Hybrid SuDS Planters: An innovative solution for shallow dig Rain Gardens

16th October 2025

Read time 3 min

How to overcome depth constraints in Urban Drainage: Hybrid SuDS Planters as a Rain Garden Alternative

The expansion of urban infrastructure has made below-ground space increasingly complex and utility services and hard surfacing often prevent the installation of traditional rain gardens. With there now being over 4 million kilometres of underground services in the UK, finding new ways of overcoming the need to dig for Sustainable Drainage System in urban spaces is very important.

At Meristem Design, we have developed an alternative: the Hybrid SuDS Planter - a system that integrates sustainable drainage and planting within a shallow profile.

Design Challenge

The aim was to create a functional and aesthetic SuDS solution that could be implemented when there are restrictions on-site. For example, at Redlees Park in the London Borough of Hounslow, our task was to introduce a welcoming, flood-resilient entrance to the park. However, ground conditions restricted excavation depth, ruling out a standard rain garden approach.

System Design: Hybrid SuDS Planters

Meristem’s Hybrid SuDS Planters were installed as a series of ground-level, partially submerged units, each sunk 200mm into the ground. The planters feature a Hydrorock base layer that provides subsurface water storage and attenuation. Outer edges of the planters were finished with 10 mm shingle, ensuring a seamless interface for surface water flow.

A similar design was also used to deliver the Croydon Town Centre Rain Garden SuDS Planters. The large, raised powder-coated steel planters were designed with perforations, granular layers, and geotextile membranes to control water absorption and runoff.

How does the Hybrid SuDS Planter work?

Capture: Rainwater flows into the planter through inlets or from nearby paved surfaces.

Storage: The Hydrorock layer at the base holds the rainwater for a short time, stopping it from running off too quickly.

Capillary Rise: The stored water slowly moves up through the soil, keeping the plants watered.

Gradual Release: Any extra water either evaporates or drains slowly back into the local system.

This design combines the innovative technology of SuDS Planters with the design of a Rain Garden, enabling an effective performance without deep excavation, making it particularly suited to urban areas constrained by utilities, paving or tarmac.

Key Outcomes

Effective Water Management: Hydrorock attenuation slows runoff and reduces flooding risk.
Adaptable Installation: Can be integrated into soft ground, paving or tarmac.
Customisable Design: Option to incorporate trees, seating or bespoke planters.
Biodiversity and Amenity: Enhances ecological value and public realm quality.

A Model for Future SuDS Design

Hybrid SuDS Planters demonstrate how SuDS technology can evolve to meet modern urban constraints. By merging rain garden functionality with modular, surface-level SuDS Planter infrastructure, this system provides a scalable, low-maintenance approach to flood mitigation and landscape enhancement - especially valuable where excavation depth or underground utilities limit conventional solutions.