Mr Loder's great grandfather moved to Leonardslee in 1889
A Grade I listed garden in West Sussex which has been in the same family since the 1850s has been put up for sale.
Leonardslee Gardens, at Lower Beeding near Horsham, is being sold complete with a deer and wallaby park which attracts up to 50,000 visitors a year.
Robin Loder's great grandfather married into the family which then owned Leonardslee and moved there in 1889.
He has two sons and two daughters, but he said the family felt it was now time to move on and sell the property.
""It is not that they are not interested in the gardens, but they all have families of their own and other interests," he said.
But he said his son, Christopher, would continue to run a propagating nursery on the estate.
Mr Loder, 64, who lives in East Sussex, said he had mixed feelings about the sale, but had greatly enjoyed expanding the garden into the surrounding woodland over the last 25 years.
Wallabies roam free in the gardens as "mowing machines"
"I have had the fun, the challenge and the priviledge of building it up and it is looking fantastic now," he said.
"The visitor numbers are perfect for the size of the garden - it never feels overrun."
The 225 acres of gardens include a deer and wallaby park.
Mr Loder said the 40 or so wallabies were used as "mowing machines" on grassy areas of the gardens, particularly the banks by the lakes.
"They roam free, rather like rabbits, and being from Tasmania are perfectly acclimatised to our weather," he said.
Leonardslee's Beyond the Dolls House exhibition is being sold in a separate lot from the gardens and other estate buildings.
The display has a scale model of a country estate as it might be found in a typical Victorian Market Town.
The gardens, plus a house and outbuildings, are on the market with Savills with a guide price of £5m.