To Wisley for a day’s immersion in limes, trees as easy to spot as they are hard to tell apart. I don’t usually delve this deep in botany, but when the R.H.S. Woody Plant Committee convenes a Study Day you are guaranteed the best and most experienced minds in the business: a taxonomic Test match.

In a barn-like building lined with specimens giving off the sweetest smells we spent the morning studying stellate hairs. There are 20+ species of Tilia in the world (the final count is pending; we shall be kept in suspense until the imminent publication of his Tilia monograph by Professor Donald Piggott, the gnomic leader of our discussion). Most of them come from Asia; where one species ends and another begins, either geographically or taxonomically, seems to remain pretty moot and is mainly determined by the hairs, if any, stellate or otherwise, on the underside of the leaves.

We have three native Tilia species in Britain (again, subject to the usual caveats), the small-leaved, the big-leaved and the common or hybrid limes. You know the common lime by its propensity to sprout from the base or anywhere up the trunk. We forgive it its messiness for its eventual monumental shape and size. Where exactly the dividing line between its two parents lies is less clear. It is some comfort to know that the herbalist Gerard’s Tilia was actually an elm, and that even the great Linnaeus’s type plant for Tilia was the hybrid T. x europaea….

My particular interest is in their offspring. In the past five years one or other of the three has been regenerating in the garden here. The trouble is that the saplings seem to correspond with none of them. They have larger leaves than T. cordata and hairier leaves than T. platyphyllos. On the other hand their young wood is purplish, not green like T. europaea. It’s back to the hairs and the magnifying glass, I’m afraid. But shall I grow them and cherish them? Of course, whatever they are.

The end of summer has many hints and indications, but yesterday two of them stood out like signal flags. First was the cyclamen, in a dozen different places but unanimous about the date to start flowering. Second was the underfoot crunch of crab apples as we played croquet. Should there be a John Downie rule? Probably not: it’s the same hazard for everybody. Clearing them off the grass is not an option; the tree rains its red and yellow fruit for weeks on end, too small to rake up. The proper procedure is probably rather like the olive crop, involving sheets, shaking and beating the branches, with a fragrant cauldron of jelly at the end. But now there is harvest everywhere: plums and gages still, apples starting, raspberries and tomatoes, wine berries that have seeded in half a dozen places, blackberries in the hedge (it’s a good year already) and huge puffballs attracting your eye like wind blown plastic bags.

It’s a strange creature, the puffball; a mushroom apparently crossed with a cheese. We started on a 4 lb monster at breakfast yesterday, frying thin slices in the pan after the bacon until they were golden brown and slightly crisp. The flavour is mild mushroom and the texture when you cut and slice just like a huge curd cheese. I made the mistake though of leaving this beautiful white football in the sun all afternoon. By evening there was a ripely cheesy smell, the cut surface was turning yellow, and to jettison it was the only course.

Better I believe to pick them at croquet ball size and keep them in the larder while you intrigue your friends with their mysterious savour. Some people cook them with oil and garlic. I have tried them raw but found them rather dull and pappy.

The dormitory suburbs of London have obliterated countless historic gardens. I still remember with a shudder witnessing the last moments of Stubbers, the house on the London fringe of Essex where the botanist / brewer William Coys, in Queen Elizabeth’s reign, grew the first yuccas, Jerusalem artichokes and ivy-leaved toadflax in England – and much else besides, I expect. Humphry Repton did a Red Book for subsequent owners, the Russells. Napier Russell took me to watch workmen from Havering Council break up the black and white marble floor of the conservatory with sledge hammers, before they leased the park for gravel extraction.

All the more wonderful, therefore, to visit a similar house that survived. Valentines is as marooned as it could be in the centre of Ilford, half a mile from the North Circular Road and surrounded by the sort of villas that seem to reproduce themselves in this country, generation after generation, their genes recklessly blending Tudor with Moorish and cottage with Bauhaus.

Valentines has not only survived a hundred years as a council owned white elephant, used as offices, for refugees, as surgeries and a school, it has kept the garden and a great deal of the park laid out around it from the 17th to the 19th century.

Ten years ago Redbridge council engineered two Millennium Lottery Fund grants, one of £3 million for the garden and another of £2 million for the house. This spring it opened for business as a sort of council-owned stately home. It is exceedingly well done, both the house and the garden, which is a rare example of an early 18th century landscape, complete with a long canal, patte d’oie, two shell grottoes, walled garden, a lake and some remarkable trees.

The curator, Nigel Burch, has found an admirable compromise between the demands of a public park and the aesthetic of a country house. Old box hedges in the walled garden brims with the plants of our time in bold decisive blocks. If future landscapes emerge from the humdrum streets of Ilford Valentines will surely deserve the credit.

I am not, heaven knows, a serial conspiracy theorist, but let’s just suppose that, like the Millennium Bug, this flu pandemic is run by someone’s P.R. department – in this case of the pharmaceutical industry. The papers can’t turn down flu stories. The genius who gave it its rather nasty name should be getting royalties. So far (and I’ve got it) it is not nearly as bad as the common winter kind. Lots of people die of that, remember.

Now I’ve started, I’ll go further. It seems to be taken for granted that we are all scared to death of death. Few of us look forward to it (and they, of course, can be criminalized). 200 of our army have died in Afghanistan to ward off (we are told) a repeat of 50 dying in London.

Don’t let me start on Iraq. I’ll stick to us, and the sterner stuff we used to be made of.

Better still, to your relief I’ll return to gardening.

You don’t need to be a follower of Nigel Lawson or Ian Plimer on the question of climate change to demand a rather more rigorous use of evidence. Gardeners are assumed to be soft in the head. An editorial in this month’s The Garden is typical of the confusion that is served to us as gospel. The headline is ‘Climate change may finish Cottage Gardens’. It then quotes an official from the Met Office saying ‘It is quite possible our gardens will look really different in 20, or certainly 50, years from now.’ It certainly is.

The report then shifts to 70 years hence, ’in 2080’, when ‘if no steps are taken to curb greenhouse gas emission,’ average summer temperatures are ‘likely to rise more than 4° C’. According to Hilary Benn, the heatwave in 2003 saw ‘average daily summer temperatures 2° C above average,’ ’estimated to have caused an extra 35,000 deaths in northern Europe’. Clive Lane, of the Cottage Garden Society, ‘has already seen …… primulas and violets struggling to survive.’ At Rosemoor Chris Bailes is happy to see Tetrapanax payrifera thriving, ‘though Rosemoor is in a frost pocket’. Same here. If more evidence of global warming were needed, the exciting new feature at Newby, well north of York, is an avenue of olive trees. My doubts about this are more aesthetic than meteorological.

We have been lucky, over the past 26 years (since the winter of 1982/83 in fact) to have got away with growing plants traditionally labelled borderline for hardiness. Last winter was too cold for a few. But to extrapolate from gardeners’ experiences to global trends is absurd, and the R.H.S. should know better.

Just home from our woods in North Wales with a glowing sense of achievement. We have left something for posterity: not more trees, but a feature that could be puzzling archeologists centuries from now.

It starts with a pond, mere or tarn (the Welsh llyn seems to make no distinction). A body of water, anyway, some hundred yards by thirty, that I made eight years ago by damming a stream through a new plantation of spruce and pine. This is up in the hills, at 700 feet or so, overlooked only by the heathey ridge of the Rhinogs. There is a forestry road, but no footpaths. As soon as I made it I wanted to swim in it. The bottom is soft, though, and there are snags of old roots to discourage you.

So I planned a wooden jetty with a ladder to get me out into the deep water.

It would look slightly mysterious, as though it was expecting a boat. When I got there last week, though, I suddenly saw a better answer. We had drained the pond to explore the bottom. These hills are full of huge flat stones. We could make a flight of steps up from the depths to the sedgy bank. There is a famous path of steps like this in Cwm Buchan, ten miles north, attributed in legend to the Romans.

What would the Romans have done if they had had a Komatsu? This massive engine, in the right hands, can arrange ton-weights as delicately as pieces of marquetry. Wyn Owen, who owns the surrounding hills and the sheep that mow them, could part two blades of grass with its huge bucket. He spent a morning unearthing slabs, shaking them free of earth by tossing them in the air and catching them. In the afternoon, with the blue water of Cardigan Bay in the background, we placed them to form seven giant steps from the bottom of the pond to the bank.

It will have to fill again from the stream before I can run down them, splash in and swim away. The idea fills me with excitement. I understand the pleasure Richard Long (now at Tate Modern) gets when he leaves his traces on nature.

The giant woodpecker I heard in the trees at the end of the garden turned out to be a BT engineer up a ladder making adjustments to a telegraph pole. It was planted, he told me, in 1945, and still good, apparently, for another ten years or so. He explained how to read the labels that tell you the pole’s age and height, a skill I immediately put into practice on every neighbouring pole. My best find: the one that carries my calls over the moat from the house to the road – dated 1934 (and 26 feet high). It doesn’t say whether it’s pine or Douglas fir.

I hurried back to ask my woodpecker friend if 75 years is an unusual lifespan. ‘Pretty good’, he said. ‘We’ll have to change it soon, but it’s still safe.’ ‘What about the new ones?’ was my next question. ‘Hopeless.’ he said. ‘They don’t season them or pickle them properly any more. They used to age them for two years, then pickle them in creosote. Now they’re just fresh trees given a pressure treatment with wood preserver. I have far more trouble with the new ones.’

I wasn’t surprised. Telegraph poles are not the only timber that comes green, unseasoned, not properly treated and ready to rot. We’ve had to replace a gate post after three years. Does no one believe in the future any more?

The least welcome sound to any gardener? Four syllables: honey fungus. I suspected it the moment I saw the rose that accompanied my working life for 20 years, three feet from my desk, winking its harlequin flowers at me all summer through the window, sicken and, within ten days, die.

It was the so-called climbing form of Rosa mutabilis, the slender Chinese rose that changes colour from orange in bud to deep crimson-pink as the simple wide-open flower, once pollinated, fades and falls. I planted it in the wall-corner to the left of my window, knowing that its slender structure of smooth purple stems would not get out of hand and that its flowers would entertain me for much of the year. I liked its story, too, as Graham Stuart Thomas tells it. It was given by Prince Borromeo, the fortunate gardener of those two romantic islands in Lake Maggiore, Isola Bella and Isola Madre, to Henri Correvon, the Swiss botanist whose Flore Alpine excited me in youth like no other flower book. When you see this plate, one of his friend Philippe Robert’s illustrations, you will see that it lies at the heart of what we call Art Deco. Robert did not paint Rosa mutabilis, alas.

My plant on the wall grew to nine feet, hardly qualifying it as a climber, but beautifully framing the window, invaded from the other side by grape-vines.
The rose is dead and the vines are sick. Wisley confirmed that the root I sent to the pathologist was killed by Armillarea mellea – though its black bark, peeling off to show a layer of white mycelium, was scarcely open to other diagnoses. I remembered then that the Japanese anemones in the bed under the windows had once grown so tall that I peered out through their white flowers and vine-like leaves; then next year had barely reached the sill. That was nearly 20 years ago. Had the malignant fungus been lurking along the base of the wall all this time?

The document that the R.H.S. sends out to victims is full of data but little encouragement. The black bootlaces of honey fungus can travel a metre a year, they say, and reach as far as 30 metres. I look despairingly round at the plants within a 30-metre radius. They include magnolias (susceptible), a cedar (highly susceptible), a number of roses, a quince, a crabapple …….. Do I see wilting shoots, or just imagine them?

‘There is no treatment available’ goes the usual rubric – with a subtext, I always feel, of ‘to mere gardeners like you’. Bray’s Emulsion, the old panacea, has been condemned as unsafe (or at least, by E.C. standards, untested). How many gardeners has it killed or disabled? I think we should know. You can still get creosote, a rough and ready version, but woe betide you if the police sniff it around your plants.

Meanwhile the ancient grape vine on the gable is dying, and the next one along the front of the house is looking poorly. Does some witch-doctor know a spell?