The move, which stems from a £1.4m hole in Wakehurst's annual finances, is part of a drive to become self-sufficient. Jackson said the future for Wakehurst, owned by the trust, will include more festivals and events focused around the venue's botanic and site of special scientific interest status.
"People don't come to places like Kew and Wakehurst to primarily learn about conservation," he said. "What we need to do is put on festivals that are cultural and aesthetic and then get the ecological message across."
Wakehurst's problems derive from a 1965 contract with the trust that leased the grounds and later the house to Royal Botanic Gardens, Kew but stipulated that trust members could visit for free. They now form 80 per cent of visitors and only bring in income on shop and cafe spend. Jackson said the trust is unwilling to renegotiate this aspect of the lease.
After consultations and market research, both groups decided a parking charge was the most acceptable option for trust members rather than downgrading the horticulture, which Jackson said would be a "slippery slope".
There is an annual £1.4m deficit in running costs, which are £2.2m in total - paid for so far from Kew central funds. Jackson has introduced a cafe and shop at Wakehurst, but said the extra income has only covered rises in running costs.
Some visitors are opposed to the parking fees. Uckfield resident Ashley Leaney called the idea "absolute folly". He added: "My wife and I will not pay to park at Wakehurst Place. If parking charges are introduced we will not renew our National Trust membership. If the charge is made, members across the country will avoid Wakehurst Place."
Jackson said shop, cafe and visitor numbers will be down in years one and two - by about 40 per cent in year one alone. He also expects the annual 335,000 visitors to fall to 200,000.
He is relying on repeat National Trust visitors taking up an offer of £25 to park all year round. Around 70,000 people visit the site at least four times a year. He said by 2016-18, income could break even thanks to £1m a year from car parking.