Gardening: God bless you, 'Chinese' Wilson: Anna Pavord contemplates her favourite hydrangeas and pays tribute to the stout fellow who brought them home to England from a mountainside in China

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THE PLANT hunter Ernest 'Chinese' Wilson set out on his third expedition to China at the end of 1906, with a party consisting, as he noted in his diary, of '18 carrying coolies and one head coolie, two chairs, two handymen, an escort of two soldiers, my Boy and self'. From this trip, he brought back the first regale lilies, though his entire consignment rotted on the sea journey home. They had been packed alongside raw animal hides, which did them no good at all.

Stoicism was the thing in those Boy's Own days, and Wilson's upper lip was so stiff he could scarcely speak. He could write, though, and his diaries provide the underpinning of Roy Briggs's new study of the man and his travels, 'Chinese' Wilson (HMSO, pounds 19.95).

This third trip, funded by the Arnold Arboretum in the United Staes, produced Lonicera nitida, Cardiocrinum, and the brilliant blue Ceratostigma willmottianum, which is flowering now in the garden, as well as my favourite hydrangea, H. sargentiana, which is named after Charles Sprague Sargent, the director of the Arnold Arboretum.

After reading about Wilson's travels, you look at such shrubs with new respect. I ordered my H. sargentiana 10 years ago from Hilliers nursery near Winchester, and it arrived, neatly wrapped, on a lorry. Wilson got his from the slopes of a mountain in western Hupeh. The weather was appalling, the terrain tough, accommodation even tougher. 'Dingy and damp', he writes of a Buddhist temple where they found shelter one night; and, 'a wretched hovel', of the charcoal- burner's hut into which he and his party crept the following day. Two other nights they spent in a piggery.

All one can say is 'thank you'. H. sargentiana has been overtaken now by H. villosa, but at the beginning of the month it was the best thing in the garden, with huge, paddle-shaped leaves the texture of sharkskin. The flowerheads are flat, about a foot across, filled in the middle with tiny mauve flowers. Each has bright blue stamens. Haphazardly arranged around the edge are the sterile florets, quite a stark white, tinged with mauve.

These great flowerheads are held on stiff, hairy stems, and the whole bush has a rigid, formal look. It needs space. And, to look its best, it also needs fairly deep shade. Mine grows under the shade of an old Portugal laurel. This kind of overhanging shade may draw the shrub up more than if it were growing in the shade cast by a building, but for the moment it seems happy.

It is no good trying to cram a hydrangea such as this into a dust scrape. It needs rich, well- fed ground, and blankets of mulch each year to keep the soil moist and cool around its roots. Hydrangea villosa, the present star in the garden, needs similar conditions, though it is not so fussy about being in shade. This stands higher than H. sargentiana, though some of the once- upright growths on my specimen are now leaning on their elbows, peering out from a ground cover of ginger mint and hostas. The leaves are long, narrow, hairy, softer in texture than H. sargentiana. The flowerheads are deeper in colour, though made up the same way with a big central mass of tiny flowers, surrounded by a showier ring of sterile florets. The overall effect is deep mauve, though when you look into the flower, you see there is a great deal of blue.

To get the best from hydrangeas, you need to spend time preparing their quarters, enriching the soil with manure or compost if necessary before planting. Chemical food is no substitute. Only hydrangeas forced to live in the more cramped conditions of a tub need this kind of artificial boost. Although by nature they are woodland plants, growing in dappled shade, they do remarkably well in tubs in full sun. In this situation, the showier mopheads look more at home than the delicate lacecaps.

Neither H. sargentiana nor H. villosa would give of its best in a tub. They grow too big. They are insufficiently domesticated. Grow them in a shady corner of the garden with Japanese anemones for company. These are excellent plants that never need spraying or staking or fussing over, and they come at just the right time for the hydrangeas. White varieties, such as the old 'Honorine Jobert' raised in the 1850s, shine out more in shade, but the common silvery pink types give a more subtle combination of colours. The anemones will cope with quite deep shade, although they do not flower there as freely as they do in sun.

So far, I have been disappointed by Hydrangea quercifolia. It has a lot to live up to, being in the same border as H. villosa and H. sargentiana, but its habit is lax and stooped and the leaves, though an interesting shape, seem to weather badly. The flowers are cream and droop down in rather shapeless long panicles. The way the other two hold their flowerheads is so much better. They present them like waiters swirling into a dining-room with plates poised high on their fingertips.

Had the soil been a little more acid, I would have gone for Hydrangea paniculata instead, perhaps the cultivar 'Kyushu', which I saw looking good in a woodland garden earlier this summer in company with the blue flowers of a hibiscus. This has wonderful glossy leaves and huge pyramids of cream flowers. Some forms can get up to about 12ft, but Kyushu is generally more compact.

Unfortunately, it would not be happy in my garden, but it is a shrub I would like to grow. I might try clouds of blue willow gentians around its feet. I have not succeeded with those either, though they are said, unlike most of their family, not to be fussy about soil.

Although they are widely planted, the mophead hydrangeas, such as H. paniculata, seem to be happiest in soil that is on the acid side of neutral. It is well known that on limey soils, mophead hydrangea flowers are pink, rather than blue. That does not matter, but limey soils often make the hydrangea leaves horribly chlorotic as well. The combination of yellow foliage with the pink flowers is not a pretty one. A dose of chelated iron helps improve the condition, but it is so much easier to garden with, rather than against, prevailing conditions and to throw away the medical props.

The first hydrangea I ever had charge of was a large pink mophead that grew outside the gate of our cottage in West Sussex. Following the edict of a neighbour who came patrolling regularly down the lane to see what I was up to, I cut the whole thing down to the base every autumn. It takes a new gardener, as I was then, years to shake off basic misapprehensions such as this. I wondered for several years why I got strong growth but never any flowers.

A book gave me the answer. 'Time to cut that hydrangea down,' shouted my neighbour that year over the wall. 'I thought I'd leave it alone this year,' I answered as boldly as I dared. 'It won't flower,' he said with chilling finality as he stalked on down the lane. He evidently had not noticed that it had never flowered anyway.

So, do not cut your hydrangea to the ground every year. This is a good technique for rejuvenating old, overgrown hydrangeas, but most need only occasional thinning. Cut out two or three stems from the base of the plant, choosing growths that are lax or unproductively twiggy. This is a job that is best done in spring, when you take off the old flowerheads. These provide some protection against winter weather. They also look good when rimed with frost.