For most gardeners, repotting an old houseplant needs no more than a trowel and a plastic planter.

For the horticulturists who look after the oldest pot plant in the world, however, it a job for a gantry hoist, two pallet trucks, a hand-made mahogany box and nine hard-hatted workmen.

All were assembled at the Royal Botanic Gardens in Kew yesterday as gardeners prepared to repot “the king of the Palm House”, a 234-year-old Eastern Cape giant cycad that has a good claim to be the oldest potted plant in the world.

The cycad was just a seed when it was brought to Kew from South Africa in the year before the American Declaration of Independence, but it has grown implacably at about 2.5cm a year.

It weighs almost a tonne and the trunk, 4.5m long, juts out almost horizontally and teeters precariously over the tropical ferns beneath.

Wesley Shaw, Keeper of the Palm House, began the day feeling rather nervous. This is not a plant used to sudden movements.

“The worry we had was that any shock might snap the trunk,” he said. “It is heavy, but we don’t want to take any risks with one of Kew’s star plants.”

The move had been months in planning and had to be made, Mr Shaw said, because “the compost was horrible and the old pot was falling apart”. The pot was last repaired 20 years ago but no one is sure how old it is.

Days were spent rigging up a gantry and pulley system above the cycad. The old pot was torn away and a sling was lashed around the root ball.

Then, yesterday morning, the lift began. Five gardeners braced themselves beneath the trunk, like a horticultural version of the raising of the flag at Iwo Jima.

Chocks were kicked away and the cycad hung in midair while gardeners manoeuvred its handsome new mahogany home beneath it (tropical hardwoods are apparently the most durable materials in a humid environment such as the Palm House). Very gingerly, the great plant was lowered into the pot and tamped down with compost.

Mr Shaw breathed a sigh of relief. “We’ve lifted stuff before, but nothing this size,” he said. “Hopefully it’s going to stay where it is for the next 234 years.”

That is not an implausible wish, for cycads live for about 500 years. They are an ancient family that has changed little since the days of the dinosaurs, and that predates flowering plants. The repotting is perhaps the most exciting thing to have happened to the Kew specimen since it last produced a cone. That was in 1819.

By then, the plant was already long established in the gardens. The cycad was brought to England by Francis Masson, the first collector sent out by Kew. He sailed for South Africa with Captain Cook and brought back hundred of exotic specimens. That was in 1775, when Jane Austen was born and George III was not yet mad.

The cycad has not gone far since. “It’s quite an easy plant to look after,” Mr Shaw said. “They’re tough plants that can grow in very poor soil.”

He hopes that the new compost and larger box will this year double the usual growth rate of the plant.

The cycad found its permanent home when the Palm House was built in 1848, although it was moved for a few years in the 1980s while the glasshouse was refurbished.

David Cooke was among the Kew gardeners who moved it then and was back to lend a hand yesterday. He judged that the move went off “exceptionally smoothly”, and seemed more concerned about the next task on the horizon.

“In the Temperate House we’ve got the largest indoor plant in the world, a 165-year-old Chilean wine palm that’s 18m high and weighs 80-90 tonnes,” he said.

“We want to do restoration work but how on earth are we going to move that?”

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