Extreme weeding – fighting an aquatic invader at Claremont

In an extreme case of weeding, amphibious tractors are this week tackling almost 16 tonnes of invasive weed in the lake at the National Trust’s Claremont Landscape Garden.

The vehicles, an amphibious cross between a tractor and a tank, are armed with giant rakes to remove the carpet of Crassula helmsii – also known as New Zealand Pigmyweed – that is covering the man-made serpentine lake at the Surrey garden.

Extreme weeding at Claremont, photo Dee Durham/National Trust

The non-native weed reproduces rapidly and, without natural competition in the UK, can quickly spread out of control, overtaking a waterbody and blocking out light for other flora and fauna.

The harvesters have been busy collecting the weed and depositing it in a huge pile on the island in the centre of the lake. Here it will rot down quickly, creating compost, while allowing any fish and invertebrates scooped up to make their way back into the lake.

The lake is 27,000 m2 and it could take almost two weeks for the surface to be completely clear of the aquatic invader. There is currently no known way to entirely eradicate the weed, so gardeners at Claremont will manually remove the weed throughout the year using nets and waders. 

Claremont Landscape Garden, photo Hannah Elliott/National Trust

Tim Rayfield, Senior Gardener at Claremont, said: “By using the large harvesters, we’re able to control the Crassula with minimum impact on the lake and its eco system.

“It’s one of the more unusual ways that we conserve this amazing landscape garden, and it’s great to be able to see the trees reflected in the water once again.”

 

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