Landscapes of the soul: What are the most important landscape designs of the last century? It's a question that garden expert Katie Campbell attempts to answer in her new book. She explains her controversial choices to Emma Townshend

'I've become fascinated with war memorials,' Katie Campbell says, with great passion. If this is not exactly what you'd expect from a newly published gardening writer, it's certainly a clue to the type of person she is - eclectic, enthusiastic and very engaged. Campbell's interest in gardens and landscapes began when she did an MA in garden history at Bristol University, taught by the formidable Timothy Mowl. His controversial books on the 18th-century garden are rapidly changing how we look at great landscapes such as Chiswick and Stowe, and she now teaches alongside him.

'I complained to Tim,' she says, 'that I'd finished the course with no sense of the modern world. He said, 'OK, well put a course together.' So I did.

'I'm certainly not a very good gardener,' she continues, with scrupulous honesty. 'I'm most interested in how politics and philosophy have been expressed in landscapes.' However her approach is far from being drily academic. In fact, reading her book, Icons of Twentieth Century Landscape Design, is more like taking a really good tour, with a knowledgable guide who can share those little gossipy facts that bring the whole thing to life. For example, Ludwig Mies added 'van der Rohe' to his name to make himself sound more aristocratic, Isamu Noguchi started off making ballet costumes for Martha Graham, and Charles Jencks' massively ambitious Garden of Cosmic Speculation is actually on land belonging to his in-laws.

The 29 chapters in Campbell's book each tackle one of the most significant landscapes of the century, and her choices range from the unmissable - such as Frank Lloyd Wright's 'Fallingwater', with surrounding cascades and forest - to the rather more unexpected, like Eggborough Power Station, Yorkshire, landscaped with Buddhist clarity by Brenda Colvin, a scheme which deserves to be much better appreciated in her own country.

And she has fun along the way, speculating about why Le Corbusier had such an aversion to the earth (because of tuberculosis and trench warfare, in her opinion) and pointing out the only garden I've ever known to be subject to terrorist bomb attack (the Kennedy Memorial in Runnymede).

I ask her which one from the book is her favourite. 'Oh my God, I couldn't possibly say.' She thinks some more. 'But the one that moves me most is the Barragan. It's so incredibly serene,' she says of Las Arboledas, the Mexican designer Luis Barragan's 1959 masterpiece.

There's sociological detail to Campbell's writing: the Woodland Cemetery in Sweden, which contains an odd mixture of pagan natural spirituality, and completely new burial practices, has persuaded over 300,000 people to be interred there; Fletcher Steele's very first Modernist garden in America, with a black pool, under the influence of Freud, was intended to encourage visitors to contemplate their subconscious; and Roberto Burle Marx's rebellious, post-colonial use of the native plants of Brazil, took place at a time when wealthy South American patrons still expected European species only.

Finally, of course, there are those war memorials. What's the fascination? Campbell is clear: 'In the 20th century, people became aware of the horrors of war, so war memorials can't be triumphant any more. There's been an attempt by designers to evolve a completely new iconography for these landscapes, but it turns out that absolutely everybody has an opinion of what they ought to look like. So it's really complicated to try something new.'

Campbell highlights the case of the Washington DC Vietnam Veterans Memorial, designed by Maya Lin. Lin was a 21-year old Asian-American student when she won an international competition for her idea, which garnered both huge attacks and praise for its V-shaped gully, cut like a scar into the turf. 'She was told it should have been white, not black; that it should have gone up, not down; that it suggested shame, that it looked like a tomb. And then they were forced to add a sculpture of three servicemen and the American flag, to make it more like everybody's idea of what a memorial should look like. Yet it's so powerful - that simple device of names carved in stone, set in landscape - it's so poignant.'

The book as a whole makes you want to go and see some of these amazing landscapes, but maybe that's a project for next summer. In the meantime, I've been sitting on the sofa reading up on some of the ones I've already seen. I love Fondation Maeght, in the south of France, but it makes more sense to me now I've heard what Campbell says about the classical groves of its 'Labyrinth Garden', designed by Miro.

So who does Campbell tip as icon-makers of the 21st century? She likes Tom Stuart-Smith, who cleaned up at Chelsea this year. 'He combines architecture and horticulture so well, so that you have these clean lines, very modern, very abstract, with interesting plants.' So it's possible that Stuart-Smith's prairie garden at Trentham will be the early 21st-century landmark that many are predicting. On the other hand, maybe the most influential designed landscapes of the future will be somewhere we haven't even thought to look yet. Seattle's Gas Works Park reminds us that if you look hard enough, you can find a garden almost everywhere. s

If you do one thing... turn your bulbs

Over the next few weeks, houses are going to fill up with hyacinths, paperwhite narcissi, and the craning green stems of amaryllis, busting out of their pots. All bulbs grow towards the light, and indoors, at any time of year, they will quickly distort themselves in search of sunshine. To keep the flowers aiming straight upwards, you need to confuse the light-receptive cells at the top of their stems.

So, while making your cup of tea in the morning, turn all your indoor bulbs 90 degrees, and repeat the process daily (always turn clockwise, or you'll confuse yourself). Your perfectly behaved plants will wow your seasonal visitors.

Katie Campbell's 'Icons of Twentieth Century Landscape Design' is published by Frances Lincoln, priced £30