RHS Gardens for our Future: Water

Cambridge Conservation Dr M. Maunder, RHS Environmental Hort. Dr M. Gush, Met Office Dr F. Garry, Wisley S. Das & designer T. Massey.

Photo by Nadiia Ploshchenko 🇺🇦 on Unsplash

Water, Boom or Bust

Sustainable water management

As summers become hotter and drier, winters are becoming warmer and wetter. “We saw 40mm of rain in three hours,” said Dr. Freya Garry when speaking about the recent storm Babet. Extreme rainfall (in summer and winter) can cause dangerous flash floods, which are happening with increasing frequency. The 23 million UK gardens and cultivated landscapes represent a significant resource to mitigate the risks of flooding.

Sustainable water management within gardens and parks, could be part of the way forward to build resilience to climate variability and extreme weather conditions, which comes down to;

(1) The collection and storage of rainwater – water butts and/or reservoirs. The latter could also be designed to function as an aquatic habitat to enhance biodiversity (and even to generate power through floating solar panels).

(2) Minimising rainwater runoff and maximising absorption – rebuilding the vegetation to slow the flow of water. Tree planting regulates the flow of water as the leaf canopy intercepts rainfall, slowing its fall to the ground and ensuring water absorption.

The panel advised gardeners to investigate where the water goes during heavy rainfalls, to ascertain where intervention may be needed. Hard surfaces may need to be de-paved to make way for more permeable options. Similarly, working with neighbouring properties as gardens form part of a broader community.

The 2024 RHS Flood Resistant Garden designed by Naomi Slade and Ed Barnsley is an example of a garden designed to cope with the challenges of heavy rain and surface flooding by embracing water as a feature, and harnessing it for later use.

(3) Maximising soil health to improve retention as well as drainage – Mulching and composting borders increases the water holding capacity of soil and facilitates slower drainage into the soil. The RHS are researching fungal hyphae and soil bacterial cells which bind the soil to create water-stable aggregates that enhance water retention and drainage.

(4) Selection of the right plants for site conditions. Selection of plants for purpose to harness the power of plant diversity. The RHS is conducting research to understand which plants provide the most suitable ecosystem service benefits such as water uptake and carbon sequestration.

When it comes to trees in areas of flooding, Tom Massey added that Alder trees are able to absorb nitrogen and toxic heavy metals from the ground via root nodules to improve soil health and fertility. Furthermore, Alder wood is soft and porous but extremely durable when wet, making it ideal for areas experiencing frequent flooding. Massey’s 2024 RHS Chelsea WaterAid Garden, features plants and trees (including Alders) that can cope with varying amounts of water.

Mains to Rains

In association with Cranfield University, the RHS started Mains2Rains in 2021 which invites pledges from gardeners to stimulate sustainable water management with the aim to switch from mains to rainwater usage. To date, the project has received 3384 pledges which according to Dr. Mark Rush equates to a potential saving of 40 million litres of water.