Metroland meets the tropics: Kiwi Dave Bryson's horticultural homage to his native land

The Metropolitan Line was never part of the life I once lived in London. But I had one of the classic early posters issued by the railway, promoting the cosy domesticity of these outer suburbs: hollyhocks, delphiniums and a Shirley Temple-esque child running down a path to greet her father returning from the office (via the Metropolitan of course) to his castle.

The Metropolitan was the first underground railway in the world, already by 1868 joining Baker Street to Swiss Cottage, then pushing on fast to Rickmansworth, Chesham and Aylesbury, which it had reached by 1892. It was a smart move on the part of the railway to set up a property company and create the Metroland that became one of Betjeman's favourite themes.

For him, Chorleywood represented the essence of this particular world. I'd set the epicentre at Northwood Hills, where the Metropolitan Line's station, opened in 1933, served the commuters of a new suburb, rapidly developed during the Thirties by the Belton Estate Company. All the cultural markers are there: long straight roads of half-timbered houses, with bow windows and leaded lights; an occasional purple-leaved plum, still standing in a front garden (the purple-leaved plum Prunus cerasifera 'Pissardii' was the must-have tree of the Thirties). It was a baking-hot day when I wandered down Oakdale Avenue and Briarwood Drive, the air heavy with the smell of privet. Too heavy.

I'm not looking for countryside (there's plenty of that at home), but I'm certainly looking forward to some happy rubber-necking among the front gardens of Metroland. I'm disappointed. More than half of the front patches are now paved over. I think of those neat lawns, the forsythia and American currant now suffocated underf block and tarmac. The lack of green is stifling. I'm panting for plants.

Then I turn into Ferndown and, like an oasis, the front garden of number 54 shimmers provocatively in my sights. You can't miss it: monster cordylines with trunks as thick as telegraph posts; architectural tetrapanax with vast, stiff leaves obscuring the front door. And a huge, meaty agapanthus with leaves twice as wide as anything that grows in our garden and a bud just about to burst open on top of a three-foot stem.

In the drive, mostly filled with a green and yellow van, the owner of this miraculous agapanthus is unloading a lawnmower. He's Dave Bryson, a New Zealander who, 30 years ago, left his home in Christchurch with his life savings and wandered the world for five years ("You could live a long time then on $5,000") until, much to his surprise, he found himself settled, with a family, in England.

"I was a surfer, a beach guy. Having watched Coronation Street at home, England was the last place I thought I'd ever be." But here he is, working now as a landscaper, after a previous life as the original white-van man, delivering freight from the docks to addresses in the West End.

The cordylines (New Zealand natives) he'd grown from seed, he said. And the tetrapanax. But he didn't bother too much with the front, he said. I ought to come round the back. But not before he'd mowed the lawn. Quite honestly, he needn't have bothered. The lawn so obviously is not where his heart lies. It's just the jaggedy bit in the middle left over from the beds where he puts in all the things that really turn him on: palms, cycads, agaves, aloes, cacti, succulents and strange, tropical ferns. The lawn, which flooded badly in the torrential rain, is actually trying hard to join the bog behind it where the carnivorous snouts of pitcher plants rear up out of the undergrowth. Bryson points out how the local spiders have learnt to crouch in the tops of the pitchers, waiting for dinner.

Once round the corner of his house, you're in some part of the southern hemisphere, some damp, semi-tropical place of enormous leaves and tree ferns and curtains of creepers cascading off trees. It comes as a shock to hear a ghostly, disembodied voice reminding you not to leave your luggage unattended: the Metropolitan Line is just behind the back fence, which you can't see because it's presently a dumping ground for the fern house that Bryson hopes to build there one day.

At the moment, the ferns, beautifully settled in pots made from the fibrous trunks of their cousins, the tree ferns, sit on a platform raised up on old telegraph poles on the left-hand boundary of the garden. It's where the last of the evening sun comes through and Bryson thought he'd sit there of an evening, nursing a glass of NZ white and dreaming of waves in Hawaii. But he's not a sitting kind of guy and gradually the potted ferns took over.

Underneath is a zig-zag arrangement of beds, slightly raised inside lengths of railway sleeper. They are filled with more things that I can't spell than any borders I've ever seen. But not just filled. Carefully arranged so that a striped vriesea displays itself to maximum effect alongside the solid, goose-bumped trunk of a grass tree (Xanthorrhoea – see what I mean about the spellings?). Barrel cactus and superb aloes have fat juicy aeoniums and echeverias bulging beneath them. Tall eucalyptus screen off views on either side, the grey-green of their leaves morphing into the grey-green of Agave ovatifolia, perfect in its symmetry.

Displayed on a promontory where a zig meets a zag is the jewel of Bryson's eclectic collection, a palm that nobody knew about until the Nineties when it was introduced from Yunnan. For one day only, see Trachycarpus princeps, the biggest in captivity, tomorrow (11am-5pm), admission £3. For more info, call David Bryson on 020-8866 3792 or e-mail davidbryson@sky.com. The garden at 54 Ferndown, London HA6 1PH is just five minutes walk from Northwood Hills station.