Gardens of England and Wales Open for Charity lists 3,500 carefully tended properties whose owners allow horticultural tourists to come in and poke around on a couple of afternoons a year, with a viewing season that gets into its stride around now. From admission charges often as modest as pounds 1, with children half-price or free, the National Gardens Scheme last year raised pounds 1,830,000 for medical charities. Gardens of Scotland is a more slender volume. In Surrey alone there are almost twice as many properties on view this weekend as there are in the whole of Scotland; on the other hand, Sunday's attractions north of the border are mostly castles.
England too can offer many a stately home - Cliveden, Sissinghurst - and palace, in the case of Blenheim, which had its NGS openings last month. Yet the unstately homes are just as intriguing; they show that green fingers can produce results in urban areas where the odds seem stacked against even dandelions surviving. Just a trowel's throw away from my house, near London's South Circular, is a space measuring 75ft x 45ft, the garden of 125 Honor Oak Park; as you'll be able to see on 23 and 30 June, this offers "multifarious froth on two levels, the lower shady with small beds, the upper sunny with grass and pots".
Is the opportunity to hobnob with the nobs an added attraction? Of course not. However, should you wish for a glimpse of the Duke of Hamilton, you will need to know that he is at home from noon on 19 May at Lennoxlove, Haddington, East Lothian. Even without his Dukeness, the 14th-century house is a big draw. For an extra two quid, you can go on a conducted tour to see the death mask of Mary Queen of Scots.
This Sunday you could be chatting about caterpillars with the Earl of Chichester, who lives near Salisbury. Or is it the Earl of Salisbury who resides near Chichester (see Little Durnford Manor, Wiltshire, in the list of weekend openings, below)? Both English and Scottish "Yellow Books" have an above-average number of titles among the home-owners; some are professors, many are hons or sirs.
But on 30 June you can be treading on a lawn owned by both a lord and doctor - none other than those potentates of the potting shed, Jeffrey and Mary Archer, whose Old Vicarage, Grantchester, Cambridge boasts the old chestnut trees featured in the poetry of a former resident, Rupert Brooke.
Whether Jeffrey's novels are in the same literary league is a debate I'd urge you to avoid, should he be flogging them to unwary visitors, though you may care to peer through the windows in an attempt to spot that fax machine... you know, the one he did NOT see when Anglia TV faxed Mary Archer with the sensitive info about its shares.
Gardeners who take part in the scheme are organised folk, otherwise they would never have progressed beyond the overgrown shambles with which the rest of us end up. Some manage to co-ordinate their openings so that if the hollyhocks in one garden do not appeal, visitors can always try the neighbour's clematis.
Malvern Terrace, London N1 offers a spectacular example of horticultural togetherness. On 12 May, numbers 1-8, and 10 (what's wrong with number 9?) open all their "cottage-style gardens" for a combined entrance of pounds 1.50 (children free), and that includes musical accompaniment. Like many owners, they offer homemade teas - and a plant stall (if any visitors to any "Yellow Book" grounds try to snip illicit cuttings, they deserve to end up at the bottom of a compost heap).
Like Malvern Terrace, many of the properties are accessible to wheelchairs. The garden at 190 Goldcroft, Yeovil, Somerset (29-30 June) is not only ideal for the visually handicapped but was actually created by a man who is virtually blind. As well as building walls and a raised pool on railway sleepers, Eric Crate has arranged a route that rewards senses other than sight; by brushing past plants, the visitors hear the rustle of leaves and smell the newly released scents.
Another of the gardens opening for the first time this year is The White Cottage, Beech, near Alton, Hampshire. This is unusual, partly because it is open on Monday afternoons as well as Sunday (9-10 June, 14-15 July, 11-12 August) and partly because its owners have a collection of more than 50 carnivorous plants, souvenirs of a stay in Nigeria. Also new to horticultural tourists, The Elms, Ramsey Gardens, near Huntingdon is an old brick quarry, born again as a series of interconnecting ponds. And the site features a graphic demonstration of the ultimate in gardening tips: a row of Dutch Elms, saved from disease by the insertion of large copper nails into the base of their trunks, presumably on the same principle that copper bangles ward off arthritis in humans.
While all the resident gardeners will answer queries to the best of their abilities, you can expect an extra high standard of reply at Bryan's Ground, Stapleton, nr Presteigne, Hereford & Worcester (19 May, 21 June), the home of Hortus, the gardening journal. Watch out for "blood red Astrantias and black tulips with purple foliage placed near obelisks".
In some cases, my own question would not be about which fertilisers were used for the foxgloves but how the property acquired its name. With anything called the Old Rectory, of which there is an entire column in the index of the "Yellow Book", the answer is that an old rector used to live there. But Darkey Pang Too Gang? That is the name bestowed upon a lush three- quarter acre with pergola and bog garden near Shepton Mallet, Somerset (16 June). And if you ask the name of the property in Jarvis Brook, Crowborough, Sussex which opens for the NGS (12 May, 9, 23 June, 7, 21 July and 4, 18 August) you'll be told: Cobblers.