Gin blossoms: If you want to create a beautiful, flower-filled hanging basket, ask a publican

By way of consumer research, I asked a hard-drinking friend of mine if he knew of any pubs in his area with good flowers. "Flowers?" he said incredulously. "Flowers?" he repeated, his voice rising with disdain. "I don't go to pubs for bloody flowers".

His drinking patch evidently does not include the area round Kingston-upon-Thames where, at 93 Elm Rd, Janet Turnes and her husband Manuel keep The Wych Elm. This is a pub so dripping in flowers that even the most blinkered alcoholic must notice them as he stumbles towards his pint.

The Wych Elm is a domestic-looking Victorian pub, curiously marooned now in roads of suburban semis. It rises straight up from the pavement, the front almost entirely swathed in a waterfall of flowers. Erupting from a huge barrel of ivy and petunias, a hop vine climbs up twine towards the top of the inn sign. Window boxes bulge with purple petunias and blue felicia, with ivy-leaved geraniums pouring out on all sides. By the door, two enormous cannas, one purple, one green, loom out of a terracotta pot with a grey-leaved helichrysum wriggling out from under their vast leaves.

Pubs used to be rather proud of their gardens. At the Clock House in East Dulwich, for instance, Peter and Frances Key used to have an astonishing display with masses of flowers bubbling up from the wooden haycart that sat in the forecourt. Huge bushes of white daisies on four-foot stems packed the wooden half-barrels lined up along the fence.

I once asked Mr Key why he put on this extravagant display, "It's great for business", he said. The regulars loved it. It caught the eye, got punters through the door. People noticed the flowers when they went by on the bus. Then they came back to check out the place. "I can't understand why all pubs don't do it", he said. But they don't. And at The Clock House now, there's not even a wisp of petunia as a welcome.

So it's all the more heartening to come across The Wych Elm, with its extravagant hanging baskets and window boxes. f "She's mad" says Manuel Turnes, of his wife Janet. "She never stops." And with pub opening hours what they are, it does seem extraordinary that each year Janet Turnes manages to stage such an extraordinary show. "Oh sometimes I'm out here at two and three o'clock in the morning planting up tubs," she says, as though gardening after midnight is the most natural thing in the world.

"Here" is a corner in the big garden at the back of the pub, where she mixes her own compost and pots on her plants. For window boxes and hanging baskets she uses the dependable, long-flowering plants that all gardeners have learned to value: yellow bidens, petunias, geraniums in quantity, lobelia and the grey variegated trails of ground ivy (Nepeta hederacea 'Variegata').

I've picked up some good gardening tips from publicans. Peter Key used to grow his plants in Gro-bag compost, which he reckoned was the cheapest way to buy the stuff. He bought his plants wholesale at the Covent Garden market. Janet Turnes brings carloads back from Evergreen Wholesale Nursery in Banstead. In very hot weather, Mr Key used to give his hanging baskets a bucketful of ice each. It took at least two hours to melt, he said, keeping the compost cool and moist as it did so. The Turnes have invested in an automatic irrigation system. Key fed his containers several times a week with Phostrogen. Janet Turnes incorporates slow-release fertiliser when she mixes her compost and then feeds with Tomorite.

The best pub window-boxes are wooden, made to measure to fit the pub windows. One publican told me he painted the insides of his windowboxes with car underseal, which he found preserved them pretty well. They have to be strong, not to buckle under the weight of all the stuff that's packed into them. Janet Turnes says the key thing is to soak the plants really well before you plant them. "Then you can squish the rootballs really tightly into the space." She manages to get 28 plants into a basket just 40cm/16in across. And not just get them in, but keep them flowering the whole summer long.

At The Wych Elm, as Mr Turnes points out, they have to look after their regular customers. There's no passing trade, so it pays to make the place look nice. But the pub flowers are not just a business proposition. Janet Turnes is the kind of person who, marooned 40 floors up in a tower block, would still find some way to garden. She's passionate about it, so passionate that in 2011 she won a Gold Medal at the Hampton Court Flower Show for a garden she designed there.

You won't generally find busy lizzies in pub window-boxes or hanging baskets. They need too much water. But despite this, there used to be a phenomenal display of them at The Hillgate in Notting Hill, where publican Liam Murphy had at least 70 tubs, hanging baskets and window boxes round his pub. Mr Murphy grew the busy lizzies in two huge hanging balls at first-floor level.

"How many plants in each ball," he asked me once, with the air of a man nursing a happy secret. "Two dozen?" I ventured cautiously. "Two dozen be damned" he said. "Seventy. Seventy in each one."

At the back of The Wych Elm is a surprisingly large garden, with a pergola swathed in trachelospermum running down the right hand side. In winter the whole structure is covered in bubble wrap to make a protected shelter for the many tender, exotic plants that Janet Turnes grows in the back garden: cannas, bananas, huge brugmansias, tender salvias. Some of the big geraniums are overwintered in the bay window of the bar. "She's mad" says Manuel Turnes again, as his wife describes all the things she has to do to keep the pub garden blooming. But it's obvious he loves it too. "Sometimes, after midnight when the pub has shut, I sit out in the darkness for half an hour under the pergola. The smell of those flowers! It's so beautiful. So peaceful."

The garden at the Wych Elm, 93 Elm Rd, Kingston-upon-Thames KT2 6HT is open on 28 July (12noon-6pm), admission £3. Garden show judge Jim Buttress and Radio Kent's Jean Griffin will be on hand to answer gardening questions, and there'll be home-made teas.