That still leaves a bewilderingly large array to choose from, but Londoners short on space could limit the choice further by installing sculptures that are as functional as they are beautiful.
© Clive Nichols
A birdbath, when it is a perfect bronze dish with abstract birds perched on the rim — take a bow, sculptor Christopher Marvell — makes a fine addition, especially when given due importance on a wooden plinth. A fountain can make a beautiful sculptural centrepiece — prime example is Tom Leaper's bronze agave fountain at Tresco — but forgo the fol-de-rol varieties and try something sharper, such as Capital Garden Products' simple bowl fountain in fibreglass with eternally rippling water, for less than £500.
Sculptor Simon Allison's magical fountains feature bronze foliage cast from the real thing: water trickles from each leaf atop a tall stem. See the magic in action at Kiftsgate Court, Gloucestershire.
Pots can make wonderful sculptures, as well as fill an awkward gap where nothing will grow, but they need to be big, statement pieces such as Whichford Pottery's glorious Sassanian terracotta jars, 68cm high and richly embellished with squirls and squiggles.
Nobody sculpts better than Mother Nature. Consider the fantastic, perfect and diverse shapes of seed pods, magnified a hundredfold. Jim "The Blazing Blacksmith" Whitson's giant seed pod, nestled among plants, looks like a supernatural pumpkin.
Allium heads morph into Ruth Moilliet's shiny, stainless steel sculptures that look as if they might bowl about the garden, light as air. For a smaller space, you could buy a bunch of stainless steel 80cm allium wands from Mike Bigland, £65 each, and scatter those into the border.
Flowers and foliage make great subjects for coloured glass sculptures that glow when the sun shines through them; brother and sister Sarah and Dominic Hayhoe make luscious curtains of colour-streaked glass leaves, more like flat pebbles, while Neil Wilkin's glass fantasy flowers, spiky and vibrant, could rival any dahlia.
Rounded, organic shapes always work well in natural surroundings. Simulate the smooth spheres of box balls with similar-size spheres of layered zinc leaves from A Place In The Garden, or Moore Designs' giant balls of string made from rusted steel as well as polished stainless steel.
Tom Stogdon works with water-worn stones, layering them up like dry stone walls within huge discs set in steel frames with a central hole through which you can view the landscape beyond.
Sundials can make marvellous sculptures. Si Unwins' imaginative copper-topped column of giant seed pods made from ridged oak is just one example. David Harber's "light sorceresses" are sensational: verdigris copper figures beaten into shape and carrying a vertical sundial or mirrored light-reflecting disc. The sex and stance of the figure can be customised, but that's what you'd expect for a five-foot figure that costs more than £18,000.
However, you don't need serious cash to give your garden a dynamic piece of sculpture. Ammonites, those beautiful fossil swirls, suggest antiquity, but you can buy large, clever fakes in inexpensive reconstituted stone from Lucas Stone. You can inject colour into a border, and call it an installation, if you follow RHS Garden Wisley's lead and push an army of lavender-painted sticks into the soil to push up among grasses or ground-cover geraniums.
A handsome piece of driftwood or even a large stone, artfully placed, looks effective surrounded by a sweep of stipa grass. And a ubiquitous green man mask becomes intriguing if it is tucked behind a veil of ivy, or peering through a curtain of reed-thin verbena stems — proving that placement is every bit as important as the sculpture itself.
* Surrey Sculpture Society: Sixty-plus pieces from the Surrey Sculpture Society will be on show at RHS Garden Wisley's Sculpture Trail, which runs from August 24 to September 29. Visit rhs.org.uk
* The Sculpture Website has a large directory of sculptors working in diverse mediums, including many of those featured here. Visit thesculpturewebsite.co.uk
* Capital Garden Products: for fountains, plinths (capital-garden.com)
* Whichford Pottery: for decorative terracotta. See whichfordpottery.com
* A Place In the Garden: for zinc ornaments (aplaceinthegarden.co.uk)
* Lucas Stone: for reconstituted stone ammonites/statuary (lucasstone.co.uk)