This garden experiment could help you remember your passwords

According to New Scientist, stimulating your sense of smell with different perfumes not only improves your mental performance, but also slows down and reverses some signs of cognitive decline.

A small trial of adults aged 60 to 85 showed that a device that puffed out 40 different scents during nightly sleep improved verbal memory by more than 200 per cent.

200 per cent! I rejoiced. Our garden has at least 40 scents, including "mating wombat". I'd not only be able to remember everyone's birthday, but all my passwords, just by keeping my bedroom window open at night!

Then came the reality check. I remembered that 200 per cent does not mean 200 times better but "twice" (I need to eat more chocolate-covered walnuts). Nor was the study named. How small is a "small trial"?

On the other hand, a large body of work already connects various scents with improved memory, especially rosemary. And I love scents, not just the floral and foliage kind, but the perfume of freshly baked choc-chip biscuits, bread, or the whole bulbs of fresh roasted garlic. From long practise I can tell when biscuits, cakes or vegie fritters are cooked as soon as the first whiff sneaks out of the oven.

Increasing the number of perfumes in your garden, and making sure you get regular doses of their scents, is an experiment with absolutely no downside, apart from possible allergies, or being stung by a bee.

The easiest way to get a long dose of scents is when you're asleep. Sadly most plant scents are strongest during the day, as warmth evaporates their essential oils. A few have evolved to generously perfume the air after dark. Night-blooming jasmine, Cestrum nocturnum, is the wow! of night-scented plants. It's a hardy yellow-flowered bush, growing up to four metres, with a powerful vanilla-almond scent that perfumes your entire garden all through spring to autumn. It also repels mozzies as well as attracting moths and bats that eat mosquitoes. It's nickname is "Lady of the Night". I rather like the idea of having a Lady of the Night guarding our garden.

Sadly there are disadvantages to inviting The Lady of the Night to dwell by your bedroom. The first is that she will only tolerate down to minus 4 degrees. This is easily solved: grow her in a pot for a sunny patio or courtyard, or take her inside for a few months by a lighted window in winter. This will also keep the plant smaller, and lessen the intensity of the perfume. Few gardens need a four-metre bush full of scent.

The second problem is that 'The Lady of the Night' can become a weed, but given our winter frosts, that's unlikely unless you move far north. The third disadvantage is more serious: a few people find the scent can trigger asthma, headaches, sinus and similar symptoms. This is yet another reason to only grow The Lady of the Night in a pot, where it can be removed if vulnerable visitors arrive.

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A safer and more lovely choice for evening perfume all through spring and summer, though not nearly as powerful, are night-scented stocks. These lovely little annuals bloom from early summer to late autumn, about six weeks after sowing. The flowers range from white through every shade of pink, mauve and purple. The perfume is classic 'floral', soft but pervasive, released in the late afternoon to greet you as you come home, and lasting for a few hours after dawn.

Then there's a Mandevilla vine for a trellis, fence or pergola. It has a glorious garden fragrance in the daylight but is equally enchanting at night, with dazzling trumpet-shaped blooms in vibrant reds and pinks. Mandevilla accepts only mild frost, but grow superbly in Canberra courtyards or over the balcony.

Thankfully most deeply scented plants are usually fragrant at night too. If you plan well you can have stunning scents every month of the year.

January: Liliums, grown in dappled shade, a scent that fills a room or courtyard; basil and ripe tomatoes; freshly mown grass and the perfume of rain on hot soil or lawn.

February: Tuberoses, curry plant, more ripe tomatoes, English lavender, frangipani, gardenia.

March: English lavender, ginger lilies, masses of roses if you have remembered to prune and feed them, stocks, early hyacinths and heliotrope, that smells of just-cooked cherry pie with a touch of vanilla.

April: Sweet peas, climbing Chinese star jasmine, oriental lilies.

May: Native frangipani (Hymenosporum flavum), crowea, eriostemon or wax flowers, French and Italian lavender.

June: Daphne, scented camellias, winter sweet (Chimonanthus praecox).

July: Jonquils, brown boronia (Boronia megastigma) that also comes in yellow, reddish yellow or a rich mauve.

August: More jonquils, hyacinths, rosemary's foliage on a hot day, scented magnolias, various wattles, freesias, lemon and orange blossom, waratahs.

September: Star jasmine, lilac, more jonquils, lavender.

October: Wisteria's honey scent, sweet lily of the valley, sweet peas, early roses, mint bush (Prostanthera).

November: Roses, roses, roses, port wine magnolia, which is really a Michelia, its flowers so insignificant but so delicious you'll hunt for an hour till you find them blooming in a shady spot, gardenia, plus the fragrance of ripe apricots.

December: English lavender (dry you underwear on the lavender bushes for scented whiffs throughout the day), prickly bursaria, (small birds love to nest in it) and more lilies, so intense you only need a few to perfume your garden or house.

With luck you can also 'borrow' the scent from your neighbours' gardens to add to your 'perfumes to sniff 'collection, or make 'pretend' pot pourri - dried rose petals, lavender, and strawflowers with a few drops of scented oil every week or two. Try chilled rose petal or peppermint or lemon and ginger tea when you feel hot and hassled.

Nor do the perfumes have to be floral: the scent of baking choc-chip biscuits lingers in curtains and upholstery for days. Add the scents of toothpaste, dog food and dog farts (odours train the brain as well a scents). Go for a walk among the lemon-scented gums by the lake, or smell the grass after it rains on a hot day, or a fresh mown lawn...

There are thousands of scents to find, once you are out of an air-conditioned office. Try simultaneous brain boosters: take a walk amongst greenery and flowers while thinking creatively, like designing a bird bath or composing an ode to a magpie. Munch on chocolate-dipped walnuts, then sing an aria by Puccini - learning a new language boosts brain resilience too. In just six weeks you might even remember your passwords.