Touted as the largest Victorian-era glasshouse in the world, designed by the celebrated architect Decimus Burton, Temperate House first opened to the public in 1863. After a five-year, $75 million makeover, which involved installing 15,000 new panes of glass and redecorating its metal frame with over 5000 litres of paint (enough to cover four football pitches), it's once again the gleaming "jewel in the crown" of Kew Gardens, housing over 10000 plants from the world's so-called "Goldilocks" zones (basically frost-free climates that are never too hot or too cold).
Sir David Attenborough called it a "breathtakingly beautiful space" when unveiling it in early May, and it's hard to disagree, especially today, with the sun streaming through the roof during one of London's sporadic, mood-enhancing good weather weeks, when there are few more pleasant places to be than Kew, a UNESCO World Heritage site by the River Thames on London's bucolic western fringes.
Home to more than 30,000 different species of living plants - the most diverse collection on the planet - the gardens spread 132 hectares from Kew Palace, a one-time retreat of King George III, having initially blossomed in the late 1700s under the direction of the monarch's friend and confidant, Joseph Banks. A botanist on James Cook's first round-the-world voyage, Banks brought back eucalypts, acacias and banksias from New South Wales, as well as other exotic flora from the Americas, Asia and south Pacific.
Kew's Australian connections endure, with the director of horticulture here, Richard Barley, a Victorian, formerly of Melbourne's Royal Botanic Gardens. And one of Kew's most notable 21st century additions, planted by that man Attenborough in 2005, is a Wollemi pine that was believed extinct but discovered in the bush near Sydney in 1994.
We browse several endangered plants in Temperate House, whose soothing atmosphere is enhanced by its trickling water features. Especially alluring is the Encephalartos woodii, a type of cycad from South Africa that resembles a palm and has been dubbed "the loneliest plant in the world". Only male specimens now exist - finding a female has proved to be one of modern botany's biggest challenges.
You could spend all day exploring Kew - and you could come in every season and have a totally different experience, helped by a wide-ranging programme of botanical events and workshops sure to delight green-fingered souls. We're here when the bluebells, wisteria, tulips and magnolia are in full spring bloom and birdsong fills the sweet-scented air. We previously came in early autumn, when the foliage on the gardens' tree-lined avenues and woodlands were tinged with golden, fiery colours.
In winter, especially around Christmas, Kew has a festive feel with illuminations and mulled wine aplenty, and, occasionally - such as when the polar-like "Beast from the East" arrived in March - everything is rather magically carpeted in snow. It's during such cold snaps that you'll really appreciate Palm House, another Decimus Burton-designed glasshouse that's heated like a steamy rainforest and teems with luxuriant vegetation from the tropics. Summer (June-September) at Kew is prime picnic and al fresco concert season, with families and couples congregating on the lawns, by the resplendent roses, and in the dappled shade, sipping Pimms, gin and tonics and fruity ciders and revelling in the Arcadian vibe.
Although you'll find a map is handy to navigate the gardens - you're given one with your entry ticket - it's lovely to just wander (there are signposts in case you get really lost). Besides all the eye-catching flowers and trees, you'll pass cafes, eateries and food and drink pop-ups, Greco-Roman-esque temples and follies, a Chinese pagoda, a Japanese minka and a rustic cottage once belonging to Queen Charlotte, the wife of George III and an amateur botanist who helped expand the gardens.
There are pleasant surprises, too. Next to a lily-layered pond, beneath the twisting branches of Chilean monkey puzzle trees, we see geese and adorably cute fluffy yellow goslings nibbling at the grass. Nearby, one of the resident peacocks struts and fans out his magnificent feathers, but the object of his courtship doesn't seem overly interested. Perhaps she's put off by the small crowd who've gathered, pointing smartphones and cameras.
Don't miss the "wobbling" Treetop Walkway. Ambling amid the canopies of oak, sweet chestnut and lime trees 18 metres above the ground, you'll feel like a kid again, while enjoying a bird's eye view of these enchanting gardens.
Admission to the Royal Botanic Gardens Kew - its official name - is priced from £16 ($29) for adults, £14 for concessions, and £4 for children aged 4-16. It's about a 30-minute Tube ride from Westminster, central London, to Kew Gardens station. See www.kew.org
Steve McKenna was a guest of Kew Gardens.