The event features a gardening day in St James's Park on 1 September, followed by a local Dig Together Day weekend on 5-6 September.
The St James's Park event will be a village-fete-inspired showcase for the capital's gardening clubs to pass on advice and encourage visitors to give gardening a go. Held in conjunction with the Royal Parks, visitors will be offered tours of the park's allotments.
There will also be activities for children, live music, shire horses, bunting, planting demonstrations, advice surgeries, competitions and seed giveaways.
The day is free and runs from 11am to 3pm.
The weekend events will be organised by the country's 2,800 gardening clubs affiliated to the RHS.
RHS director general Inga Grimsey said: "We know that our gardening societies and clubs are the custodians of grassroots gardening. They all have fantastic knowledge, advice and tips on everything from protecting the environment through gardening, right down to how to grow giant marrows. But like all clubs they need the support of new members. By organising this day we hope more people will get bitten by the gardening bug and the knowledge these clubs hold will be discovered by new generations."
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