A Gulf in class: No county can touch Cornwall for the quality of its gardens in spring

It's all thanks to the warm sea air of the Gulf Stream, says Emma Townshend.

Gardens in Cornwall are big business: local business people in Falmouth have been campaigning for years to remove some rare seabed corals called "maerl" and drain a deep channel for gigantic cruise ships to approach this pretty town. When asked recently why anyone should actually want to get off the boats and spend money, the first tourist attraction they named was the Eden Project, closely followed by the Lost Gardens of Heligan.

Evidently, gardens in Cornwall are also delectable. Especially now it's finally decided to be spring. And nowhere does the season arrive with more gusto than in this seaside county, where magnolias and camellias have been doing all sorts of springy things for weeks now. There's something about Cornish gardens at this time of year, mainly powered by warm Gulf Stream sea air and lots of rain, where long branches hung with lichens give the valley-sides a rainforest feel.

You can see for yourself: Katherine Lambert is a gardening writer who lives near Truro, and her new book, Gardens of Cornwall (Frances Lincoln, £16.99),is crammed with 24 of the county's very best. The gardens of Anthony, Cotehele and Mount Edgcumbe kick us off. Super-romantic in feel, old-stone statuary and rambling roses add a twist to the magnolia-powered mix.

Other stars of the Cornish canon follow, such as Trelissick and Glendurgan (both National Trust, incidentally – this is one county where membership comes into its money-saving own). Trebah is one of my favourites, with sweeping beds,all equipped with perfect views of the Helford Estuary. And though Lambert allots eight pages to images of the Abbey Gardens on Tresco, I could happily look at 80 pages, so glorious is the mix of giant agapanthus and utterly foreign palms, all growing outdoors.

Lambert also includes some wilder cards: I've mentioned Tremenheere before, the imaginative creation of a local doctor who has planted rare palms on a hillside site above Penzance while also installing a James Turrell skyscape. And Barbara Hepworth's tiny garden in St Ives packs a mighty punch for its size – another garden with art at its heart that will send you home convinced you justhave to get some ratty geraniums.

So Lambert provides a great starting guide to the county's horticultural splendour. Yet stray a little off her version of the beaten track and there are even more good gardens to see. On a Sunday afternoon drive, posters flutter in the breeze marking gardens signed up to the Yellow Book scheme, tempting you down windy lanes to find extraordinary plots created by amateurs that are rarely open to the public. Godolphin Hill, open in Helston on 17 June and 1 July, for example, is the eco-garden belonging to a moth expert, who will show visitors his collection of beautiful lepidoptera.

At Bonython Manor, on the Lizard, Mrs Nathan and her team are making an extremely pretty garden with some wonderful touches, including a sweet orchard of local Cornish varieties where you can help yourself to tea and home-made cake, and a South African garden on a grand scale. I would also beg you to visit Potager, a garden-cum-café near Constantine outside Falmouth, in the ruins of an abandoned nursery (potagergarden.org). The sense of peace in a lazy hammock there is unbeatable.

So in conclusion: don't wait to arrive by cruise ship. Save the maerl! Come this year, by road, train or shallow-draught ship, and enjoy the finest spring fling that Gulf Stream gardens have to offer.

Spring gardens beyond Cornwall

Achamore

Wild gnarled trees and rare subtropical plants co-exist in a garden of quiet beauty on this tiny white-sand island east of Islay, negotiable by bicycle or foot. Entrance fee payable in honesty box, gigha.org.uk/gardens

Arduaine

A coastal garden on the Scottish mainland south of Oban crammed with rhododendrons, this is in full colourful blast by May. £6 adults, free to National Trust members, nts.org.uk/Property/Arduaine-Garden

Bodnant

Thought not quite by the Welsh coast, Bodnant still benefits from mild Gulf Stream breezes that allow a spectacular range of plants to be grown. £8.95 adult, NT and RHS members free, bodnantgarden.co.uk