More than 5,000 volunteers will create a ‘river of green' across the country in a bid to boost biodiversity.
Events begin tomorrow (24 March) as school children, volunteers and commuters from across London will plant wildlife-friendly shrubs at Tower Hill Gardens, between 7:30am and 1:00pm.
The event will be co-hosted by City of London in Bloom, one of this year's Britain in Bloom finalist communities.
More than 60 Britain in Bloom groups will continue the mass planting over the weekend (27-28 March) with a series of gardening and biodiversity oriented events.
RHS community horticulture manager Stephanie Eynon said: "RHS Britain in Bloom brings people together through long-term, sustainable projects which are also hugely beneficial to the environment.
"Each year around 2,000 communities are involved in the campaign, cleaning up and greening up their area. Participating communities range from next door neighbours and blocks of flats all the way to urban communities and large cities. These communities reap rewards of not only cleaner and greener spaces but also safer and more cohesive communities."
For more information on RHS Britain in Bloom visit www.rhs.org.uk/britaininbloom