The former BBC TV and radio host, who is also honorary president of Hampstead Garden Suburb Horticultural Society with his wife, said: "Gardening clubs are great for getting together, getting outdoors and exchanging gardening know-how. We’ve learnt so much from our own society."
This year’s event, held on the weekend of 4-5 September, will be an opportunity for around 100 RHS-affiliated gardening clubs and horticultural societies to engage with potential new members through a range of activities.
A recent RHS survey showed that around half of such groups were undergoing a growth in membership, with new members citing "social reasons" as their main incentive for joining. Nearly 60% of members are aged 60-plus.
For details of individual events, see www.rhs.org.uk/digtogetherday