Now and then I can’t resist quoting my correspondent in Japan. We have a mutual interest in special trees, and the weeping Katsura (Cercidiphyllum japonicum ‘Pendulum’) comes high on the list.

‘I have something very big and beautiful to show you,’ she writes. ‘I went to see the great weeping Katsura of Ryugenji’s Temple, in Iwate prefecture …a rusted sign erected in 1992 says it is 22 metres high … There was a breeze but unlike the slouched whip-like sweeps of a weeping willow it stood straight and just swayed slightly, like the ladies of Downton Abbey (although these trees are always male). The original tree, a Katsura mutant, is thought to have been found in the mountains and planted around 1574 when the temple was built.

There is evidence that it was felled in 1824, at 30 metres, to use a timber to renovate the temple. The present tree in from a basal shoot, thus about 193 years old.’ ‘All weeping Katsura might be related to this tree, standing behind a Zen Buddhist temple guarding a graveyard, with mostly rice paddies round it.’

But she ends on a note much nearer to home: the dreaded cydalima. ‘How to get rid of box caterpillars? Everyone seems to be crying for help here too’.

We have just been three days by the sea where the pine forest of the Landes meets the Atlantic on a beach a hundred miles long, dazzling sunshine slowly giving way to a misty sea fret and the relief of a faint breeze.

The Landes, or rather their forest, is a feat of man versus the environment. One million hectares of shifting sand and swampy waste were tamed during the 19^th century. It was a desert known only to the shepherds who crossed it on stilts. The first experiment in stabilizing the sands were made in the 18^th century, planting marram grass along the shore. Even now when you walk where nothing grows the fine white sand shifts and squeaks under your feet.

But the grass fixed the sand enough to plant pines, the local pin maritime, Pinus pinaster, a rugged two-needled tree with copious resin (collecting it for turpentine became the local industry). In due course they were followed by holm– and cork-oak, by arbutus, phillyrea, sea buckthorn, gorse and broom, willows and of course brambles. All contributed to the sterile dunes in stability and fertility. Their humus turned sand to soil.

Some of the dunes along the coast are still shifting, and so steep that you slide one pace backward for each two that you climb. There is an unexpected smell of curry in the air; curry plant is one of the pioneer sand-fixers. Then comes ‘la lette’, a shallow valley protected from the sea wind where pines, gorse, brambles and willows have a firmer hold. Then the forest, low at first, grows taller as you go inland and humus accumulates. The regular array of pines lets in enough light for what becomes quite a lush understorey. In places the arbutus, shining bright green, is the dominant plant, above acres of ferns.

It is hard to believe that only ten years ago, in 2007, 320,000 of the one million hectares were devastated in a gale. It was a regional catastrophe. There was no means or manpower to tackle the chaos of fallen and broken trees. The price of timber fell with them. We expected to see devastation still – and there are places where land has been newly cleared and cultivated; the sand has become soil enough to raise crops. But the vast expanse of forest, one the greatest feats anywhere of land reclaimed, still stretches to each horizon.

If anyone deserves the title of the plantsman’s plantsman it is Maurice Foster. We visited him at White House Farm in the green depths of Kent last month, after an interval of ten years. He hasn’t changed: still the rather impish, beaming figure with an unparalleled flow of botanical fact and anecdote to keep you happy all day. Maurice can recall every moment in the finding, naming, provenance and propagation of every plant in his collection of – I can’t remember how many thousands of taxa. His passion goes far beyond trees; he will be as eloquent on a rose, a grass or a lichen – well, maybe not quite as eloquent on a lichen..
The garden of White House Farm encompasses some four acres, a stretch of woodland a further three, and the arboretum beyond it seven. On Monday mornings, Maurice told us, two helpers get a briefing for the week; the heavy work to be done. The rest he does himself; a dizzying prospect as you look around you.

In ten years the arboretum has grown from a field of sticks to a leafy heaven of prodigious variety. Certain recurring genera amount to comprehensive collections; hornbeams in a variety no one would have thought possible; tilia, quercus, magnolia the same, berberis and philadelphus…. But a list of genera can sound like a dull plantation, and this is a magic wood of surprises and questions – to which Maurice has the answers.

Ten years is nothing in the life of a garden, or a gardener. At Saling Hall I was still planting more trees after forty years – closer and closer together. When I started I put them far too far apart, before I discovered that the thing trees (not perhaps all trees) like best is each other’s company. Every perambulation raised the question of priorities: does the beauty of that tree take precedence over the rarity of its neighbour? One or the other has to go. There were occasional duels, but I tended to let the happier tree win. The context, though, was different. I was trying to paint a landscape; in a landscape it is the spaces, more than the details, that count.

In the end an arboretum is a wood of different trees. In a good arboretum they are congruous; themes emerge, comparisons are close enough to be useful. White House Farm has all the beauties of a wood, but one where your eyes are constantly drawn to details of design you never expected to see.

Christopher Woodward has a taste for the grandest gardens; fair enough, they were usually the ones with the longest history. He has just led his coterie, supporters of the Garden History Museum, to what is in some ways the grandest garden in England. The fourth Literary Festival was held in perfect weather (another of Christopher’s trademarks) at Boughton House in Northants.

In modern garden history Boughton is best known for the remarkable horti-couple who lived there: Sir David Scott and his wife Valerie Finnis. He was a nephew of one Duke of Buccleugh and great-uncle (I believe) of another. He gardened there with love and style and industry until he was 99. His was the ‘wild’ garden; Valerie’s the alpines.

Meanwhile the 10^th duke (Duke Richard to his staff) has taken a new look at the more than impressive landscape. His commission of Kim Wilkie to design a contemporary take on the mighty earth-and-water works of the past is already famous. Matching the noble mount (the corollary to a noble pond) Wilkie dug a hole of corresponding size. Its name is Orpheus (who you remember visited the underworld to retrieve Eurydice). So the square pond at the bottom is the entrance (and in Orpheus’ unusual case exit) to/from Hades. The Orpheus depression (hole sounds too banal) has perfect acoustics. We sait on the grassy bank in early evening sunshine to hear I Fagiolini sing madrigals. Fa la la indeed!

If anything even more impressive than the glittering great plans d’eau are the avenues. The first duke planted limes in tens of thousands. The planting still goes on. With some of them three hundred years old, maintained (by topping, if necessary) at a height of 130 feet and astonishingly uniform, they are the ultimate garden accessory. Something like 30 miles of them.

But we were there to hear writers, a score of them, enlarging on their books. They ranged from Roy Strong to Alan Hollingshurst (who spoke on Assignations in the Garden. Maud was not the only who was wooed), from Anna Pavord to Michael Heseltine, Roy Lancaster and the Bannermans.

The strength of the symposium lay in its philosophical and poetic undercurrents. It was about the Why, not the How, of gardening, and it bore prolific fruit.

Oh, the blessed IT. I bought a new iMac to speed Trad along only to find it crawled slower than its predecessor (or should that be predewordprocessor?) The jolly little beachball – if you have an iMac you’ll know what I mean – turns and turns whenever I hit a key. I know it must be my fault, but it’s not Apple’s style to rush to the rescue. Except to sell me another of their devices. Hence Trad’s unaccustomed reticence recently.

Next step; a website on more modern lines, now under construction. Meanwhile a cheering photo of the judges at this year’s Chelsea Flower Show.

The depredations of the boxtree caterpillar, Cydalima perspectalis, have reached such a pitch in Kensington that Rassells Nursery has stopped sellling box plants for hedges. Instead they are offering a miniature holly, Ilex cornuta ‘Luxus Globe’,

Its leaves are smaller and darker than box. Its paler new growth at this time of year is quite pretty, but no one can pretend it will ever be a substitute for the mainstay of garden design for, literally, thousands of years. The Romans relied on it. Pliny the Younger cut it into extravagant figures at his villa by the sea. Populations of box trees are often evidence that Romans colonized a district. Where we lived in the Auvergne the outlines of a Roman town were still just visible, but the valley below was thick with ancient box trees. You didn’t find them anywhere else near there.

We all know its qualities as the trim and malleable friend of gardeners in the European tradition. Not everyone likes the evocative small of a box parterre on a dewy morning in summer, but the thought of a unique tradition chewed to oblivion to feed a nondescript little moth is hard to stomach.

We are defending our little hedges with whatever treatments are allowed. The caterpillars last year arrived in August ; in this strange spring they became obvious in chewed leaves and tiny webs in late March. The tiny caterpillars are hard to find but munch alarmingly fast. Even with daily inspection some survive – and turning your back to go away for a week is seriously ill-advised.

Ash trees, even elms, can be replaced with other trees, however we may miss their familiar silhouettes. Box, alas, has no real substitute. At Wisley there is a bed planted with possible replacements, trmmed as low hedges ; none, I fear, really cuts the mustard. Perhaps the best is Teucrium x lucidrys, or by its medieval-sounding name of hedge germander. The Prince of Wales evidently thinks so ; he has replaced box with it at Highgrove. Its chief drawback is its spikes of pink flowers, but I’m told hard trimming avoids them. Meanwhile, pray for a predator keen on cydalimas.