Night fever: As dusk falls, the character of a garden changes. Nocturnal activities abound, and magical aromas fill the air. Emma Townshend on the lure of the shadows

The days are rapidly lengthening and suddenly it's warm enough to sit outside until it gets dark. As the chatter of neighbourly lawnmowers grows quiet, the sky becomes ever deeper blue, and Venus begins to shine in its own quarter of the sky. In the poem 'A Summer Night'', WH Auden wrote about just this kind of evening: 'Out on the lawn I lie in bed, Vega conspicuous overhead''. Or, as my friend Kate says somewhat less poetically: 'It's one of those nights that's begging you to sit out with a bottle of wine and talk ramblingly about the future.''

For the location of Vega, you will have to consult a star book. But for the perfect summer's evening you will need the perfect evening garden. We spend very little time thinking about how our gardens might work at night, except to scrutinise ads for garden lighting. Yet even in west London a garden will be lit well enough by the full moon to cast deep shadows - much better for moths and hedgehogs, and more enchanting for human beings too.

The best nocturnal gardens are not those lined with expensive flex, but those designed to use the magical quality of the night-time. Gardens that come into their own at night are something quite special, and yet we are usually oblivious to our plots' after-dark activities. We pack away our tools after a day's garden work in tired anticipation of an evening on the sofa, not ready for a night's bat-watching.

In daytime hours, we want tidy borders and colour schemes. But if we desire Ralph Lauren order in the sunlight, we want something much more Missoni for night-time. Centrally, we need perfume, preferably wafting in long mysterious pulses. And gardens do smell better at night. This has to do with the moths and beetles that are the main pollinators of many fragrant flowers. Moths avoid predators by being nocturnal, so many plants only bother to put out their signature scent once dusk is falling. Some flowers open exclusively at night - and they get a delightful specialist Latin term, vespertine (previously only known to me as the title of a Bjork album) to describe their night-loving ways.

However, you definitely don't need to buy truly exotic plants to get an exotically fragrant set of scents. Don't neglect the obvious: jasmine and honeysuckle will both produce the most extraordinary perfume and you can obtain pungent examples of either in any local garden centre and most DIY shops. Jasmine will do better in a container because honeysuckle tends to get infested with greenfly if it's not kept well watered. But if you buy the most ridiculously oversized pot your local B&Q has to offer, you will give these climbers a good chance of producing their gorgeous flowers for months on end.

Another sophisticated scent available from the most ordinary retail park is Nicotiana which you can buy at the moment in bedding packs. Nicotiana is the tobacco family (hence the Latin name) and you will need deep, rich soil for them, to mimic that of Old Virginia. Don't buy the stylish lime-green ones, as they lack perfume - aim for the whites if possible, such as Nicotiana sylvestris, growing to about four or five foot by the end of the summer.

And then there's Sweet Rocket and Night Scented Stock which you seed straight into your flowerbeds. Do as Vita Sackville-West described: 'I have just sewn half an ounce of the seed all along the pathway at the foot of a yew hedge, and now look forward to some warm evening when the pale barn owl is ranging over the orchard and the strong scent of the little stock surprises me as I go.''

I started to long for a fragrant night garden after reading Rosemary Verey's The Scented Garden. She has a whole chapter on terraces and twilight, from which my favourite piece of advice is that 'lilies grown in pots and tubs will lend an air of distinction to your terrace garden.'' An air of distinction - just what's always been missing from my outdoor patch. She is right though. She advises a series of lilies for flowers and scent all summer - beginning with the Asiatic hybrids in May then L candidum and L longiflorum, then in high summer the jaw-dropping Lilium regale, a four-foot tower of white blooms.

But what if you want something properly exotic? There are the Daturas and Brugmansias, the Angels' Trumpets, carrying with them the exotic taint of association with hallucinogenic drugs. Datura stramonium is known in the States as the Jimson Weed, and featured as a murder weapon recently on CSI. And here we really begin to meet the high-class, grown-up, Missoni end-of-night gardening, because you shouldn't even begin to think about growing these if you have small children as they are highly poisonous. Datura suaveolens, arborea and sanguinea are all to be recommended, for the long blooms heavy with fragrance.

Most exciting to me, I found reference in a wonderful book called The Evening Garden by Peter Loewer (Timber Press, £12.99) to the possibility of growing tuberose, which produces the strongest, most wildly oriental perfume there is, and forms the basis of many exclusive scents sold in Harvey Nichols. I had always thought tuberose came only from India. But this was one of those stupid mental blocks - I have many tropical gingers growing in my garden, so why shouldn't I try the tuberose (Polianthes tuberosa) which comes originally from Mexico, it turns out. Loewer quotes William Robinson, the eminent Victorian gardener, who said that tuberose often lived through London winters. But Loewer has also given me a new night flower to chase. To honour the full moon, I want the Moonflower aka Ipomea alba, a convolvulus with seven-inch flowers. If you know where I can buy one, let me know.

If you do one thing...

Snap to it

Now we are in the age of the digital camera, there's no excuse not to record all your garden triumphs on a weekly, if not daily basis. Gardens change so quickly at this time of year and you can fall into the trap of thinking you'll get it all in a photograph at some perfect point in the future. No, no - seize the day and do it now. You'll thank yourself later when you have a good record of how everything looked, how much it all grew, and how much hard work you put in.