I think I’ve written before about our friend Dottie Ratcliff, whose practice in her serial tiny gardens is to leave nine inches between plants. Some of her fruit trees admittedly look a bit pinched, but they still bear good crops. The total effect is (shall we say?) bountiful.

I am modifying her plan. Nine inches is a bit tight for most shrubs, even in this little garden. On the other hand 4 1/2 inches seems about right for smaller herbaceous things. I’ve just put Iris sibirica ‘Flight of Butterflies’ nine inches from Verbena bonariensis with Geranium ‘Rozanne’ in between. When you see it in plan (as you do when you’re looking down on the bed you are planting) it looks much too crowded. But it’s the elevation rather than the plan that matters: the airspace the plants fill, rather than the space in the ground.

By interspersing your high-rise plants with lower ones you will see their profiles from top to bottom. Some, it is true, have little elegance near the ground, but irises, for example, and Japanese anemones, and the lanky V. bonariensis, and the trim-figured Campanula persicifolia, and foxgloves, and thalictrums and aquilegias and …and…. are at their best seen rising from other plants that creep or loll. Certainly the greedier roots will win, but plenty of food and water will keep them all happy for a season or two.

There is also the problem of shade, as one plant shades another – which is more acute in a garden like ours which is already deprived of light. I seek reassurance in the comfortable figure of Margery Fish, whose Gardening in the Shade is still beside my bed. The shade she talks about is largely from trees, of course, rather than London terraces and walls. (We have both varieties). Her plant lists, though, are up-lifting. Besides such obvious candidates as hellebores and pulmonarias she invites us to grow aquilegias, heucherellas, tellima grandiflora, practically any campanula, thalictrums, most geraniums, Japanese anemones, viola cornuta, daylilies, peonies, aconites, monardas, lobelias and phlox, which she says is ‘really happier in shade’. For grey leaves artemisias, she says, do well. Phlomis samia is well-known as a shade plant…. and on it goes. Her list, as you see, seems to include most perennials. The word to look for in her eloquent writing is ‘light’. Mrs Fish scatters it around to qualify ‘shade’ to a degree that might make a more timid soul than me nervous.

Notwithstanding, I shall try as many as I can fit in – and, of course, report on progress.

Whether last night’s frost, the first of the spring, did for the magnolias at Kew I don’t yet know, but I’m glad I went to see them last week. A sense of urgency, the feeling that the sunnier the weather, the greater the danger that the flowers will be clobbered, is what makes them so poignant. To expose so much bare flesh so early in the year is provocative.

The trees around are still wintry bare, buds swelling perhaps, or catkins, or showing a few tentative little leaves. Magnolias get their kit off. The star of the show last week was Magnolia kobus var. borealis, as its label describes it. If the label department were to keep up with shifting taxonomic opinion on every plant it could be a costly business. The status of kobus as a species, the legitimacy of the name (one botanist pointed out that the Japanese name is Kobushi), its relationship with M. stellata, M. salicifolia and M. x loebneri have all been disputed – and not always in the friendly spirit you would hope it would inspire.

Nor is it clear, at least to me, how the form labelled var. borealis fits in – except in being big and incredibly beautiful. Does it come from further north, as ‘borealis’ implies? There will be someone at Kew who knows. There might even be someone who remembers planting it and waiting, maybe twenty years, for it to flower.

I only hope the flowers weren’t fried by the frost last night.

I should have been ready for planting time, with all my plans laid and drawn up, plants ordered and a serene sense of purpose reigning in the garden. Then suddenly it’s here, a good month early, everything springing into growth, Rassells nursery over the road a jewel box of newly-arrived temptations. Plans? I’m borrowing their barrow to ferry over far more plants than I can reasonably fit in.

I’ve strained my back crouching in our restricted spaces, shoe-horning campanulas among anemones among veronicastrums among geraniums. Verbenas, too. Oh, and of course white foxgloves. I pounce on what looks like a clear space only to remember that’s where a hosta lies buried. Magnolia petals rain down on me as I dig (in this temperature the flowers won’t last long).

It’s the usual question: what shrub will grow in a droughty two-foot space at the foot of a sizable sycamore, tolerate its sooty drip, perfume the spring, flower in summer and flare up in autumn? I know the answer; accepting it is another matter, though.

What is surprising as I plant is how few roots I find. Surely the roses, hydrangeas, ivies, pileostegias, clematis, cotoneaster and the rest of the dense hamper on the walls forage far and wide for moisture. Often, within feet of a substantial climber, I find quite open and available soil. I quietly hope all the roots are next door.

Magnolia soulangeana, Cercidiphyllum japonicum 'Pendulum' behind.

This won’t be news, because we’re all experiencing it – in England, that is – but a diary is for putting things on record, and a record is surely what this is. The Magnolia soulangeana over the front door was shedding its bud scales and turning purple in the last week of February. Last year I noted its date: April 14. Six weeks is a quite a leap.

Japanese maples (some of them) are opening their leaves, our precious cercidiphyllum is turning its special shade of russet-going-green, and Jasminum polyanthum, which usually waits until February in the conservatory, is flowering in the open air. There are anomalies wherever we look; most of them welcome. The fear of frost is acute, but all the more reason to enjoy this absurdly precocious spring.

The hawthorn is supposedly the harbinger of clout-casting in May. I have planted two, in tubs flanking the door from my top floor study to its tiny roof garden to shade it from the summer evening sun. They have been harbinging away like billy-o for two weeks now. Did I plant the Glastonbury thorn (C. monogyna ‘Praecox’) by mistake?

Last month I illustrated a double pale pink camellia that flowered here just before Christmas, and asked for its name. A faithful Japanese correspondent has obliged. It is apparently ‘High Hat’ (who gives them these banal names?), a sport of what the Japanese consider the greatest camellia of them all: Daikagura, known to have been bred before 1789. The name means the sort of dance ritual performed in spring in remotest Japan to ward off evil spirits. My pen-friend even sent me a video-clip of country-folk capering in dragon kit.

“High Hat’ (it has the virtue, among others, of dropping its flowers promptly when they’re over) in turn begat ‘Conrad Hilton’. As my friend says, from 600-year-old folklore to hotel magnate via two flowers. Japan. meanwhile, has been shivering in the opposite to our weather. Poor Yamanashi, the prefecture with the vineyards near Tokyo, recently caught 114 centimetres, or 3′ 9”, of snow in one night. Another record.

The Riviera experiments with succulents; Morocco glories in them. In Marrakech, 1000 miles further south, the world of cacti and agaves, euphorbias and all the swollen desert-dwellers is a playground for gardeners’ wildest imaginings. It seems they like fat living after all, these prickly things that look so ferocious on the edge of survival in wind-blown wastes. In the gardens of French couturiers and Italian tycoons a cactus can be voluptuous and its spines fashion statements.

The Jardin Majorelle in the heart of Marrakech was the work of the painter Jacques Majorelle more than 70 years ago. Its survival, and its present state as an attraction drawing 700,000 visitors a year, is due to the late Yves St Laurent. Nurture at this level of precision is something I associate with Japan rather than Africa. The very soil, its immaculate beige grains carved into ridges, into perfectly-smooth terraces and gentle basins for irrigation, is a work of art. From it arise the sturdy pillars or the graceful curving stems of palms, and in their delicate tracery of shade shapes of succulents so strange that they might have been invented in Disney’s studios. Smooth blue leaves, waxy, warty, wrinkled, knobby, fasciated, absurd contorted shapes, or rosettes so regular and refined they seem still to be on a designer’s drawing board. Planes of water like glass or gently stirring. A tinkling jet here in the sun, there a generous gush in the dark of a bamboo grove. And brilliant colours that need the brilliant sun to make them bearable: orange and searing ultramarine, lemon yellow and deep Moroccan red.

The International Dendrology Society has the entrée to some very private gardens. We visited half a dozen, including the sumptuous villa of Yves St Laurent’s partner Pierre Bergé. This was a super–privileged tour of a world that pushes the possibilities of plants as far as skill and artistry and money extend. What is even more striking about Marrakech, though, is the size and splendour of the public gardens being created along boulevards and in parks around the edges of the cramped and bustling town. There seems to be hardly a road that is not an incipient avenue of palms. King Mohamed loves gardens, too.

One person says La Mortola is on the way up; the next visitor says it’s worse than ever. It’s been like this since the 1980s, when a posse of busy-bodies, largely from the RHS, (I was one, but the one that counted was the much- admired Director of Wisley, Chris Brickell) took action. The staff at this famous garden, the creation of the same Hanbury family that gave the RHS the land for Wisley, had gone on strike. The Hanburys had sold the property to the Italian state, little thinking what a mess Italian bureaucracy can make. What had been one of the world’s best sub-tropical gardens, a superb botanical collection on the borders of Italy and France, at the very point where the Alps collapse into the sea, so steep and sea-surrounded that frost never comes, was a weedy chaos, under soaring palms and cypresses and far rarer trees.

On my first visit the striking gardeners were camping in a cave-mouth near the monumental entrance. Negotiations followed, with British botanists setting new standards for organisation and maintenance: eventually the University of Genoa took responsibility. The question is, how are they doing?

The other day I was pleasantly surprised. The garden covers 18 hectares. You can’t expect perfection. But the most exceptional parts, collections of succulents and cycads in particular, are well weeded, cultivated and surprisingly well labeled. The whole garden looks in good health – even the lower reaches towards the sea where the citrus orchard is crisscrossed with pergolas. There are areas of long grass and weeds, but no dereliction.

There was one black moment, though: the discovery of a new (to me) and horrific predator on the box plants. It is a moth (Cydalima perspectalis) and its yellow, black-spotted caterpillar which gobbles box leaves and shoots until the plant is bare. “Piralide” is its vernacular name. It arrived in Europe three or four years ago, in Italy last year, and has (as you have guessed) no authorized treatment. One French gardener I know has gone on a spraying course to be ready for action, but the red flag is hoisted. What will it make of our island’s weather, and miles and miles of box hedges, I wonder.

Just home from the afternoon at Kew, to see the beautifully staged orchid show. Where do they hide these magical creatures the rest of the time? Marshalling such feats of cultivation to dramatize their story is a brilliant idea: crowd-pulling, absorbing….. a triumph. Even without the orchids, though, it would have been with the journey to see the seas of humble crocuses jostling in the wind.

The little ‘Tommy’, Crocus tommasimianus, beats the snowdrop in charm, simplicity – and in coming first. This year, in fact, even before the snowdrops have woven their carpet. I’m not sure how, or even why, its varieties (Whitewell Purple, Barr’s Purple…) are distinguished. Infinite nuances of colour are the attraction of the crowd.

Are the individuals different, and does it matter, when the tops and bottoms of their petals, darker and lighter, mauve and silver, are rippling semaphores across the grass?

Even better, though, is their performance as pampered prima donnas indoors, in warmth and light, where they grow to double height and spread-eagle their petals to flout their sex. I grow them in old clay thumb-pots and put them in the centre of the dinner table among the candles. They tilt and topple, gaping wide, purple, mauve and white with stamens golden in the candlelight. They last three days like this, but for this time they outshine (forgive me, orchids) any other midwinter flower.

The more you divide up a space the bigger it becomes. Scientific or not, I call it the Law of Immediate Surroundings. Your sense of space depends on what you can see; the only reason why tiny bedsits are habitable is that your vision accepts any limits you impose on it, and the rest of your senses, however reluctantly, follow.

I muse on this whenever I go down an arterial road lined with tiny houses cowering (if they are lucky) behind fences or hedges. At a pinch, I think, I could be content to make one of those cramped front rooms my space – because I could block off the outside world. My immediate surroundings are all I see. I could be snug.

The Royal Academy has just given a clutch of architects license to fool around with the space in its lofty galleries in an exhibition called Sensing Spaces. It’s not hard, with false walls and ceilings, mazes and mirrors, to produce confusion and disorientation – and the pleasant sensation of discovering ‘places’ that are illusory. Or are they?

Only recently I was writing (‘Displaced’, January 27) about what constitutes a place; the Academy show elaborates on the question.What about gardens, though? Isn’t this exactly what gardens are for? I would like to arrange a show that does something similar in garden terms, experimenting with opening views and blocking them off, introducing masses (as summer growth does as trees come into leaf, and tall perennials fill a border) and withdrawing them again. It would be fun to ape the process by inflating and deflating balloon models – at full scale, of course. Inflate a yew hedge to divide a space and see the effect, then try one with a completely different texture – the shine of camellias or laurel or the intricacy of bamboo. Or a brick wall.

I would try out pergolas and trellises, eye-catching statues, gazebos, benches and fountains (tricky, perhaps, with balloons). I would see what difference colour makes – with lights perhaps – turning, say, a white garden into a yellow or red one. How would we record the effect of each change on your mood, your engagement and curiosity? There will be a way, I’m sure, short of wiring up each visitor’s brain.

Indeed the whole thing could probably be done with designers’ software. But no, I want the full Academy experience – not forgetting garden scents and bursts of birdsong.