A couple in Kent have turned their hop farm into a lavender paradise – and have perfected the use of the herb in the kitchen, too.

Twelve years ago, William and Caroline Alexander, who own the 17th-century Castle Farm, decided to devote 55 of their 1,200 acres of mixed arable farm to lavender. It is now one of the largest lavender farms in the country, and one which oddly has a particular appeal for the Japanese, who obviously view the eight weeks when the lavender is in flower as an extension of cherry blossom viewing. 'One family took a taxi all the way here from Heathrow, and asked where they could leave their suitcases,' Caroline tells me.

The Alexanders now produce a wide range of culinary products, toiletries and herbal remedies, most of which are produced from lavender oil, their principal product. But what makes them unique are their culinary essences - one for hot food, and one for cold. Initially the couple wanted to expand their food range to include lavender ice cream and shortbread, 'but we realised we needed to have a culinary essence,' Caroline says, 'as we couldn't achieve consistency by using the flower heads alone.' Since the introduction of the essences in 2006, they have been championed by chefs throughout Britain, including Raymond Blanc and Gordon Ramsay. Over two weekends in July, 4,000 visitors descend on Castle Farm for the annual lavender festival. But in fact the flowering season begins in mid-June and ends in mid-July when the lavender is harvested and distilled. Each summer the three Alexander children, all in their twenties, return home to help.

For centuries Kent has been famed for its hops, the raw material for brewing beer. The Alexanders have been growing hops at Castle Farm since William's great-great-grandfather bought the land in the 1880s. But increasingly he found himself under competition from North American and Eastern European imports. By the late 1990s he, alongside other local producers, realised that his time was up. 'We needed an alternative intensive enterprise to hops on the farm,' William says, although he still produces hops on a limited basis to sell as cut flowers and to use in their farm's own herbal preparations.

The Alexanders teamed up with 12 other Kentish farmers to have their land analysed for suitable alternatives to hops, and were told that lavender, rosemary and German camomile were the most suitable. 'We knew that lavender was a good long-term investment, it wasn't just a fashion crop,' William says. They were also advised of an emerging market for 'traceable' oils. With lavender from India, China and South Africa, there is little hope of establishing what variety of lavender the oils have been produced from. The burgeoning market in essential oils and upmarket cosmetics created a new demand. 'Buyers wanted consistent year-on-year quality, which is something we can provide,' Caroline says.

In the Middle Ages lavender was recognised by apothecaries for its cure-all properties, and grown as a herb in gardens; by the 19th century there was small-scale production within reach of London's markets, but gradually disease, urbanisation and the development of cheaper, synthetic perfumes saw lavender production die out in the late 1800s. With no tradition of lavender farming in Britain to speak of, there was little expertise for the Alexanders to call on.

The majority of the original group of producers lost heart and turned to other crops. But the Alexanders persisted and in 1999 set up a cooperative with two other growers to share their experience and the costs of production. Their research involved regular trips to Sault in southern France to meet local producers in order to lavender from India, China and South Africa, there is little hope of establishing what variety of lavender the oils have been produced from. The burgeoning market in essential oils and upmarket cosmetics created a new demand. 'Buyers wanted consistent year-on-year quality, which is something we can provide,' Caroline says.

In the Middle Ages lavender was recognised by apothecaries for its cure-all properties, and grown as a herb in gardens; by the 19th century there was small-scale production within reach of London's markets, but gradually disease, gain the necessary knowledge. Most incredibly, their principal variety, Maillette, a French lavender with a particular gentle sweetness (it produces the highest-quality lavender oil), was originally grown from two cuttings the couple secreted in their hand luggage on a journey back from Provence. The other varieties they grow are the 'Folgate' lavender, and the hybrid lavandin Lavandula x intermedia 'Grosso', which accounts for 90 per cent of French production.

The huge machine that harvests the lavender two rows at a time was new last year. Caroline recalls how when its predecessor, a single-row harvester, broke down during the harvest one July, it was her job to get it fixed. 'It was a mercy dash by plane, down to Marseille and then a hire car, which I turned around in 24 hours. I was disappointed that security never questioned why I was carrying half a gearbox with me.'

After cutting, the lavender is taken to a custom- designed distillery on the farm, an ingenious system where steam is forced at high pressure through the lavender to extract the oil. The scent in the air as the lavender is distilled is intoxicating, and the Alexanders have put the relaxing quality of angustifolia to good use in their Sleepy Tea, a blend of lavender, camomile, rose petals and English hops. The x intermedia 'Grosso', which has a noticeably sharper scent, has traces of camphor, and is used as a room fragrance, in candles, as a mosquito repellent and in their Morning Booster tea, a blend of lavandin, rosemary, ginkgo, echinacea, lemongrass and white tea. A visit to the Castle Farm shop shows the extent to which lavender can be utilised - their lavender food lines include salt, chocolates, fudge and tea.

But most exciting for any cook are their small jars of dried lavender flowers, which can be used to make a delicately scented shortbread, or scattered over green salads and roast beef. Lavender is a herb that straddles the divide between sweet and savoury. But it is probably most familiar as one of the key ingredients in herbes de Provence (which blends thyme, fennel, savory, marjoram, rosemary and lavender), as well as in the beautiful sables or shortbread for which Provence is known. It is a flavour that may give you a sense of déjà vu - traces of its soft mellow tones are one of the secrets behind Coca-Cola, some cherryades and even blackcurrant cordial.

In a bid to create a product that would be a genuine reflection of the perfume, a few years ago the Alexanders approached a flavour chemist, Arthur Phillips, who runs Elixarome, a company that creates aromatherapy oils and culinary essences, to see if he could come up with a flavouring to cook with. The result is the two lavender essences, a 'cold' one that is water soluble and good for ice creams, champagne cocktails and salad dressings, and a 'hot' one that is fat-soluble and good for baking or roasting, that little bit stronger to allow for the loss of flavour at a high temperature. 'You can create a homemade essence by boiling lavender flavours with water and sugar, but it's not consistent,' Caroline says. Lavender's great talent is to soften sharp fruits such as gooseberries and rhubarb, lessening the need for sugar. And its scent works wonderfully with sharp citric flavours, such as lemon cheesecake or in a lemon sauce with chicken. As the Alexanders' passion for lavender gains pace, we may soon be overtaking Provence in discovering new ways to use its flavour in our kitchens.

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