes offer some of the last frontiers for meaningful biodiversity and climate action.