Private view: Take the rare opportunity to sneak a peek over a few fences of Britain's best gardens

This time last year, I persuaded my friend Jo to spend her Sunday afternoon looking at four gardens on Kew Green, a short walk from where she lives. "So they're just opening their gardens to the public for one day?" she wondered, as if she could hardly imagine anything more bizarre. But the Kew Green gardens in south-west London are part of the National Gardens Scheme (also known as the Yellow Book scheme after its distinctive directory), where thousands of Britain's best gardens, hand-picked by a team of knowledgeable local experts, open for charity over the course of the summer. And yes, in many cases, you have just a day to seize the moment.

I knew I'd made a convert when, after a quick look around, Jo reached into her handbag and started rifling around for a piece of paper and a pen. "What's this one?" she asked, admiring the purple balls of alliums growing through huge silvery artichoke leaves. "And these?" she asked about drifts of aquilegia that had self-seeded through meadowy grass. And, most importantly, "Could I grow that?"

I imagine that when a garden is accepted into the National Gardens Scheme, the first question to be asked is, "When will you open?" So many owners must plump for May, knowing their garden will look fresh and beautiful. The drifts of purple and blue in the Kew Green gardens certainly made a convincing case that the right date had been picked for their big day.

But I often find myself wishing I could come back later in the year to see how the garden develops. In gardens opening this weekend, with roses and clematis not yet in flower, there will be tempting hints of a glorious June to follow. And there are certain Yellow Book gardens which aim for the late August heat, with a much more tropical feel. There are visiting dates to suit anyone, ranging right into autumn, with the first snowdrop openings beginning again in February.

If you want to find out about gardens in the scheme, what you need is the Yellow Book (£.8.99), sold in supermarkets and on National Trust gift counters as well as in local bookshops. If you are a paperless household, you can head to www.ngs.org.uk and use its "gardenfinder" feature.

Even without a horticulturally minded friend to tour a garden, you are in safe hands. The owners are usually hovering, delighted to give advice and remember plant names, sometimes pressing you with tea and cake too (for an extra £2 or so). In fact, I have known owners to take the cake-making so seriously that it overshadows the need for last-minute weeding. So get yourself a copy of the Yellow Book, and head off on an adventure where you never know quite what you'll find. Just leave enough room for a second piece of cake.

Kew Green gardens are open today, 2pm-6pm

Open season: Three plots to peruse

Brize Norton gardens, Oxfordshire

A whole village opens its gates, so you can see a range of gardens looking their best. The jewels are Painswick House, with roaming chickens, and the lovely Lingermans, with its masses of spring bulbs. Admire the flower festival in the church, too. 14 June, 1pm-6 pm

28 Multon Road, London SW18

A gorgeous town garden with modern planting, bananas and phormiums, but also unusual cannas and day lilies. 30 August, 2pm-6pm

Meon Orchard, Hampshire

A stunning garden, well worth the trek. Drifts of hardy ginger and eucalyptus trees take you miles away from the English countryside, though views cut through remind you of the green grass of home. 31 May, 26 July, 6 September, 2pm-6pm