We don’t expect to spend much time on the broad sandy beaches of Snowdonia in August. Nor did we. But days of solid rain had done magic for the streams that chatter and gurgle through our woods. There are springs where I’ve never seen them before; the expensively-surfaced tracks are water-courses, their stones washed loose, and some of our stream-side paths have become stream-beds. But the new roof on our old mine building (we’ve upgraded its name from ‘the hovel’ to ‘Myrtle Mansions’) keeps us dry, and its new skylight lets in daylight we never had before.

There is a whole complex of ruined mine buildings where our goldmine used to be – or rather would have been if they had ever found gold. This was in the 1840’s and 50’s when gold fever seems to have broken out round the world: California, Australia, Canada, Colorado, New Zealand, and even Wales. (South Africa and the Klondike came later, in the 1880s). For a short while the Mawdach Estuary was a baby Ballarat.

Our mine includes the remains of the grinding shed, where the power to grind the ore was provided by a 30 foot overshot waterwheel, a couple of other buildings now reduced to their grey stone gables, and what we take to be the canteen and the manager’s office. The canteen has a huge hearth and the manager’s office a little one to keep his back warm as he watches his workers (some of them seven years old) through a panoramic (by Welsh standards) window.

But the best part is the mine itself, a horizontal ‘drive’ hacked and blasted a hundred yards into the hillside – at which point they realised that copper was the best they were going to get. The mouth of the mine is our grotto, a jagged hole in the hill, dark grey stone adorned with ferns, with a slow brown stream flowing out into the woods.

When we bought the property I was worried that someone might be tempted to explore, wander in and fall in the darkness, so I installed a gate of vertical iron bars. Years later I had a letter from the Welsh Bat Authority in Cardiff, telling me a colony of bats hibernated in the dripping blackness. Was I aware, it asked, that lesser horseshoe bats prefer horizontal bars? I still wonder who asked them.

To Kew to see the new Broad Walk Borders, all 640 yards of them, in their midsummer glory. Eighteen months after their inauguration they are splendidly established, and on a sunny weekend thronged with admirers. There was a long queue at the Victoria Gate waiting to get in, but then there is more than ever to see and do.

The balancing act between botanical garden and public attraction is not easy, but Kew is managing it well. There are a few visitors who complain that the museum building facing the Palm House over the pond is now a restaurant, but I’m sure there are more who are pleased to have a grown-up restaurant as an alternative to the predictable cafes.

The Broad Walk Borders are a wonderful tour de force, interspersing the cream of modern cultivars of the best herbaceous plants with things you won’t see outside Kew’s collections. I spent the best part of an hour admiring each side and its ingenious themes of plant families and reproductive systems. To solve the near-impossible puzzle of labelling in herbaceous borders there are plant keys at intervals, stylised coloured diagrams of each section that make it easy to identify the bold blocks and sweeps of different colours, sizes and habits.

Meanwhile the Temperate House is beginning to emerge from the covers that have hidden its years of restoration as possibly the greatest plant palace on earth. Next summer we shall see its full glory, too.

It was the shock of my gardening life. A phone call from my sister, just back from a week away. ‘Come and see my box.’ The caterpillar had come, and in a mere week had destroyed the entire framework of her garden. Her box hedges are bare, brown, leafless. The only colour is hundreds of green caterpillars crawling and munching and leaving their tiny brown droppings.

Not since Dutch Elm disease killed all our elms in the 1970’s have we seen such devastation of such an essential and universal plant.

My sister lives in a terrace house near Ravenscourt Park. Her garden, leading out from her kitchen, is the centre of her life. Her tomatoes, figs and grapes and apples could supply the family. But the structure of the garden, the chunky parallel hedges culminating in balls of box, is dead, an eyesore to be cleared away – no mean task. And then what?

The RHS website recommends Bugclear as a spray to kill the caterpillars: I’ve used it and it has no effect. Local advice here is that pyrethrum can be effective. You can buy it (until it runs out) under the brand name Py. It is too late, here, for pheromone traps, but I’m following up a new biological insecticide called Topbuxus XenTari that apparently poisons the caterpillars as they feed.

As replacements, substitutes for the box, there are plenty of ideas being mooted. Ilex crenata, teucrium, euonymus all field candidates. Even (and why not for a chunky hedge?) yew.  For my sister’s garden (and mine, when the dread moment comes) I’m contemplating myrtle. I’m not sure how it will react to a strict clipping regime; will it sprout new leaves as willingly as box? And where do I look for dozens of tiny myrtles? But myrtle, like box, has an aura, an ancient garden history, a presence that the other stand-ins can’t claim.

The first question you ask (or rather, I ask) when I see a place called Battlefield  is ‘What battle?’. It’s in Normandy, near Rouen, so my first guess is something in the Hundred Years War; a Crécy or an Agincourt. Not so, I discover. It was an inter-Viking affair, before Normandy became Normandy. Eric Longsword v Robert the Dane. A momentous scrap, surely, for the site to be remembered 1200 years later. Longsword won.

What is momentous today is the château on the site, and certainly its gardens. You thought (or I did) that Versailles, Vaux le Vicomte and that sort of horticultural bling was over centuries ago. Not here: we’re in kilometres of 8-metre hedge and hectares of gravel territory. This is a new garden (no; parc is the word). It stretches regally away from the immense facade of the chateau. (You could parade a regiment in its cour d’honneur, and I heard 10,000 horses mentioned as its 17^th century complement.) But there was scarcely a trace left of the original when work started on this.

Question two (after the battlefield one ) is who on earth can – or wants – to do a Sun King today? The answer is Jacques Garcia, the decorator-extraordinaire of Paris and its gratin today. The château’s apartments are as sumptuous as they must have been in 1660. His orchid-house, fern-house, and another vast glass salle simply for New Zealand tree ferns are on a national-botanic scale. Allée follows allée, and parterre follows parterre, enlivened with pools and pagodas, sphinxes of clipped yew, a Roman amphitheatre, vineyards, pergolas of heroic size, flower gardens and pavilions. The Indian one faces a hundred-yard canal punctuated by fountains, palms, daturas and flaring torches. They lead to monumental waterworks: fountains and cascades and scores of gilded spouting frogs – and finally to a massive canal that stretches far into the distance. In true classical style every part has symbolic meaning; the gods of Olympus are in charge – under the baton, that is, of Garcia and his gardener, Patrick Pottier. A million cubic metres of earth are a mere wheelbarrow to this Le Nôtre of our time.

I said last month that Boughton House was grand – and so it is. I will have to find another word for the French way of doing it. Grandiose, perhaps?

It was 1971 when I decided that agapanthus were worth the risk. Could we grow such midsummer beauty, elegance, and above all blueness, in Essex? The word at the time was that Headbourne Hybrids was the only reliably hardy strain. I chose a stretch of bed with no shade, laced the soil with gravel and protected the plants from wet for the first winter with slates perched on bricks. It worked. They were still flowering when we left Saling Hall 40 years later. But now, of course, we are confidently planting lots of better ones. I seem to leave Chelsea every year with a bigger, bluer, stronger variety, many of them evergreen.  Last year’s, from Hoyland Nurseries’ stand, was ‘Queen Mum’, white flowers blue at the base of the petals.  A bit bizarre for a border but grand in a pot. There are no more worries about tenderness – certainly in London.

This the bluest moment of the year for us, if you admit all the purples and lavenders as honorary blues – which allows the geranium of the century, Roxanne, sprawling through half the border, into the picture. Also the pretty, airy Isotoma ‘Blue Star’ in a pot. Crowning them all at present is another plant only recently admitted as reasonably hardy, a solanum we see in the south of France. Solanum laciniatum, Australia’s Kangaroo Apple. It grows on the shady east-facing wall behind the greenhouse door, and in three years has reached over 12 feet, green densely starred with light blue/purple from spring to autumn. The yellow Clematis orientalis is reaching up into its heart.

My only worry is that some of the flowers of the solanum fall into the fish-tank below. The goldfish don’t eat them (two are ‘comets’, Halley and Haley, as in Hale-Bopp. Which is which we’ll never know.) Being potato-related could they poison the water? No sign of it so far.

“You’ll just have to press ‘Go’, they said. ‘He’ll do the rest’. Interviewing a broadcaster as eloquent as Roy Lancaster could be a challenge. How do I press ‘Stop’? I interviewed Roy on the Mound at Boughton House (a uniquely visible spot for an interview) about his latest book, My Life with Plants. The title I would have given it is The Education of a Plantsman, in reference to Russell Page’s masterpiece, The Education of a Gardener. In a sense it’s a plantsman’s equivalent.

I read it (or most of it) at one long sitting. Roy recounts in his unmistakable voice, and in a degree of detail that once or twice reminded me of Patrick Leigh Fermor’s total recall of events 40 years ago, how his schoolboy passion for ornithology was converted one day to botany (or at least plant-spotting) by seeing something strange growing in a potato field. His schoolmaster didn’t recognize it, nor did the Bolton Museum curator, nor the Botany Department at Manchester University.

It was sent on to the Natural History Museum, where it was declared a Mexican species of tobacco plant by no means routine in Britain. Young Roy got a letter from London. ‘Dear Mr Lancaster….’ Roy had found his calling.

From the Bolton Parks Department he was decanted into the Malayan Jungle to do his National Service. The picture of a young man with Bren gun and vasculum studying natural history while confronting the commies sums up the quintessential Lancaster.

Perhaps the most fruitful part of his career was his years at Hillier’s Nursery in the 1970s, as amanuensis to Sir Harold Hillier, and its fruit: the almost incredible Hillier’s Manual, detailing some 7000 woody plants, readably, learnedly, and all too temptingly. In those days you could actually buy the great majority from Hilliers. It was an opportunity some gardeners leapt at. Arboreta were born (including mine at Saling Hall). Then commercial reality broke in; happily in 1977 Hillier’s Arboretum was accepted by the Hampshire County Council as a charitable trust and thrives to this day. Roy’s story goes on with travels to (and books about) China, to Japan, the Americas..….collecting (and converting the plant-blind). Television followed; Roy and Sue made a garden…… It is a lovely story, and a faithful portrait of a lovely man.

The walls are the real driver of a little London garden; you see more of their surface than the diminutive beds. Walls, and pots. I counted just now: we have sixty two planted (not including the green house). Yes, it’s intense; it needs a lot of watering, prinking, daily adjustments. But what else does a gardener want to do? Go abroad, sure. Visit other gardens. You need friendly neighbours and willing helpers. So far, so good. And we’ve learned that a happy climber is worth any number of pots.

This spring I went back to clematis. I’ve seen them in the past as the cherry on the cake; an extra touch of colour on something more structured and essential. What isn’t essential, though, in a garden you can take in at a glance? The trellises that carry the walls up another four feet are the backdrop to all the planting. Neither we nor our neighbours want transparent walls.

One trellis panel has always been bare. There is a mere scrap of bed below to plant in. A Cotoneaster horizontalis reaches up gamely above the wall, but seven feet is a fair stretch even for this marvellously accommodating plant. I’ve heard snide comments: it’s boring, vulgar, even ugly in its fishbone formation. Rubbish: it’s vigorous, designed like no other plant, bright in spring with little white flowers and in autumn with red berries. A little pruning will even make it turn corners. Something evergreen, and rapid, was what we needed to grow through it and on upwards.

Eventually I worked through the options to Clematis armandii, the Chinese evergreen that can become a matted mess if you let it. I won’t. Early progress, though, has been frustrating. Its first long shoot shot up, but not till summer and was still unripe when frost came. It perished. This year three shoots managed five or six feet in April, then stopped. When does it want to grow?

This year’s success has been a lemon-peel clematis, C. tangutica ‘Helios’. The corner by the greenhouse has been more than filled by what the vulgar might call a potato-bush, the purple-flowered Solanum rantonnettii, a cutting from our daughter’s garden in the South of France. ‘Not quite hardy in Britain’ say garden dictionaries. ‘Rampant in London’ say I. It waves slender shoots in full flower, purple on green, high above the greenhouse. Just the place, thought I, for a yellow-flowering clematis. And up she goes.

Rose ‘Bantry Bay’ is the climbing frame for the lightning-fast Clematis viticella ‘Kermesina’ – too red, perhaps to be cheek by jowel with a pink rose. Then I think of Matisse. Two more viticellas scramble with abandon up and through the tangled ivy and Hydrangea petiolaris on the right hand trellis. ‘Polish Spirit’ is a deep, almost brownish purple, hanging in swags. Two or three weeks later comes C. ‘Alba Luxurians’ with its odd white-and-green flowers (or sepals, to be pedantic).

Two other slightly larger-flowered varieties keep the season going: the peerless Perle d’Azur and Prince Charles, like a paler, slightly anaemic version. Oh, yes, and I planted C. wilsonii, like a rather late C. montana, to light up Hydrangea petiolaris on the wall before its turn comes. Finally, to complement an apricot-coloured Chaenomeles I don’t much like, the blue C. alpina. Next year I expect I’ll find room for more.

The ancient Romans had box bug problems, too. No sooner had I written my recent column on the menace of the box-eating caterpillar than I paid a visit to the new herbarium at Cambridge University’s Botanic Garden to be shown, by its curator, Christine Bartram, a box shoot under attack – two thousand years ago. John Stevens Henslow, the creator of the garden, found it in a Roman tomb at Chesterford, near Cambridge, in the 1830’s.

It is difficult to overestimate the influence of Henslow, as a scientist (indeed the very word ‘scientist’ for what had been up to then called a ‘natural philosopher’ was coined by one of his colleagues.) Henslow was Professor of Geology, then Professor of Botany in the University. In the 1830s he developed the new, much bigger botanical garden in the country a mile from the first.

His particular interest, in fact his obsession, was the question of what constitutes a species (and what a variety). The religious view (he became a clergyman) was that God’s creation was, you might say, specific. But when he took his pupils round the countryside collecting herbarium specimens their primroses (for example) were not all identical.

He wondered what this  meant. In planting the botanical garden he went further: there is still an imposing group of Pinus nigra as he planted them, specimens from Corsica, Austria and the Crimea: the same species with quite different habits of growth.  All this was in Charles Darwin’s mind when his tutor, Henslow, declined a berth on the Beagle and nominated Darwin to go in his place. It was the origin of The Origin of Species.

Darwin gave his herbarium, collected on the five years voyage, to Henslow. The university has held their two herbaria, along with, for example, John Lindley’s, for getting on for two hundred years. Then came John Parker, director of the garden from 1986 to 2010. He was determined to tell this story and give the university’s unique herbarium a fitting home. I was briefly involved in a fund-raising campaign (the garden had no public building or education space in those days). I remember our application to the Heritage Lottery Fund was turned down (not enough buses from surrounding schools, if I remember right). The Fund’s offices were two streets away; in summer its staff ate their sandwiches in the garden.

What small beer our fund-raising efforts became, though, when the munificent Sainsburys appeared on the scene. Their Gatsby Trust (the Fitzgerald link eludes me) very much got the idea. It sees Cambridge (with the Wellcome DNA institute nearby) as the world centre of genetic studies. £82 million later the result is a laboratory building like no other, in the garden, a splendid affair of stone and immaculate concrete, to house the iconic herbarium and related studies (also a cafe and facilities for public education). The box? It still has problems.

A sycamore is nobody’s first choice of a tree for a small garden. It’s messy in spring with drifts of pollen and the detritus of flowering. Then comes the sticky deposit of aphids and deep summer shade. The autumn leaves, curling and brown, form useless piles; and far worse are the seeds, obscenely fertile, germinating like grass in every chink of soil.

But we have a big one, seven feet round and fifty high, and no seedlings. Come to that, no flowers. We respect it like a London plane, light up its peeling trunk at night, and suffer its shade – if not gladly, at least patiently. What’s the trick?.

See if you can understand this account of its sex life. “Most inflorescences are formed of a mixture of functionally male and functionally female flowers. On any one tree, one or other of these flower types opens first and the other type opens later. Some trees may be male-starters in one year and female-starters in another. The change from one sex to the other may take place on different dates in different parts of the crown, and different trees in any one population may come into bloom over the course of several weeks.” (This comes from Wikipedia).

Part of the answer is in its fashionable hesitation about its gender. If only it would decide to be a boy how happy we would be. But the main reason it lacks a sex life is that we prune its shoots back brutally every winter to limit its spread over other people’s gardens (and our own). I suspect its wood never ripens enough to get to the flowering stage. It’s an expensive solution.

“Best of Show’ is always a well-debated subject, and Trad’s annual Chelsea award, over several decades, has not always coincided with the official verdict. This year my friend James Basson, who scored so highly last year with his delicate evocation of Provence, was given the gong for his Maltese quarry. It was a memorable image, dominated by its ziggurat or cenotaph, but how it qualified to be called a garden I’m not sure. The plants were chosen with absolute botanical rigour, but I fear most of them were what friends call BIO (for Botanical Interest Only). Perhaps the spec for entries doesn’t mention ‘garden’, though heaven knows it’s a broad category. Sadly there was less competition than usual this year: the RHS had to fill the empty spaces in the Main Avenue (and frequently elsewhere, even in the Great Pavilion) with champagne bars.)

Trad’s Best of Show was tucked away among the ‘Artisans’, by the woodland picnic area in Ranelagh gardens. I’m afraid most visitors will have missed it. A pity; it was a piece of Japanese artistry worth going a long way to see, and almost never seen outside Japan. The designer, Kazuyuki Ishihara, has won gold here before, but this year’s tiny jewel was exceptional, in concept, in truthfulness, in precision and in expressing such a love for its materials that I found it moving. Even the back of his stand was exquisitely gardened.

The other moving moment of the day was Michael Heseltine’s speech at the President’s lunch. He started ominously by telling us there were no jokes coming, then in ten absorbing minutes told us why gardening matters and what we should do about it. In a sense we have heard it all before. Give a schoolchild a bean and they will never forget seeing its first leaves pop up. The moral effect of engaging with the natural world.

‘Gardens’, he said, ‘in whichever form, are expressions of ourselves. They are statements of pride and responsibility. They are definable spaces often requiring easily acquired skills. They provide talking points for communication with neighbours. They impose a year round discipline. They provide a therapeutic escape from daily pressures.’

Lord Heseltine has worked hard and persistently on the revival of communities gone to the dogs. He has huge experience in the hard slog of restoring hope and pride, work that is long on boring admin, tricky politics and often slow returns. He is totally convincing on the need for life-changing inspiration, hard to conjure, patchy in its results, but vital in ‘helping people feel a sense of purpose, an interest in what their life holds. There are no simple answers to complex questions, but gardening can play a part. Derelict land is all too present. Provide them with the tools to plant it. If they plant it they may feel a pride in what they did. They may wish to defend it, even extend it. The work requires little skill but it offers ladders.’

His sentiments and a piece of loving artistry made me leave the showground with a sense of fulfilment – and a sense of purpose.