As the Chelsea Flower Show prepares to open its doors on Tuesday, three-time medallist DIARMUID GAVIN picks his favourite gardens in the UK and Ireland

The Eden Project and The Lost Gardens of Heligan, Cornwall
Talented conservationist Tim Smit was responsible for breathing new life into the once abandoned Lost Gardens of Heligan (01726 845100/www.heligan.com) near St Austell in Cornwall and also for creating a green haven in a nearby disused quarry, the two huge Mediterranean and Rainforest biomes which form part of The Eden Project (01726 811911/ www.edenproject.com).

There's loads to see at Heligan including the lush subtropical jungle with its exotic trees and plants; the Northern Gardens, which produce loads of fruits, vegetables and herbs; and Horsemoor Hide, which is the perfect spot to view local wildlife.

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While the more traditional Lost Gardens feel as if they are from another century, the Eden Project is much more modern. It's a garden of the people and raises a whole host of concerns about our planet and how we use our resources. It is hugely inspiring.

Where to stay: The Scarlet (01637 861800/www.scarlethotel.co.uk), just outside Newquay, offers doubles from £180 per night (two sharing), B&B.

Derek Jarman's garden, Romney Marsh, Kent
Film-maker Derek Jarman created the most marvellous gardens at Prospect Cottage, in the shadow of Dungeness power station, before he died in 1994.

He would walk the shingle beach and pick up plastic, metal, driftwood, fishing tackle and anything else washed up on the shore.

He also used hardy plants that would stubbornly cling to the ground to create this unusual garden. You can still admire his creation, just look out for the cottage with the sculptural driftwood as you head along Dungeness Road.

Where to stay: The George (01797 222114/www.thegeorgeinrye.com), in nearby Rye, offers doubles from £135 per night (two sharing), B&B.

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Mount Stewart Garden, Co Down, Northern Ireland
Nearly 100 years ago Lady Londonderry created this beautiful national treasure in Newtownards.

Mount Stewart Garden (028 4278 8387/www.nationaltrust.org.uk) is now run by The National Trust.

Realising the area had a unique microclimate, Lady Londonderry built large formal flower beds that now have a distinct Mediterranean feel. There is humour, too, as stone statues are dotted around reputed to be named after famous visitors.

Where to stay: Ten Square (028 9024 1001/www.tensquare.co.uk) in Belfast offers doubles from £89 per night (two sharing), B&B.

easyJet (0871 244 2366/www.easyjet.com) offers return flights from Luton, Gatwick and Stansted to Belfast from £42.

The Dillon Garden, Dublin, Ireland
Some 30 years ago flamboyant Scot Helen Dillon moved to a Georgian house in Dublin's Ranelagh area where she has created Dillon Garden (dialling from the UK: 00 353 1 497 1308/ www.dillongarden.com). It's in Sandford Road, a street where I once lived.

Originally, she built a very formal lawn but then she shocked the gardening world by taking out the lawn and replacing it with an Islamic pond. It's a huge, striking water tank that reflects the sky and really takes the breath away.

Where to stay: The Merrion Hotel (353 1 603 0600/www.merrionhotel.com) offers doubles from £170 (two sharing), room only.

Ryanair (0871 246 0000/www.ryanair.com) offers return flights from Luton, Gatwick and Stansted to Dublin from £64.

The Garden of Cosmic Speculation, Dumfriesshire, Scotland
Architectural historian Charles Jencks designed this garden, inspired by the creation of the universe, in the grounds of his home Portrack House (www.charlesjencks.com) near Holywood.

Huge mounds of turf rise into the sky to produce bridges, landforms, sculptures and terraces that tell the story of black holes, life and creation.

You can arrange a visit with Scotland's Gardens Scheme (0131 226 3714/www.gardensofscotland.org).

Where to stay: Trigony House Hotel (01848 331211/www.countryhousehotelscotland.com), in nearby Closeburn, offers doubles from £100 per night (two sharing), B&B.

To read Diarmuid's full travel guide, see www.simonseeks.com