Harvest time is here again on Germany’s 1.2 million allotments: potatoes have to be hoisted out of the soil and the last of the peas must be plucked.

In the shed, next to the trowel and gloves, there will almost certainly be a well-thumbed copy of the gardeners’ bible written by Alwin Seifert, the country’s organic guru.

Now it emerges that at least some of Seifert’s useful tips in his bestselling book Gärtnern, Ackern-ohne Gift, (Gardening, Working the Soil without Poison) may have been gleaned from his observation of the experimental gardens set up on the grounds around Dachau concentration camp.

Tended by half-starved slave labourers, at least 400 of whom were killed, drowned in the carp pond or trampled into the mud of the latrine trenches, the Dachau gardens were established at the behest of Heinrich Himmler, Hitler’s security chief, and stretched to 211 blossoming hectares.

Seifert, who after the war became a founder of the Green movement, was one of the top landscape gardeners of the Nazi era. He even had the title Reichslandschaftsanwalt — advocate of the Reich’s Landscape. It was Seifert who managed to persuade the Nazi autobahn planners to make the motorway curve, following the natural contours of the German countryside. The well-connected gardener was also opposed to artificial fertilisers poisoning German soil and went to Dachau, apparently oblivious to the emaciated prisoners, to see what could be done in the gardens and arable fields of the Fatherland.

“The question has to be how much of the information that flowed into his book derived from the research being done in Dachau,” says the Munich-based cultural historian Daniella Seidl, who has been digging in the Bavarian and federal archives. “He was a regular visitor, maintained a correspondence with the head gardener Franz Lippert, and even arranged for a couple from the camp to work in his own household.” Some of the ideas being tried out in the Dachau gardens were certainly adopted by Seifert for use in his own garden in the Tyrol.

The Dachau complex was supposed to solve some riddles, such as why potatoes had become so vulnerable to pests and early decay, and to build a more or less scientific basis for an alternative “biological-dynamic lifestyle”.

That meant growing herbs for use as medicine, extracting vitamins, but also Germanising food.

Fermented blackberry and raspberry leaves were used to create German tea, reducing dependency on imports, and work was done on making a German pepper.

Gladioli were grown in great quantities to milk them for their vitamin C. The leaves were dried and pulverised in the camp garden complex and then mixed with a mixture of spices, beef fat and cooking salt to make a food supplement for SS troopers.

The gardeners also planted fields of primroses in a first attempt to extract an oil for use as medication. Evening primrose oil is now frequently used in complementary medicine.

“Seifert was probably most interested in Dachau’s use of compost techniques,” says Ms Seidl, who has just published her findings in a scholarly book, Between Heaven and Hell.

The Dachau gardeners set up herds of cows over 750 hectares (1,850 acres), tended by up to 800 inmates, whose task was to gather the dung for testing in the camp gardens.

The effect of dung on the soil was measured; a special compost was devised to speed the growth of healing herbs. This ran in parallel with experiments using worms to improve differently fertilised soil.

Seifert’s book goes into great detail about composting, and how it helps in poorly productive orchards. He writes with the authority of someone who has studied a large-scale project.

Unsurprisingly Seifert does not mention Dachau in the book, but he does give an appreciative nod to his old protector in the Nazi machine, Fritz Todt, the armaments minister and lord over millions of forced labourers.

Seifert joined the Nazi party in 1937. He became a professor at Munich technical university, head of the nature preservation league (a forerunner organisation to the Greens) and before his death in 1972, influenced a whole generation of organic garden planners throughout Germany and Europe.

The passion for organic gardening gripped Germany and has never let go. Whether it will survive the horrific images that emerge from Ms Seidl’s research, the imprisoned priests who were strapped to ploughs, the inmates killed for taking a bite of raw rhubarb, the overseer who received a cash bonus for shooting his 100th Jew among the gladioli, is another matter.

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