The charity is asking people to raise sponsorship for wearing wellington boots on walks and to wear wellies to work or school on April Fool's Day.
It aims to raise awareness about its work protecting the environment and promoting organic produce by playing on the gardening associations of wellies.
Welly-wearers will also be encouraged to 'get outdoors and enjoy the environment' during the organisation's first-ever Welly Week, which runs from 27 March to 3 April.
'The welly theme was chosen because the welly is a recognised symbol of outdoor life and has a fun, accessible image - plus nearly everyone has a pair so they can all get involved,' said HDRA PR officer Sarah Tyrrell.
Celebrities associated with gardening and farming are endorsing the campaign at fundraisers and in press releases.
Patricia Gallimore, who plays Pat in radio soap The Archers, will take part in a 'welly walk' at HDRA's Ryton Organic Gardens in Warwickshire, while Blue Peter gardener Chris Collins will launch an event at Yalding Organic Gardens in Kent.
National, women's, lifestyle and leisure media are being targeted, along with gardening, environmental and relevant regional press.
The organisation intends to use the campaign to reach out to new audiences.
'As well as our 31,000 members, we want to attract the interest of individuals, families, schools and businesses who may not have even heard of HDRA, but are keen to help the environment and have fun at the same time,' said Tyrrell.