I wondered if I had unknowingly picked an NGS day to visit Marwood Hill, but Dr Smart brushed aside my first question with a smile, reassuring me that it was "always like this".
I had spent the morning eight miles away at Tapeley Park (a garden currently enjoying a brilliant renaissance), and was feeling horticulturally pretty replete. However, Tapeley's owner, Hector Christie, gave both Dr Smart and his garden such an enthusiastic testimonial that it seemed positively wrong-headed to duck out of the opportunity to pay a visit. He was right, too. I don't think I have ever been to a garden that has exceeded my expectations so much.
Dr Jimmy Smart MBE VMH is a sprightly octogenarian who even before his retirement from medicine in 1975 had become something of a legend in horticultural circles. I was soon to find out why. Almost the first two plants that caught my eye - a low evergreen mound of mint-scented Prostanthera cuneata smothered in pretty white flowers, and a clump of the lilyish Paradisea lusitanica - turned out to have been introduced to this country by Dr Smart. (It must have seemed as though I had researched his horticultural career pretty thoroughly, but I must confess it was sheer coincidence.)
As we rounded the head of the lake and started to climb the bank beyond, Dr Smart paused to introduce a pair of handsome Turkish rhododendrons, Rungernii, and remembered driving them home to Marwood 30 years earlier. "What, all the way from Turkey?" I gaped. "No", he grinned, evidently enjoying the impression he had made, "from Exbury".
Although the Smarts had been living at Marwood since 1949, the garden was begun during the early Sixties when they found themselves able to purchase the valley of rough pasture that lay across the road below their house. A stream trickled through the bottom of the valley, which was dammed twice in order to form two lakes.
And while the bones of the garden started to take shape, Dr Smart planted trees: trees and shrubs raised from seed collected on trips to Australia and the Americas, trees bought from specialist nurseries, trees given by friends and colleagues who had become interested in his collection of the rarer and more beautiful magnolias, eucalyptuses, birches, willows and conifers.
We all know that collectors' gardens can fall down on design, resulting in the horticultural equivalent of a stamp album. No danger of that here. Take the main collection of eucalyptus and birch, for example. These have been intermingled, forming their own sizeable grove on the hillside overlooking the lake. The smooth, slim trunks of the gum trees, with their peeling bark and airy foliage, mix their stripy and dappled shadows with the pencil- thin, white birches. And Dr Smart takes care to see that the birch trunks are white: each winter they are washed as high as their slender, swaying crowns will allow.
Thirty years on, this part of the garden is still in the process of maturing, and it is obvious that, where space allows, Dr Smart is still adding to his collection. The 20 acres are as densely packed as the flowers on his Cornus kousa chinensis, and as Dr Smart says of these abundant blooms, "You couldn't stick a pin between them."
The wide and tranquil expanse of the lakes, however, preserves the garden from any sense of hectic overcrowding. The margins, though, are packed with orange and yellow giant primulas, intricately veined purple and white irises, arum lilies and astibes, of which Dr Smart has the National Collection. (It comes as no surprise to learn that he also has the National Collections of Iris ensala and tulbaghias, too).
Just as the success of the birch and eucalyptus grove turns on the play of light and shadow between the tree trunks, so the clumps of bamboo by the lake have been thinned dramatically to allow each cane to be seen in isolation - rather than forming a dense, light-blocking screen. This technique is practised also at Great Dixter, and repays the effort enormously.
Returning up the steep slope towards the new house that the Smarts have built for themselves at the top of the garden, we stopped at the first patch of level ground I had seen since my arrival. The rose- and wisteria- covered pergola arching overhead and the rows of fat, colourful herbaceous borders here give more than a passing nod to Giverny; but I got the impression that Dr Smart's heart lies with trees on steep hillsides rather than the level world of lawns and borders.
"Well, it's much easier to garden on a slope," said (a clearly very fit) Dr Smart looking up into the pergola. "I couldn't bear to have a level garden." It's a good point: there are so many plants, trees included, that offer their best perspectives to the birds; a problem that cunning use of a sloping site (or pergola) can resolve.
No less than five gardeners, under the headship of Malcolm Pharoah, are employed at Marwood Hill, which for a garden in private ownership is pretty remarkable these days. A large nursery occupies the old walled garden, selling a huge range of plants - nearly all of which are propagated from the garden, which helps to offset the costs.
Marwood Hill is a fascinating, exhausting garden, which - much as it offers itself to simple enjoyment - needs lots and lots of time to be appreciated. It was a mistake to try to fit it in with Tapeley Park on the same day. I'll know better next time.
Marwood Hill Gardens (01271 42528) are open every day from dawn to dusk. The plant centre is open daily 11am-5pm. Admission (honesty box) adults pounds 2; OAP pounds 1.50; children under 12 freeReuse content