One incredibly productive farmer in Wales grows produce worth £25,000 a year – and says you can copy him in your backyard

Probably the most productive piece of agricultural land in Britain lies in the foothills of the Black Mountains in Wales. Here, on a modest 1½ acres, Dr Paul Benham and a handful of students and volunteers produce around £25,000 worth of organic fruit and veg each year. And the best bit is: you could replicate it in your backyard.

The variety and abundance here are staggering: five kinds of potato, half a dozen of salad, seven mustards. Herbs, from mint, marjoram and oregano to soapwort, sorrel, heartsease and hyssop. Chards, onions, garlic, spinach. Beets, beans, courgettes, carrots, peas, leeks, cabbages. More than 100 varieties of apple, pear, plum and nut.

Almost all Primrose Farm's produce is sold within five miles, mainly to restaurants and at Hay-on-Wye's weekly market, on a stall groaning with 30 varieties of spectacularly tasty produce. And bar 1,500 miles a year in a battered Volvo for deliveries, and a couple of gallons of diesel for a 60-year-old tractor used, at most, once a year, Benham does it all pretty much without fossil fuel.

He calls this high biodiversity, low-carbon polyculture – working with nature, not trying to control it. It's a resilient system that he argues can survive peak oil, even climate change. By contrast modern, energy-intensive, heavily subsidised monoculture – single crops grown in huge fields using copious chemicals and heavy machinery – looks unstable, and increasingly unsustainable. "This shows what's possible," he says. "A food system in harmony with the environment."

How does he do it? Benham's been developing his low-impact vision for 25 years at Primrose. It starts in a greenhouse, where seeds sprout in long-dead but still well-insulated chest freezers, each warmed with a low-energy lightbulb, before young plants are moved outside.

There's the all-important compost heap and two worm compost bins, and beyond, the farm's four main growing areas, rotated between potatoes, peas and beans, brassicas and salads, and roots and onions. Rotating the crops helps to help control pests and improve soil structure and fertility: each works the soil differently. In winter, Benham plants "green manure" (vegetation that covers bare soil fast, smothering weeds and enriching the soil), and lays black plastic sheets over raised beds to lock in nutrients. It's about interfering with the soil as little as possible.

Growing beneath the farm's fruit trees are fruit bushes, but also what Benham calls "smelly herbs": mints, lemon balm, tansy. The carrot root fly, he points out, can smell a carrot from 200 metres and these put them off the scent. (Similarly, a bog-garden of 70 wild plants and herbs attracts predator insects such as hover-flies and ladybirds that eat harmful aphids. A squadron of ducks are efficient slug-hunters.)

Further over, the farm's forest garden is designed to mimic natural woodland. Facing south, at ground level, are ground-cover crops such as wild strawberries. Behind may be slightly taller rhubarb, or globe artichoke, then low shrubs and bushes such as tayberries and blackcurrants. Further back still are dwarf apple and plum trees, and finally large fruit and nut trees, with shade-tolerating crops beneath, such as a carpet of wild garlic.

There's nothing to stop anyone doing this at home, says Benham. It's a question of designing carefully. Rotate your crops, feed them well, remove infected parts fast, offer no single target, confuse pests with strong-smelling plants and attract pest-eating predators with others such as fennel, chervil, asters and calendula.

And what of the eating? Obviously, food produced this way and eaten soon after picking has lost none of its qualities, and is super-good for you. Preserve enzymes and nutrients by not cooking it to death: eat raw; or cook on a low heat.

Lunch chez Benham is a festival of extraordinary flavours. Grated carrot and beetroot. Steamed Swiss chard and ground elder. Sprouted lentils. Rocket pesto. Hard-boiled duck eggs. Vegetable pâté with carrots and sunflower seeds. A hummus of raw sprouted chickpeas. Quince cheese. And a salad of dandelion, sorrel, sweet cicely, jack-by-the-hedge, clover, borage, nasturtiums, chickweed, red and green lettuce and three types of mustard. All followed by fresh berries. It worked for me, and it certainly works for the planet.

• Primrose Farm runs gardening and cooking courses: primroseearthcentre.co.uk