Using water to soften soil baked hard by the Caribbean sun and then scratching away with plastic spoons, a handful of prisoners have reportedly produced sufficient earth to grow watermelon, peppers, garlic, cantaloupe and even a tiny lemon plant, no more than two inches high.

The revelation of the garden has now been seized on by campaigners, seeking to close the prison camp in Cuba, who have urged supporters around the world to send them seeds which they will in turn seek to send to the prisoners. They have termed their campaign "Seed of Hope".

The existence of the garden - apparently prohibited by the US military authorities - was revealed by the Boston-based lawyer Sabin Willett who was informed of it by one of his clients, Saddiq Ahmed Turkistani, held at Guantanamo Bay since 2002.

Mr Willett said that, last year, the US military deemed Mr Turkistani was no longer an "enemy combatant" but that he remained in legal limbo because no country was prepared to take him. Mr Willett said lawyers had regularly pressed the authorities of Joint Task Force Guantanamo [JTFGTMO] about establishing a garden but that they had refused.

Mr Willett told The Independent that he was explaining this to Mr Turkistani on a recent visit when he was told the prisoners already had a garden. " I could not believe it," he said. "I knew they had no tools. If you take in court papers you have to take the staples out. The look on his face as he told me how they had unscrewed the mop handles and used buckets of water [to build the garden] was something wonderful."

Mr Turkistani said he and other prisoners held in part of the prison known as Camp Iguana softened the ground with water overnight and then used the spoons to dig. Every day they managed to loosen more soil until they had enough for a bed for planting. "We have lots of time here," he said.

Gardening has long been associated with POW camps. At the Harperley POW Camp, in County Durham, built by the British for German and Italian prisoners during the Second World War, gardening was encouraged, along with educational classes and football.

Mr Willett said that, when he put the request to JTFGTMO, he was told gardening was not permitted. "These people have been put in such a hellish situation and yet, somehow, they have found a way to create life, literally," he said. "They have had to take the seeds from their meals and then scratch at the soil in order to get that going." Mr Willett, who first wrote about the garden in The Washington Post, said he had not personally seen the prisoners' garden but had been told of it by three different detainees.

Mr Turkistani's plight is especially pitiful. An ethnic Uighur who was living in Afghanistan, he had been jailed by the Taliban for three years and then freed by the Washington-backed Northern Alliance in late 2001 before being transferred to US custody. Last year, Mr Turkistani, who was born and raised in Saudi Arabia, was cleared for release from Guantanamo Bay. His lawyers say he is guilty of no crime and should never had been seized by the US. He was accused by the Taliban of being involved in a plot to kill Osama bin Laden - an allegation he denies.

But the future of Mr Turkistani and the eight other cleared prisoners - five Chinese Uighurs, a Russian, an Algerian and an Egyptian - who live in the less restrictive Camp Iguana, remains uncertain. He does not hold Saudi citizenship and the US does not want to send him to China because of the discrimination against Uighurs there.

The UK-based campaign group Reprieve has urged people to send seeds. They have established a PO Box, details of which can be found on the group's website www.reprieve.org.uk.

Reprieve's legal director, Clive Stafford Smith, said: "The massive might of the US military is intent on holding prisoners in an environment that is stripped of comfort, humanity, beauty and even law. Yet the prisoners held there have overcome this with a plastic spoon and a lemon seed. It is the beginning of the end of Guantanamo Bay."

Spurred by the fact that only a handful of detainees have been charged, there have been repeated calls for the closure of Guantanamo Bay, which was established for prisoners captured in the so-called "war on terror" . A UN Human Rights Commission report published in February called for its immediate closure.

JTFGTMO yesterday failed to respond to queries. Last year, a Pentagon spokesman said of Mr Turkistani's case: "The government is serious about finding a place for resettlement for the Uighurs and will continue diplomatic efforts to accomplish that goal."

The Pentagon said this week that around 140 of the 500 prisoners held at Guantanamo had been reclassified and were no longer considered enemy combatants.