"I don' t have a greenhouse," she explains, "and I'm designing a garden for the Chelsea show. These are some of the flowers I'm going to put in it - heliotrope and nicotiana."
It will be her seventh Chelsea garden. At a time when there are still reverberations from last year's scandal over exhibitors buying their show plants from outside suppliers, it is salutary to know that at least some of the immaculate blooms in the designer gardens will have began life humbly, by the kitchen sink of a cosy GIoucestershire home, warned by the Aga.
"I haven't yet discovered where other designers get their plants for Chelsea," she continues artlessly. "Roses the size of cabbages and all that. Mine are ordinary garden plants that I've dug up and put in the back of the car to get them there."
This same direct, hands-on approach is evident in Jane's new book, Gardening Made Easy. While the title is a slight misnomer (if gardening were too easy it would scarcely be worth doing) she is concerned to address the basic practical problems faced by gardeners, especially new ones. Unlike so many glossy books, hers is the art of the possible rather than the scarcely attainable.
All the same, does the world really need it? Walk into a book shop and you will see the gardening shelves groaning with the weight of instruction manuals of all kinds. Why another one? Jane explains: "I've written pretty picture books about roses and ivies and my friends said: `How lovely, but why don't you write a book about how to garden? That's what we really need'."
Her main career is as a garden designer. A few years ago she was working on the garden of a publishing executive, who told her: "What I and others could do with is a whole course that will teach us about gardening from zero to being able to enjoy it."
Other books, of course, make similar claims, but what distinguishes Jane's is its down-to-earth quality. For example, it is unusual for gardening manuals to discuss the critical but sensitive question of relations with neighbours on matters such as overhanging trees. ("Ask them round for a drink - making a neighbour's life a misery is a game that two can play.")
In the same common-sense vein, it is the only such book I know that includes a picture of a clothes-drying carousel. Where to put a clothes line is a real problem for many in planning their gardens, seldom addressed by the glossier writers on design.
"I may be talking myself out of a job," says Jane, "but I think people are much too worried about design of their garden. Garden design is often about a wonderful bit of paving, a marble bust and a yucca and I don't think that's what most people want. If they do, they're never going to enjoy gardening; they just enjoy looking at the yucca. What's important is growing plants, and my book is more about that than any other aspect."
Jane, who is 56, became a garden designer and writer in mid-life. Her first career was in art galleries. Having stopped work to look after her children, she wanted to start again when they both began school full-time. She decided to try garden design in the mid-Seventies, a rarer specialisation than today.
"There weren't schools of garden design then," she recalls. "You could either go to an agricultural college or do what was called landscape architecture, which sounded marvellous."
She enrolled in a four-year diploma course in landscape architecture at Gloucestershire College of Art in Cheltenham. "It wasn't a particularly good way to learn because they were actually very snooty about gardens. They spent their time designing pedestrian precincts and parks that would be totally vandal-proof. They taught us very little about plants, except the six best ones to deter vandals - they're all varieties of berberis."
However, while she was on the course two friends asked her to design their gardens and after she won her diploma the business slowly developed. It is for the most part a seasonal occupation, so in winter she began writing books.
Her own two-and-a-half-acre hillside garden, with marvellous views west to the Severn and, on clear days, to the Welsh hills, is based on her unpretentious design principles. No yucca, no statuary; although she does plan to put in a pond. "I'm quite laissez-faire," she says, as we squelch over the lawn in our green gumboots. "For instance, I like celandine very much and I don't treat it as a weed. I like cow parsley too: I've got a cow parsley walk."
She clearly follows her own top 10 tips (see panel). Many of the beds are already covered with a thick layer of mulch, part horse manure and part spent mushroom compost. Her plants are arranged in group , and there are plenty of trees.
"A lot of my tips are based on my experience here," she says. "I've tried to boil down the mass of information you gather over the years into something fairly accessible. I hope people can begin at Chapter One and end up being competent and confident gardeners. But although it's practical, I hope that it's inspirational, too. And it's concise; bulky books like the Royal Horticultural Society's encyclopedias can be daunting."
Not that this is pocket-sized: it has 286 quarto pages with charming instructional diagrams by Ian Sideway and informative pictures. One of these shows the clothes carousel, with the all important low-down on where to place it:
"Out of sight of your windows, the garden sitting area and, if you are a good neighbour, next door's as well. Combine the useful with the beautiful by underplanting a carousel with aromatic herbs which release their scent when trodden on."
A delightful inspiration, which I suspect will never find its way into the RHS Encyclopaedia.
! Jane Fearnley-Whittingstall's `Gardening Made Easy' is published on Thursday by Weidenfeld and Nicolson at £19.99.Reuse content