And the gold goes to: Anna Pavord picks her favourites from the Chelsea Flower Show

Gold medals were scattered around the Chelsea Flower Show this year like petals falling from the apple blossom. In 2009, for instance, only three of the 13 show gardens got the top award. This year, 10 out of 15 did. And you can't suppose that this largesse was the result of a particularly good lunch on the judges' part. The panel meets at the cheerless hour of 8.30am on Monday, the day before the show officially opens.

In the Great Pavilion, where, for me, the heart of the show still lies, almost half of the plant nurseries also got gold medals. With grim skies, no sun, late frosts, this has been an appalling season for nurserymen. And yet, there were the exquisite delphiniums, the glowing peonies, the clematis clambering through trellis as though spring had provided every gift a grower could need.

The Blackmore & Langdon nursery, which exhibited at the first Chelsea show in 1913, this year won the President's award for their display of delphiniums. Their stand is a shrine, as far as I'm concerned. I approach it like an acolyte, with awe. For me, delphiniums exist in some parallel universe way beyond my capabilities. I adore them, but from afar. In the Great Pavilion they stood in unweathered perfection, neatly staked, in blues as various as a summer sky.

The nursery was set up in 1901 and John Langdon, grandson of one of the founders, remembers packing the precious spires to go to London by train in an old van with metal wheels. The coalman lent his horse to pull the van to the railway station at Bath. Another horse waited at Paddington to pull the van to Chelsea. Transport at least is less cumbersome now, but preparing the plants is still as time-consuming. Cotton wool round the buds, tissue paper round the stems. And twice as many plants to be prepared as will actually be needed. Just in case.

Of course, we, the public, see only the perfection of the finished thing. But on Avon Bulbs stand, the Sunday before the show, Alan Street was in despair about a particularly elegant iris he had hoped would be the star of his display. He had three pots of it, tall, narrow stems, grassy foliage, blue, delicately-veined flowers of exquisite poise and beauty. But not enough of them. Show rules dictate that in any clump at least half the flowers have to be in full bloom. And no amount of cossetting had persuaded the iris that it wanted to push on into an unseasonably chilly world. Avon Bulbs got a gold medal. Of course they did. But when I went to congratulate him, Alan was still mourning that iris.

The special Diamond Jubilee award in the Great Pavilion went to the Dutch firm, Warmenhoven, showing alliums and amaryllis. If you are thinking of planting alliums in your own garden, there is no better way to choose than seeing loads of them all together in the same place. Pictures on a website or in a catalogue don't tell you enough about the relative size of different varieties. And the differences in colour are subtle – far too subtle for digital imaging.

'Pinball Wizard' has monster heads, as much as 20cm/8in across on stems 60cm/2ft tall. But in a garden, it's often useful to have a taller allium, with a smaller head, which does not draw so much attention to itself. That's why I like 'Purple Sensation'.

Gold medals were glinting out of half the eight plots showing in the Artisan Garden category. Lined up along a leafy walk in Ranelagh Gardens, these small plots (on average 7m x 5m) benefit from their setting. It's green, it's relatively quiet. They feel real in a way that the show gardens on Main Avenue sometimes don't. The Ishihara Kazuyuki Design Laboratory took the prize for the best of this bunch and indeed, it was a beautifully put together plot: little hummocks of moss, rounded pebbles carefully kept wetted to show up the colours, an elegant enkianthus hanging in front of a traditional Japanese tatami room.

But my favourite here was a little garden, packed with marigolds, promoting the work of WaterAid. It recreated a scene we see all over Sikkim when we are travelling there: the thatched platform of a hut, with children's T-shirts hung out to dry under the eaves, a water tap decorated like a shrine with flowers and leaves, recycled tins planted with veg, recycled timber holding up beds of herbs and flowers, a mud-walled reservoir, capturing water from the bamboo gutters of the hut. Though carrying a serious message, this was a plot full of joy and delight. So thank you to the Herbert Smith Freehills foundation who fund WaterAid and to Patricia Thirion and Janet Honour who designed the garden. A triumph.