I have never actually washed my garden before. It’s the ground you usually water, not the leaves. But the builders next door send over such a dust-storm that after weeks without rain every plant was grey with grime. I’m sure it was stopping them growing; flowers were fewer and fewer – and sadly dingy.

So I got out the hose and sprayed the whole place; drenched it all over – an hour’s work the other night. How effective my artificial rain was I shall never know; it’s been stair-rodding down all day.

Later: how does steady rain have a totally different effect from watering? You can fill pots to the brim regularly, but the day after a downpour they look quite different, more buoyant, ready to perform. Is it the atmosphere, the pressure, the humidity?

The visitors book proves it: I was last here fifty years ago – and nothing has changed. The broad white verandah still looks out over orange trees to the steep terraces of vines going down to the river. The house, verandahed all round, sleeps like a planter’s bungalow on any tropical station, lawns shaded by thick trees (in this case limes), screens closed against mosquitoes, the rooms complete capsules of times long past. Deep beige armchairs, faded prints, dusty books, the polished dining table, have not changed since the 1960s. Probably not since the 1920s, when the Gilbey family bought the estate, 150 acres of vines and the stone barns where Croft’s port has been trodden time out of mind.

The upper reaches of the Douro, a hundred miles from the sea through range after range of steep hills, are dry, hot and fertile. When we arrived the other day there had been four days over 40º, the conditions that make great vintage port. It’s a long time since we slept as past generations have, bare under a sheet hoping for a draught from windows open on both sides of the house, resenting the mosquito screens blocking the free passage of air. The thermometer drops to 30º at dawn: I get up to open all the doors to let the cool air in, and doze off just as the sun shoots its first shrivelling rays into the house.

The early morning is when the vines can get to work, photosynthesize and swell their grapes. In this exceptional summer veraison , when the grapes turn colour from green to red, is already under way. By mid-morning, vines that stood trim and gleaming have started to droop; their stomata closed; evaporation exceeds the power of their roots to find water in the parched soil. They look hangdog until evening, metabolizing nothing, losing time in the journey to ripeness. Fig trees show signs of the same stress, their big leaves limp. Olives, on the other hand, with their small grey leaves, seem immune to the heat. The agapanthus are unbothered, too, baking under the dry stone walls. And orange trees gleam on regardless.

I’m afraid I react like the vines, with the advantage that I can hide in the shade and dip my feet in the fountain. Our hosts’ labrador, on the other hand, has found a niche in a flower bed and lies between hydrangeas and agapanthus with a lime in his mouth for refreshment.

Quercus exceptional, a Berkshire native

It’s a problem photographing a tree like this one. But then there aren’t many. The trick is to ask a patient friend to stand by it and walk away until you can fit the whole tree in your lens. Communicate by shouting.

This oak is in a garden near Newbury in Berkshire. No one can see it without asking questions. How old is it? How wide? How high? But above all how? There are taller oaks, and girthier ones, but are there any so complete in their domes, with branches stretching so far in an uninterrupted circle?

Part of the answer may lie in the way it was evidently planted, it must be four or five hundred years ago, on a mound of earth. The sapling was planted on the summit of a mound some five feet high and perhaps thirty feet round. Why? The soil below is heavy clay; perhaps the gardener thought it would get away better on a hill of something easier for its roots to penetrate. There is another magnificent tree three hundred yards away on a similar mound. Yet curiously the woods around are full of strikingly tall straight oaks, big beeches, soaring Scots pines and lime trees of immense size. So why the mounds?

The rest of the garden, I should say, is in keeping. Many plants seem larger than life, and it is quite a collection, centred on a water garden round a large stone-edged water tank, ingeniously fed from a smaller and slightly higher tank in its centre so the water is always gently moving. The owner, Rosamund Brown, is a painter of memorable abstract landscapes; her sense of colour makes the planting sing – a tune that changes abruptly when you pass the door to the kitchen garden into a Mondrian world of primary colours and daring contrasts. Another smaller enclosure is planted entirely with cactus and sedums; the ultimate low-maintenance plants, but a startling display, and I guess a unique one in a garden.

Broad York-stone paths link the elements: formal to woodland to glasshouses and pools. And it is as though the fertile earth below resents their weight. Self-sewn volunteers push up between the slabs and are carefully edited, so that here verbascums, there agapanthus or daisies or campanulas embroider the grey stone.

While I’ve been mugging up on fruit history I’ve come across a curious strawberry fact. Our big juicy ones superseded the little European native wood (French fraises des bois) or alpine strawberries (some debate here: are they the same or different?) when the American Fragaria virginiana met and married the Chilean F. chiloensis, introduced (the curious fact) by a chap called Frézier (fraisier: geddit?) – or in Scots, come to that, Fraser. Our strawberry’s botanical name is F.x ananassa, ananas being French for pineapple. One of our best and tastiest varieties is ‘Cambridge Late Pine’.

Note to supermarkets: please label our strawberries (and indeed all our fruit) with the name of the variety as well as where it’s grown. And don’t harvest strawberries by cutting off their stalks and leaving just the green ring of bracts. You need the stalk to pull out the central plug when you put the strawberry, crunchy with sugar, in your mouth.

Who said, incidentally, ‘the raspberry is the thinking man’s strawberry’? Discuss.

Louis XVIII is a monarch you don’t hear much about, France’s last and perhaps fattest. He lived for a while at Hartwell House, was too overweight to walk, and had a predegustator who doubled as librarian of his 11,000 books. This chap’s job was, among other things, to pass fruit as acceptable for his majesty.

My authority, Edward Bunyard (d. 1939, pomologist and epicure) relates how everything stopped when Christophe, the gardener, knocked at the library door with a new variety of peach. Petit-Radel, the predegustator, waited while Christophe, with his ivory knife, cut the fruit in four. The first quarter he judged for its juice; the second for its flesh, the third for its aroma and the last for its harmony.

Bunyard, in his Anatomy of Dessert, came down in favour of the nectarine over the peach, on grounds of both its flavour and its smooth skin, though with some reservations about texture: less buttery, more fibrous than the peach. He cites fourteen varieties, and twenty of peaches (La Quintinie, Louis XIV’s gardener at Versailles, listed thirty-three). Since then breeders have selected and bred scores more. Rivers of Sawbridgeworth, for example, offered a whole aviary of peaches with bird-names: Kestrel, Goshawk, Sea Eagle, Peregrine… Apples and pears have been bred in hundreds. Where are they all?

The RHS has given an AGM to a mere five (the nectarines are ‘Lord Napier’ and ‘Early Rivers’, the peaches ‘Duke of York’, ‘Peregrine’ and ‘Rochester’). Look for the name of the variety in a supermarket: the country of origin is usually all we’re told. The truth is we don’t have librarians who predegust or gardeners knocking at their doors. The supermarket buyer predegusts, or certainly should, but is more concerned with price and shelf-life. If a pear needs an alarm clock to announce its fifteen minutes of perfection you won’t find it at Waitrose.

What you do find these days is flat peaches – a happy sport of the ancient fruit that suits both shops and customer (and even waiters: they don’t roll off the plate). Flat peaches grow on the branch face to face, like headphones – another of Chinese nature’s endless repertory of brainwaves. Their flesh is as sweet and juicy as any peach (so juicy there is apparently one variety you can drink with a straw; Louis XVIII would be in raptures). They pack perfectly, tighter than round fruit, to please the carrier. There is even, so I read, a nectarine or fuzz-free kind, though not yet at Waitrose in Kensington. Its name is Mésembrine. My father used to call peach-fuzz ‘goobra feathers’. He wasn’t in favour: definitely a nectarine man. What advance can we hope for next, since we’re doing so well?

The hardest peach to find in a shop is the pêche des vignes, the profusely juicy red-fleshed kind that ripens as late as the grapes in the vineyards where you usually find it planted. It gives the vigneron, they say, an early warning of mildew in the air. You need a bath after eating them, but if by some miracle a flat and fuzz-free sport appeared I’d certainly have a word with Waitrose.

A warm weekend’s visit to the battlefields of the Ypres salient, one hundred years to the day after my father was wounded there by a round from a German Maxim machine-gun. He carried the bullet in his wallet for the rest of his life in an envelope marked “German bullet that wounded G.F.J. in June 1915 at Ypres, taken out at Guy’s Hospital by Sir W. Arbuthnot Lane”

He was secretly rather proud that he was operated on by this famous surgeon (the model, it was said, for Sir Cutler Walpole in the Doctor’s Dilemma), incredibly soon after being wounded. Trains were shuttling the wounded from the front to Calais and London. ‘I woke up’, he wrote to his mother, ‘in a London Hospital’. He was lucky. But six months later he was back with his battery (he was in the artillery) in the same spot.

The cemeteries tell the story of some of the worst battles. The bodies were buried near where they died, at the beginning of the war in nearby churchyards, soon in plots appropriated as cemeteries. One of the biggest, with 12,000 graves, is beside the principal ‘dressing station’ by the railway.

The cemeteries are gardened by The Commonwealth War Graves Commission, to a standard the Royal Parks would be proud of. There are many miles of straight edges and immaculate hedges with white headstones in parade order. Some have pavilions or cloisters whose walls carry the endless lists of the dead, listed by regiment. Tens of thousands are anonymous, but those that were identified carry the name, rank and regiment of the soldier, and most of them his age, very often between 19 and 25. In June scarlet roses and bright purple lavender form our tricolour with the white Hopton Wood stone that was generally used. Their trees form an arboretum, interestingly chosen and perfectly kept. There is much to learn in these battlefields – even about gardening.

My brother-in-law, Simon Relph, has made a beautiful and ingenious little garden behind the 14th century farmhouse by the famous tithe barn at Bradford on Avon. Its glowing stone gable peeps through the walnut tree at the end. Simon has contrived lawn, pond, terrace and a rich choice of plants and left himself room for an immaculate vegetable garden, framed last weekend by roses at their peak. “Rambling Rector” spreads its froth of flowers for fifteen yards along the old stone wall.

But they’re moving house. A lucky successor will inherit five years’ work. We were taken to see his next intended project, a modern house with three times the garden space – and I confess to a twinge of envy. If he can encapsulate so much in the confines of the old farmhouse yard what fun he’ll have with this almost-virgin territory.

We discussed the trees. They are the first and most crucial decision in any new garden. How do you weigh the fact of an established but dull tree against the chance of choosing something better? Of course you plan for both. A few are so revolting that the chop can’t come soon enough. A worn-out Prunus amanogawa (the pink cherry that apes a Lombardy poplar) is instant firewood. A droopy old Lawson cypress might be spared (but mainly on the grounds that it isn’t a Leyland). A dingy purple plum gets its quietus (not to mention that most villainous of shrubs, the yellow-leaved choisia). What to do with a misshapen neglected ash? A clever surgeon could improve it. But there’s a centenarian beech to one side and a thriving walnut in the middle. And space for fruit trees, magnolias, dogwoods,…

My instinct (not that it’s my garden) is to consider the light and shade first. Decide where you’ll want lunch on a hot sunny day. Make your shady spots as appealing as you can. White furniture under a handsome tree draws people’s feet like a magnet.

Next comes the division of space; the apportioning of rooms. Will it be explicit, as in clipped hedges, as implied by the massing of plants? Or, of course, both? I can’t wait to see it take shape.

The Piet Oudolf garden at Bruton belongs firmly in the present, Oudolf was given a sloping field beside the new Hauser & Wirth art gallery (whose restaurant, a sort of tidied-up Petersham Nurseries in Skye Gingell’s day, vaut le détour). Oudolf, as everyone knows, plants abstracts with sinuous blocks of “prairie” plants. There are no impediments to your eyes wandering over a vast field – nor any plan, it seems to me, in the paths wandering round the beds. You can romanticize about the sense of space, the breadth of the sky, the movement of the wind in the (many) grasses. The two garden essentials of shelter and seclusion are totally absent. Do they (as I half suspect) represent, to a right-on modern world, infected with socialism, the privileges of privacy – or indeed the privacy of privilege?

Here’s a simple rule for creating a memorable garden: choose a south-sloping hill with a gushing spring at the top. Then tease the water down, across, fast and slow: play with it; let it lie in pools and splash down steps, shallow steps and steep ones, singing different tunes.

This is the formula at Shute House in Dorset, refined to concert-pitch by Sir Geoffrey Jellicoe over many years for Ann and Michael Tree. It put me in mind of Ninfa, that supremely hydraulic garden south of Rome, where a crystal river races through the ruins of a medieval city. Shute is the English Pastoral version, smaller, quieter, shady rather than sun-baked, but equally haunted by Naiads, the nymphs of springs and streams and pools.

Did I hear that Romans discovered the spring at Shute Hill? If they were ever here they could hardly have missed it, and knowing their taste for water they would surely have made the most of it. It rises, these days, in a circular pond perhaps twenty feet across, half-lost (and half-found) in thick curtains of laurel and rhododendrons.

So much water wells up from the crystal depths that it leaps down the overflow to ripple the surfaces of a pièce d’eau perhaps a hundred yards long, a dog-leg shape so designed as to seem two different ponds. One is sinuous, a little Stourhead banked with lawns and rhododendrons and navigated by black swans, the other a calm canal contained in high beech hedges, leading to a deft sketch of a Roman theatre.

The divided waters continue on their separate ways. From Stourhead they tumble into another informal pond and continue as a shady stream crisscrossed with meandering woodland paths. From the canal they emerge under tight control in a garden of stepped terraces, splashing and gurgling between parterres full of every plant that loves moisture and warmth.

That game over another begins: a racing runnel down a grassy glade; leaping with such brio into three hexagonal ponds that the pressure feeds little fountains to ruffle their mirrors. Each leap is a little organ of pipes tuned in a different key; the air is full of watery notes, from murmur to tinkle, through bubble and splash.

That long-disused word ‘felicities’ needs reviving to describe the various incidents en route. There are arches leading to more enclosures, more parterres of bold planting, little bridges and towering trees. The classical stone house lies to one side, its terrace surveying a long view to distant downs and the next destination of the playful water: more ponds in the fields to reflect a cloud-banked sky.