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.

To Kew on a perfect June day for a serious all-day session on, of all things, tree safety. The IDS organised the seminar with Tony Kirkham, the head of the arboretum, as a consequence of his horrific week in court last year when a branch fell off a cedar and killed a girl.

Accidents and Acts of God are old-fashioned concepts with little, if any, place in current law; the blame culture has to pin every misadventure on a cause, and the cause on an individual. The Royal Botanical Gardens owned the tree (a cedar of Lebanon); Tony Kirkham is responsible for all the 14,000 trees in the collection. If a tree is unsafe (the presumption if it sheds a branch) it should have been made safe. Under Health & Safety laws Tony might have had to go to jail.

His audience yesterday were people who either own or manage trees in arboreta or parks all over the country. I think they were shocked, all of them, at the risks they are running in letting anyone near their trees. Their duty of care extends to every tree and every branch, and the only way to satisfy a court is to show that you have inspected the tree in question, satisfied yourself that it is not about to break up, and kept records of your inspection. It is only the fact that Kew does have a long-term, fairly elaborate and fully documented inspection regime that saved Tony from clink.

True the family of the unfortunate girl were on the attack, hired a QC and an expert (who turned out to be not extremely so in court). We were full of questions. Does the duty to inspect apply to trees in ordinary gardens? (Yes). Does it apply to trees in woodlands or forests? (Yes). What about the notorious and mysterious phenomenon of ‘Summer Branch Drop’, when a major branch parts company with its tree without warning, for no perceptible cause? For some (or no) reason this happens most often in June, July or August. There is even a superstition that the time to stay away from trees is on July 22 and 23. Tree professionals prefer to let S.B.D stand for Sudden, rather than Summer, Branch Drop – not having a clue how it relates to a particular season.

We spent the afternoon on a practical tree-inspection tour of the arboretum, following Kew’s three-stage system: first walk (or even drive) by at 3 mph with your eyes skinned, looking for broken or split branches, splits in trunks, signs of weeping or surface fungi. This you should do as often as possible, within reason. The second stage is to come back and examine what you spotted. Carry a mallet to tap the trunk for hollow resonance and an iron rod to prod the base for soft wood. Take action as needed: cut unsafe branches straight away.

Stage three is for when you can’t tell, or decide, because the problem is hidden inside. This is when the expensive toys come out: an electronic device called a Picus Sonic Tomograph that reads the speed of sound-waves through the trunk to build up a picture of the interior. You hit a nail at intervals round the tree; the sound travels fast through sound wood, slowly through rotten wood and not at all through hollow cavities. The rule of thumb is that if one-third of the trunk is solid the tree can stand. Less than that means the chop.

Of course other factors come into it. A hazard (the possibility of something going wrong) is not the same as a risk (the chances of it doing damage). There is obviously more risk where more people congregate, by a path or a road, then in the middle of a wood. Your action can be proportional to the risk, so when a grand old specimen by a path begins to look a bit wonky Tony Kirkham’s first step is to move the path. More people walk on short grass than long, so he lets the grass grow or creates a wide circle of mulch around the trunk (which is also, of course, good for the tree). There is obviously a degree of proportionality in the precautions you must take – but the fact remains, the buck stops with you.

And you must contemplate the possibility of extreme bad luck: the Kew cedar branch not only brought down two others, but a huge chunk of wood bounced. The poor girl was six metres outside the radius of the tree.

It was a landmark case. Not long afterwards the National Trust was able to use the same defence of regular inspection and records. But it sent a shudder through the gathering. We all went home to brush up our logbooks.

Another six-day excursion, this time to the Gers, Armagnac country north-west of Toulouse. Four days with afternoon temperatures of 35c or 95F produced miraculous changes in the richly farmed landscape. Seedling crops appeared in immaculate emerald rows from the bare earth. Crops that were in that embryo stage one day shot to bushy bulk three days later. Grasses started to flower, tinting the fields, and the patchwork of the woods in half a dozen greens moved perceptibly towards the sombre uniformity of summer.

It is a landscape where each prominent hill has its bastide, ranging from a single tower to a small hill-town, ringed with woods. From its walls you look down into bowls of fertility. Wheat, sunflowers, corn, potatoes, tobacco, rape and even peanuts fill the valley slopes with varied colours. From our hosts’ house delicious glimpses between copses of oak or elm or pale walls of ancient stone change with the circling sun or the unpredictable moon. Their soundtrack changes, too: from the clamour of swallows to the hoot of hoopoes to the mesmeric solos of a nightingale.

Meanwhile in London a couple of warm days had brought the garden, when we got home, into its first phase of summer colour; quiet in our shady beds, campanulas and white foxgloves and the new tawny fronds of ferns, cheerful on the walls with pale clematis, roses Bantry Bay, Gloire de Dijon, Iceberg, Phyllis Bide and Alister Stella Gray, and raucous above, where our neighbours’ roses, unrestrained, wave fat blooms in red, white and pink above the foam of climbing hydrangeas.

Ambiguous robinia in Tokaj

A weekend in Hungary to see the Tokaji vineyards in their spring finery: hillside after hillside covered in files of the singular pale green of young vine-shoots. The shoots are three feet long, up to the top wire of the trellises, their flowerbuds visible, utterly vulnerable to a frost – unlikely in late May but still conceivable. And a horrible black hail-cloud sailed by this afternoon.

The village gardens and the forests on the hilltops are at their best: forests in their primitive state, a mixture of every imaginable species, unplanted, unthinned, seemingly impenetrable until you come to a stream winding down a shady valley, gardens brimming with pale flowers; irises and peonies the favourites. Roadsides are full of wild roses, pink campion, purple sage and blue vetch.

The forests have a problem, though: the invasion of robinia (or as we tend to call it) acacia. At our old home in the centre of France, in the Foret de Trançais, where the oak is supremely “prestigieux”, robinia crops up everywhere except deep in shady woods – and sometimes has a go even there. Every roadside is lined with it, suckering and seeding prodigiously. Its thorny progeny are good at self-defence. In May and June its masses of white blossom are popular with passers-by. Then its dreary little leaves dominate the rich mixture of textures and hues of the native trees.

How did it spread so far and so successfully? Presumably France had its equivalent to William Cobbett, who so enthused about the peerless value of this new import from America – named, by the way, after Jean Robin, director of the Paris Jardin des Plantes. Its timber makes the best fence- or vine-stakes, splitting easily and impervious to rot. There is even a fashion for using it for barrels, too, especially for sweet white wines. So farmers must have planted it, little thinking that soon it would be such a formidable weed.

What is odd in Hungary is that whole stretches if it have pink flowers: like tall lilac from a distance, and interspersed with the white of elder trees indisputably pretty. I consulted Bean online (so can you. Google ‘Bean’s Trees and Shrubs’ to get to the IDS website, where the whole of ‘Bean’ is available for consultation, free). Is there such a thing as a robinia species with pink flowers? No, is the answer. There is a nursery variety, R. x ambigua (a good name) decaisneana, produced in France nearly two hundred years ago. But how could this become a widespread wildling in Eastern Europe? I must do more digging.

Meanwhile in the country at large field after field, scattered among vineyard plots, are strange orchards of elder trees on short trunks, explosions of creamy-white blossom, in long straight rows. When you see a crop repeated country-wide at random the reason is usually a government subsidy. But what can Hungary do with so many elderberries?

A chunk of Chatsworth

A happy chance took us to the Flower Show on the first fine day of the week, Thursday, when Chelsea was looking at it’s sunny and cool, sparkling, rain-washed best. I feel a heavy responsibility as I ponder the annual Trad Award. (The rules are simple: it’s the garden I like best). This year, for once, I fully agreed with the RHS judges: the Chatsworth/Laurent Perrier/Dan Pearson garden was not just the best in the show, but the best ever in my Chelsea experience.

The feat of carrying a large chunk of Paxton’s over-the-top rockery down from Derbyshire was pretty awesome. We explored the real thing for the first time last summer; even by Victorian standards of ambition the perching and piling of such monstrous boulders on a steep hillside seems, shall we say, a trifle exhibitionist. Nor is the result, I fear, an aesthetic triumph. Far more satisfying and exciting are the natural rocky outcrops at Wakehurst Place.

Dan Pearson’s genius is to extract a subsection, as it were, to install it at Chelsea, and to present it as an exotic meadow garden of wild and not-so-wild flowers. We were told that Crocus, the contractors (who surely deserve their own gold medal) planted the seed mixture on mats which were then cut and fitted into their precisely planned places in the scheme, among the rocks, around the gently-flowering little stream, between the trees and lapping down to the tight-packed crowd of admirers.

Even the dead leaves scattered in the grass came from Chatsworth; romantic realism can hardly go further. The grass, besprinkled like a medieval tapestry with flowers, was thicker here, thinner there, scuffed by feet along a winding path, the gritty soil loose here, compacted there and constantly changing in a floral concerto, ranging from buttercups to peonies, hostas and ferns to eremurus, campion to wild strawberries, primulas, sweet rocket, day lilies, euphorbias, rare irises, geraniums, rodgerias….shaded here and there by field maples, azaleas that looked benignly neglected, enkianthus, a laburnum just showing yellow buds, a huge clipped box bush and a great fat willow pollard impossible to imagine packed up and on the road, A list of plants does nothing to express their happy intermingling. An example: a single Welsh poppy acting the weed, ‘a plant in the wrong place’ among pink primulas, just skews the scheme into complete conviction: this could surely never have been on a drawing board.

One other garden challenged for the Trad Award: the complete contrast of James Basson’s Occitane garden representing the scents of Provence, a little olive grove in a dell, watered by a shining runnel made of rough tufa blocks and splashing into two tufa tanks. In one corner stood a lavoir; a simple shed, also of grey tufa unadorned, playing the cool and shady part a grotto would play in a grander garden. It was a happy idea to dig the whole area to a lower level so the crowds peered down into it.

James Basson (we have worked together in Beaulieu-sur-Mer, on my son in law’s garden) knows when to stop. There is bare earth here, ready for more planting; you sense the humble gardener is just taking a break round the corner. There is enough decoration and detail in a scattering of flowers and the intricate shadows of the olive trees on a little table and chairs. Pastis would probably be the drink in such a tranquil unpretentious corner of Provence.

I admit I had never noticed the church opposite Waterloo Station before – nor its garden. St John the Evangelist is, appropriately enough, one of the four ‘Waterloo’ churches built with a million pound grant from parliament after the battle we are celebrating in June. It apparently looked out of date in the 1820s when Gothic was the new approved ecclesiastical style; people thought its splendid Grecian portico, however dignified, was old hat.

Its generous burial ground is now a model urban public garden, admirably planted, well maintained and with lots of green space for games and picnics. The very opposite, in fact, to the proposed Garden Bridge which was the reason for my visit. I was asked to speak at a public meeting against the project from the gardener’s point of view. The church was packed with objectors, invited by the newly-coined TCOS (or Thames Central Open Spaces). Most of the objections centred on the cost of building and running this odd hybrid, and whether ‘public’ money should be spent on it. The cycling lobby is furious that you can’t bike over it; the disabled that it won’t (or rather wouldn’t) be wheelchair-friendly, and everybody that it would effectively be another commercial space for holding events, closable at will, and not a proper public bridge at all.

I made the point that it is a crazy place to put a garden. Artist’s mock-ups show it as a sort of park with full-sized trees. What tree would grow properly in what is essentially a long thin planter exposed to every wind that blows? The essence of a garden is shelter, seclusion, and space to linger. The plans show the bridge would have none of these. At busy times it could be like the Chelsea Flower Show; necks craning to see any plants at all.

But the greatest objection of all, overriding all other considerations, is the casual way that Boris, his friend Joanna and their star designer, Thos Heatherwick, would override the history that has created London’s greatest spectacle; the grey tideway of the Thames hurrying, dawdling, rising and falling between its gritty beaches, its monumental banks and its serious, grownup bridges. They would stick their folly in the finest view of all with, as The Times wrote, ‘all the elegance of a Saudi prince’s gilded loo’ – and just as much relevance.

There is a judicial review of Boris’s unorthodox procedures scheduled for June. Money is needed to pay for it. Please visit the TCOS website and make a contribution.