I can think of a dozen reasons for visiting New York in October – the best month in this continent of extreme weather – but the one that comes uppermost in my mind is the Conservatory Garden in Central Park

I know I bang on about Central Park, probably once a year, but then it has qualities none of our London parks (I love them too) can match. Seemingly endless paths (trails sounds more American) among huge grey rocks like monster whales and enormous trees, across savannah, skirting lakes and ponds, leading to cafes, kiosks, the boathouse restaurant, the zoo, the auditorium…. and several gardens. The Conservatory Garden, the most accomplished, the most formal and the most complete in itself, is way up around 105th Street, almost in Harlem.

Its centre is an ‘Italian’ design – though it would be hard to find avenues of crab apples around a simple level lawn in Italy. The ‘English’ third is the most intimate, cloistered among yew hedges, sheltering a bronze of Mary and Dickon of The Secret Garden, reflected in a little waterlily pond.

The ‘French’ garden is the October event: an overwhelming display of Korean chrysanthemums, a bank fifteen feet wide right round a rectangular piazza, enclosing the city’s jolliest fountain; three mischievous and nubile young ladies dancing round the water.

The chrysanths were a gift to the city in 1947 as a war memorial. The donor was Mary Lasker from Chicago, a huge benefactor of medical research. They were originally grown from seed, a strain developed by the Park for decades, selecting a wonderful palette of brilliant colours, orange and violet, yellow and white, red and brown. Other gardens show them oriental-style, extravagantly coiffed into pompoms and cascades. Here they are grown as they would grow in some dream meadow, a random medley, not pinched and primped but tilting this way and that, jostling, playing like the dancers round the fountain.

These days I’m told they are grown from cuttings and planted out from 2,000 pots in late May. Not that they are tender, even in New York winters, but they replace the spring bedding of 20,000 tulips. They draw New Yorkers like a baseball game. I’d love to see a really full-throttle Mum Show in England.

The sun is low enough in the sky this afternoon to rub in just how little light our new garden will get in winter. There will be improvements: the overhead shade of the huge sycamore and big walnut is going to be massively reduced. But this is looking forward several seasons. Half the garden will see no direct sunlight all winter.

I am turning over various possibilities in my mind. Portugal laurel, ivy, aucubas and some snazzy box topiary were our predecessors’ solutions. But I crave a smooth restful green patch; the equivalent of a lawn, which would never thrive here. Is a moss lawn a practical possibility, I wonder? I dream of the green tranquillity of the moss gardens of Japan. But does it need the warm wet climate of Kyoto?

Look up ‘moss lawn’ on the internet and every reference is about getting rid of moss as a nuisance. The only pro-moss site I can find is Gardens Inspired, from somewhere unspecified in the (I suspect southern ) States. Debra Anchors gives recipes for planting a moss lawn: literally recipes; they involve scraps of moss collected from nearby put in a blender with either yoghurt or beer, then sprayed on to bare ground and watered until it goes green. I love the idea. Worth an experiment, surely? I’ve heard it said, too, that regular spraying with Round-up can encourage it .

Alternatively, if I do nothing, our current modest crop of mind-your-own-business, the pretty little Helxine (or Soleirolia) soleirolii, will pretty soon do the business for us. Its tiny bright green leaves are the terrestrial equivalent of duckweed. They say it is almost equally pernicious, delicious though it looks in the interstices of old greenhouses.

Now that the squirrels have almost finished chewing the walnuts on our neighbour’s tree and dropping the remains on our garden they are starting on our pots of bulbs. I have been planting pots in anticipation of the greenhouse we are excitedly expecting in a week or two, using what is left of our collection of wonky old handmade ones. (I scan old garden sheds, greenhouses and shops selling bric a brac wherever I go, hoping to find these increasingly rare veterans).

Narcissus seem to be the squirrels’ first choice, with Iris reticulata also popular and snowdrops an acceptable snack. Do tulip bulbs have less scent, or is it because I plant them deeper that they have (so far) been relatively unscathed?

The brick base of the greenhouse is all ready, a (very) minor masterpiece in reclaimed London stock bricks in their characteristic medley of gentle colours: yellow, pink and grey. It is already hard to distinguish from the surrounding garden walls. The bricklayer who built it is from Croatia; a gentle smiling man with not much English. When I told him how I intended to fill it with flowers he said “I like this job. I like flowers very much. At home I have flowers everywhere; in the hall, in the kitchen, on the walls. People say I am like woman’.

Where is this, and what is it called?

The Royal Parks are so important to life in London, indeed to the whole identity of the city, that I feel ashamed I knew so little about them; how big they are, how many, and how they are run. Linda Lennon, the Chief Executive responsible for them, came to the AGM of the Metropolitan Public Gardens Association the other day (I am the current president) to enlighten us. Let me pass on some of what we learned.

The total area of the parks is 5, 000 acres, of which Richmond Park represents a half and Bushy Park another 1,100 acres. There are eight in all, and seven other non-royal green spaces (Brompton Cemetery is one) run in conjunction with them. They claim 40 million visitors a year – surely a huge under-estimate (though are you a visitor if you simply walk through on the way to your bus?)

They estimate there are 135, 000 trees, of 250 species. Again, how do they count them, and how big to they have to be to qualify? The parks encompass 15 miles of river and contain 280 statues. Regent’s Park and Primrose Hill taken together are the biggest in central London, covering 395 acres (of which 100 are dedicated to sports). Hyde Park covers 350 acres and Kensington Gardens 242 – so taken together they far outweigh the Regent’s Park area. St James’s Park covers 93 acres – but this includes the Mall and Horse Guards Parade. The Green Park, the most perfect and consistent in character (but this is only my opinion) is a mere 53 acres.

All of them together cost £32 million a year to maintain, of which the government pays £18 million – and going down. They employ (a mere) 110 staff, and gave up having their own propagation and production departments in the early ’90s, to the delight of the Dutch nursery business. It is hardly surprising that pop concerts and other crowd-pullers are put on more and more often. Linda told us that this year’s noise-reduction at a big bash produced an unexpected result: complaints from people living nearby who had invited their friends for the evening that they couldn’t hear the music properly any more.

The deer are nibbling the grass just outside the window as I write. Two does and a faun that can’t be more than a few days old. Four more, with one buck, are showing their white backsides as they graze the meadow a hundred yards off. They don’t know it, but they’ve just won an argument. The broad meadow below the house, 18 acres dipping down to the Lymington River, will be theirs. Their private park. My foolish idea of a landscaped arboretum goes in the bin.

Young trees and deer don’t mix. I learned the lesson the hard way in France years ago, when my landscaping ambitions were foiled again and again by game of various kinds.

Red deer are more formidable than roe deer, and boar worse than either to a tree- planter and dabbler in streams and ponds. At Saling Hall we had a few visitors, and far worse, muntjac, but managed to handle them on our 12 acres. Here in the New Forest there seems no point. Indeed the deer are the point – originally of the whole forest.

And would a meadow dotted with new trees, however interesting or rare or fiery in autumn, really be more beautiful than a little green park with deer and the few scattered old oaks we have here? Certainly not so appropriate. We (that is our daughter’s family) have a splendid piece of old oak woodland above the meadow. Gentle thinning of the big trees (and clearing of ponticum) will give us forest fringes to adorn with a few new trees I will have to choose with maximum deliberation and protect with scrupulous care. And I shall have much more time to enjoy the wild life.

We visit the agreeable old village of Cotignac most years at the end of summer. It lies among the steep pine-covered hills of the Var in the region justifiably known as La Provence Verte. The green is a blend of light and dark; the pure pale green of the Aleppo pine the dominant shade (what tragic thoughts the name of this lovely tree bring to mind today). The dark notes are mainly oaks of half a dozen species, with here and there the exclamation marks of slender cypresses.

Last year I was delighted to discover, the day before departing, an exhibition of the photographs of a colleague of long ago when my career was in fashion magazines. Frank Horvat was an international star at the time when David Bailey and Brian Duffy and their East End friends were making Twiggy and that girlish group famous. Frank took sexier fashion photos than any of them. He remained detached, though, a little aloof, and never became the same sort of “sleb”.

A few years later he made his dissident views plain by publishing a beautiful, even moving, book of portraits of trees. His trees, or most of them, stood alone in fields, on bare plains or mountainsides, sometimes distorted by the prevailing wind, usually just a clear statement of their heredity, their race, fully developed and ready to be admired.

This year I tracked Frank down to his cottage high in the hills above Cotignac, at the very end of a winding dirt road on the lip of a frightening ravine. The stone building, in its clearing among ancient olives, commands an immense view: nothing but forest in rippling ridges, 180 degrees wide and perhaps forty miles deep, to the irregular blue line of the Massif des Maures that overlooks the sea between Toulon and St Tropez.

In his eighties Frank has discovered the internet and realised that it offers his life’s work the chance of a revival. His work could never readily be classified. He puts it, in a book to be published next month, in fifteen categories or ‘keys’, but none of them truly categorical in anything but pictorial terms. Google his name to see his pictures.

I found the meeting, the rediscovery of an old friend and his survey of his own achievement a moving and thought-provoking experience. He has written his observations of the world in light (the literal meaning of photography) over a span of some seventy years. He has ranged from salons to slums, recorded chaos and captured calm. No philosophy emerges from his pictures; he is as free from judgement as Candide, and as free of conclusions – unless you call Candide’s last word a conclusion: “Il faut cultiver son jardin”.

Autumn never announced its arrival more clearly than by today’s damp chill after two days of almost unprecedented late summer sun. We have had our little garden sprinklers on every night for weeks; without them I’m sure there would have been no growth in the garden at all. The climbers thick on the walls (and the roses thrusting six feet above them) suck all the water from the ground. I don’t grudge it, but I must replace it.

Meanwhile preparations are afoot for our new greenhouse. They

started in May when we cleared the biggest bed in the garden (be under no delusion; it’s tiny), digging out, skimming that bilious yellow-leaved spirea, a red-leaved maple, a clapped-out pittosporum and a tall hibiscus. The hibiscus is doing well on intensive care in another spot. A neighbour accepted the maple; the rest went on a skip. We had to remove 80 bags of soil (through the house, of course) to lower the ground level for the future greenhouse. The plot has been filled with potatoes, runner beans, courgettes and salads for the summer. Now comes the prospect of building the base for the house, due to arrive in November.

It is a little gem of an aluminium greenhouse from Alitex; three-quarters of a span, the third quarter resting on the western garden wall. With its finials and its little spiky ridge it will look (we hope) as Victorian as if it came with the house, but need minimum upkeep. There are quite a few plants in pots waiting impatiently for its arrival before winter sets in.

It’s forty years now that I have known the Banks family’s garden on the Welsh border – almost a quarter of the garden’s long life. Four generations of Bankses have been passionate plantsmen and distinguished dendrologists. William Harland B, who bought Hergest Croft in 1912, was inspired by William Robinson and an eager customer of Veitch’s Exeter Nursery when EH Wilson was among those scouring China on their behalf. Many of his introductions thrive here still.

Just how and why the 40 inches of rain, neutral loamy soil and the altitude of 700-odd feet allow or provoke the mighty growth that gives Hergest Croft so many champion or near-champion trees is unclear. I am inclined to give as much of the credit to their proprietors. The biggest plants tend to belong, naturally enough, to those who planted them first.

I was at school with Lawrence, the third Banks to own the garden, and sat at the feet of his father Dick – a wonderfully benign authority. It is easy to see why plants should want to reward such dedicated and expert overseers. Lawrence was Treasurer of the RHS for many years and his wife Elizabeth its first woman (and first horticulturally professional) President until earlier this year.

Today the garden and its adjacent Park Wood are best known for their National Collections of maples and birches. It is easy to be distracted, though, by the awesome firs and pines, oaks, limes and walnuts, ashes, larches, cedars and far rarer things that tower in the arboretum and shade the sheep in the park-like farmland around.

Elizabeth Banks Associates is one of the foremost landscape practices in the country. Is it despite or because of this that there is no sniff of modern or fashionable design to be seen? The Hergest garden remains largely as it was conceived a century ago, its structural elements disguised, of course, by the growth of what were once almost incidental trees and shrubs. Now they spread their branches over path and terrace and hedge. How many gardens, though, keep the deliberate unadorned geometry of orchard and vegetables, soft fruit and perennial borders, greenhouses, rose garden and tennis court, almost in the manner of a farm, where function needs no justification?

How calming it is; how unaffected and truthful. Do you detect a partiality here? Can you tell that I find Hergest Croft one of the holy places of horticulture? I don’t deny it.