Crassula clear out

A close up of crassula, tiny thick leaves with little white flowers.

Crassula (credit: Philip Precey)

In 2024, Norfolk Wildlife Trust received funding from the Anglian Water Invasive Non-Native Species Fund to help stop the spread of the invasive pond plant, Crassula helmsii in South Norfolk. This will reduce the threat the species poses to pond-loving plants and animals including frogs, newts and dragonflies.

Part of the project involves eliminating the plant from two sites in South Norfolk, which will protect them from the spread of Crassula from a small number of currently affected ponds to large numbers of ponds that are of high value for wildlife.

We also aim to build knowledge and skills in local landowners, volunteers, contractors and conservation professionals to identify and eradicate Crassula across the area.

This two-year project will build on work led by NWT Crassula Officer, Julia Mumford-Smith, who has successfully removed Crassula at our Thompson Common nature reserve. This work has protected the site’s rare pingo ponds and the plants and animals that rely on these unique landscape features and was generously funded by the Anglian Water Invasive Non-Native Species Fund and the Natural England Species Recovery Programme.

What is Crassula?

Crassula helmsii is also known as Australian swamp stonecrop or New Zealand pygmyweed. It is an aquatic plant that was introduced to Britain in the early 20th century and by the 1950s had been reported in the wild. By 2014 the species had spread so much it was found in thousands of UK waterbodies and was banned from sale in the UK.

Why is Crassula a problem in Norfolk?

Norfolk is home to a very high proportion of UK ponds, and South Norfolk is a stronghold for pond-loving species such as the great crested newt. This makes it particularly important to tackle Crassula in this area.

Crassula grows throughout the year, without a dormant period, and can form dense mats on waterbodies such as ponds and ditches that shade and smother other aquatic vegetation that provides creatures such as frogs, newts and dragonflies a place to hide, feed and lay eggs.

The species is very hard to control and can spread quickly from tiny fragments which can drift in the water or be carried on clothing or animals, including humans, dogs, birds or deer.

Protecting ponds at Mulbarton Common and Earsham Estate

We will use, and share, this accumulated knowledge as we work alongside landowners at Mulbarton Common and Earsham Estate to tackle Crassula in ponds at two wildlife-rich sites in South Norfolk.

The South Norfolk Claylands is a hugely valuable area for ponds, and Crassula presents a big risk to the biodiversity of the area. At both project sites the majority of ponds are Crassula-free but there are some ponds with the species present. The aim is to remove Crassula from the infested ponds before it can spread to the rest of the ponds on these wildlife-rich sites.

Volunteers and NWT staff will be trained in tried and tested Crassula survey and removal techniques as well as best practice biosecurity methods. Together, we will survey and remove the plant from 26 ponds across the two sites.

Protecting the wider landscape

We will publish best practice guidance on Crassula survey and removal and host a Norfolk Ponds Conference in spring 2026. By bringing together landowners, contractors, community groups, councils and practitioners together, we will help to broaden knowledge of Crassula and proven techniques for removing it from our ponds.

A project pond showing a matt of crassula present in the water.

Crassula present in a project pond

Crassula forming a mat threatening a project pond

A pond in South Norfolk surrounded by vegetation and autumnal trees.

Ponds are a huge part of the South Norfolk landscape

Three people gathering around a pond during the winter.

Surveying a project pond

Volunteering opportunities

We'll be training volunteers to identify, survey and successfully remove Crassula from infested ponds. Training sessions will be held in Mulbarton and Earsham in March and April 2025 and volunteers will be coordinated to undertake site surveys and tackle Crassula from spring 2025 until autumn 2026.

If you are interested in being involved as a project volunteer, or would like more information, please contact Ben Newton, NWT Wilder Landscapes Adviser: benn@norfolkwildlifetrust.org.uk