Open Garden Squares Weekend has just celebrated its tenth year with a record 174 gardens in London taking part, including convents, prisons, museums and churches. Most squares are usually closed to the public, although Kensington and Chelsea council is consulting residents to see whether they would allow greater public access. For only £7.50, you can visit as many gardens as you like in a weekend (opensquares.org ) - far cheaper than the RHS Chelsea Flower Show. Here are the top tips I gathered gallivanting around some of London's best-kept secret gardens:

1 It's hip to be square

“London is unique - no other city has as many squares,” says Drew Bennellick, head of partnerships at English Heritage. “The square as a design concept is timeless.” Whatever shape your garden is, you can make the space appear bigger by introducing a square, using edging or planting.

2 Follow your nose

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St Mary's Secret Garden is a community horticultural therapy garden near Old Street in Central London. Planting includes thyme and lavender. Grow fragrant herbs and flowers in raised beds or from hanging baskets so they are nearer your nose.

3 Keep it in proportion

Proportion is important, even in the smallest gardens. Whether you have a window sill or an acre, keep everything on the same scale. Big spaces demand big plants and vice versa. But, if you have only a very small space, consider one big gesture - try a potted olive tree underplanted with geraniums, for example.

4 Aim high

The Roof Gardens in Kensington is an exotic urban oasis six floors above the clothes shop Gap. “Despite the wind we grow jasmine and wistaria,” says David Lewis, its head gardener. “The top soil is only 18in deep but we mulch regularly to keep it fertile.” This is true for any garden but especially so for one so exposed to the elements. Just don't overload your roof.

5 Box clever

Dead box hedges don't drop their brown leaves so just spray them green and no one will know the difference. Warning: don't try to correct patchy growth this way because you will kill the plant.

6 Look East

Cable Street Community Gardens in East London has 45 plots and gardeners from nearly as many countries. Among the exotic plants they grow is ginger. “You can grow ginger from even the gnarliest root,” says Jane Sill, the co-ordinator of the gardens. “Put it in a pot with fairly gritty soil and don't over-water. You will get glorious lily-like flowers.”

7 Reduce, reuse, recycle

“You don't need to buy fancy equipment,” Sill says. Cable Street is full of cobbled-together bits and pieces that somehow do the job. “Cut the bottoms off old plastic bottles to make cloches, use bamboo cuttings to stake sunflowers and plant seedlings in toilet roll tubes.”

8 Tackle ailing railings

“A garden is incomplete without railings,” Bennellick says. They cost a fortune to replace, especially if they are listed. Restoration is relatively cheap and easy: chip the rust away, scrub with a steel brush, brush off dirt and dust, undercoat twice with anti-rust primer and then apply two coats of black outdoor paint. Washing down with white vinegar annually reduces rust.

9 Get the perfect lawn...

“There is a secret to those stripes,” Bennelick says. Here it is: use an old-fashioned cylinder mower. Walk slowly, cutting around the perimeter first to provide a turning area. To perfect the stripes (and get a workout) go over with a roller.

10..then sit back and enjoy

No garden party would be complete without a glass of Pimm's. The residents of Edwardes Square in Kensington enjoy the finest blend. Their secret? Peel the cucumber and add borage flowers.

Explore Gardens

• Hampton Court Palace Flower Show

• Chelsea Flower Show

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