This weekend is when the city's finest garden squares, normally open to residents only, fling wide their gates for the Open Garden Squares Weekend. Thus you can enjoy the glorious azure-blue ceanothus at Eccleston Square, and savour the early flowering of many of its sumptuous roses, some collected in China and beyond by resident and rosarian Roger Phillips. You can also lounge on the perfectly manicured lawns of Eaton Square this Sunday, admiring sculptor David Harber's spectacular sundials.
Over in Islington, Arlington Square, used in the Second World War for trench shelters and barrage balloon moorings, now has more than 25,000 bulbs, plants and shrubs in its borders. Enjoy the fantastic planting, as well as The Gin Garden's aromatic concoctions, on Sunday afternoon.
Bayswater's garden jewel is Cleveland Square, surrounded by white stucco Grade II-listed houses and 150-year-old London plane trees. Nearby is three-acre Crescent Garden, which was recently awarded London's best large private garden square.
These elegant and historic garden squares, however, are just part of this great gardens show, organised by the London Parks & Gardens Trust in association with the National Trust, and founded by Londoner Caroline Aldiss 15 years ago when she felt the need to share her own home square, South Kensington's Collingham Gardens.
Now part of Chelsea Fringe, the Open Garden Squares Weekend embraces more than 200 diverse green spaces across 27 London boroughs, and these include award-winning allotments, secret courtyards, city farms, bee and butterfly havens, prison flower beds (accompanied tours only), floating flower gardens at Tower Bridge Moorings and even organic gardens springing out of a series of rubbish skips on the King's Cross development site.
Our increasing need to connect with nature has seen a sharp rise in the number of wildflower meadows in the city and suburbs, and many of these are on show this weekend. The newest is sky-high, where Kensington Roof Gardens head gardener David Lewis is enthralled by the emerging crop of clover, campion, yellow rattle and oxeye daisies; this is aside from the lake, woodland and resident quartet of pink flamingos. Visit on Sunday morning, and quiz him on how it's done.
Other open nature reserves include Camden's World Peace Garden, where former wasteland is now a woodland glade; the pretty Olden Community Garden, a wildlife haven not five minutes' walk from the Emirates Stadium; King Henry's Walk, in Islington, where you can learn how to harvest rainwater, and the Melissa Garden Bee Sanctuary, two minutes from Highbury & Islington Tube, as the bee flies.
You may have missed the chance to check out the veg patch at No 10 Downing Street, but you can get great ideas for edibles from St Quintin Avenue's Community Kitchen Garden, formerly a tennis court, where more than 100 locals grow a huge variety of global fruit, veg and flowers in 48 raised beds.
Monks ran a productive patch at the 12th-century Cistercian abbey in West Ham, so it makes sense that, surrounded by its ruins, locals have created an open-access harvest garden for flowers, fruit and veg. Saturday afternoon sees the Abbey Gardens annual vintage summer party and plant history tour.
If you're looking for planting inspiration, however, head for Covent Garden's best-kept secret — the award-winning Phoenix Garden, transformed, by keen volunteers, from a former car park into a wildlife haven of imaginative plants, including towering echiums and scarlet salvias, thriving within retaining walls of recycled newspaper and bomb rubble. That's upcycling, "up west" style.
One of the gardens we would never otherwise get to see is The Royal College of Physician's Medicinal Garden, Regent's Park. Here, you can take a tour to learn about the rare medicinal plants on show, including the Peruvian opiate coral tree, Erythrina crista-galli.
It might be safer, though, to sit under the plane tree that started life as a cutting taken from a seedling of the tree on the island of Cos, under which Hippocrates was reputed to have taught his students circa 350BC. The exalted Inner Temple Garden, normally open to the public only on weekdays, has existed since the 12th century and legend has it that the Wars of the Roses began after an encounter on the site.
There might be wars of a different kind on Sunday afternoon, because head gardener Andrea Brunsendorf, whose planting is nothing short of sensational, has organised a best-decorated cake competition as well as a dog show, with categories that include dog with the waggiest tail. What garden could possibly offer more?
Open Garden Squares Weekend: this Saturday and Sunday, June 8 and 9; weekend ticket £10 (advance)/£12, National Trust members £5 (advance)/ £6, under-12s go free: opensquares. org; facebook.com/London OGSW; Twitter: @Open Squares