Gardening: A good dunking beats gin and aspirin: You'll have jolly hollyhocks and perky agapanthus if you ignore old wives' tales and follow the latest advice, says Jillian Hamilton

Freshly cut flowers in a trug or wicker basket may look romantic, but would be better plunged immediately into a bucket of cold water. Days, even a week, can be added to their life by this means. And notice the word 'cut': to break even tender stalks with your fingers damages both stem and plant.

Common practices in flower arranging, such as bashing, splitting or shaving the stems, are also detrimental to cut flowers. And you can forget all you've been told about adding aspirin, gin, lemonade or a copper coin to vase water.

Dr Rod Jones, of the Victoria Department of Agriculture, with co-author Helen Moody, has published Caring for Cut Flowers. The book is the result of eight years of experiments in his Melbourne laboratory, with thousands of flowers from around the world, as well as on tests in the US, the Netherlands, Israel, and elsewhere in Australia.

According to Dr Jones, miracles of longevity are achieved by trimming flower stalks underwater at an angle. First, plunge hands, sharp secateurs, scissors or, ideally, a knife, and the stems into a sink or bowl filled with water. While all are submerged, cut about 2-3cm off the end of each stem.

This process is standard among some florists - especially with roses, gladioli, chrysanthemums and snapdragons. Its purpose is to prevent air bubbles being drawn up the xylem vessels, causing blockages and consequent withering.

Flowers that have been out of water for longer than 15 minutes, says Dr Jones, should again have their stems thrust quickly into water and be retrimmed.

Cut at a sharp angle to increase the area for water uptake. Ideally, the tip just touches the vase base, resembling the pointed toe of a ballet shoe during a pirouette. Squashing stem ends on the bottom of the vase inhibits water uptake, as does the compressing action of a blunt cutting instrument.

There are some flowers that are better not cut underwater. These include frangipani, dahlias, sunflowers, poppies, euphorbias and others that exude a milky sap or latex. These sometimes benefit from burning or searing. The stems can be held over a candle or gas burner until they are blackened, then put immediately into deep water. Alternatively, wrap flower heads loosely in cloth or tissue paper to protect them, then hold them in a bunch and dip the stems into 2cm of boiling water for a maximum of 20 seconds. Afterwards, place them immediately in deep water before arranging.

Flowers with woody stems, especially foliage plants, are thirsty and need deep water. Warm water may help to ease the flow up woody stems - though it can be death for some.

Nothing, though, will encourage hollow-stemmed flowers such as delphiniums, lupins and hollyhocks to take up water easily. Dr Jones suggests holding them upside-down, filling their stems with a standard water solution (see below), and plugging them with cotton wool or a piece of floral foam.

'Smashing woody stems, or splitting soft stems vertically, severely damages the water-conducting vessels,' he warns. 'The intention of breaking or hammering stems is to open up the structural wall of cells to allow rapid water absorption. But this only happens briefly. It wrecks cells, makes the plant prone to infections from bacteria and - worst of all - small bits of stem clog the xylem vessels.'

Overcrowding of vases is out. So is use of metal containers, since even silver or copper vases have metallic ions which curb the action of preservatives and decrease water uptake.

One traditional practice Dr Jones does recommend is the stripping of any foliage leaves that are submerged, since leaves are covered with bacteria and fungi that multiply in water. Do this with scissors to avoid tearing the plant. Water quality is also important. Dirty water clogs up stems, stopping the process of osmosis so the flower wilts and dies. 'Bent neck in roses is a classic result of plugging because of dirty water which might appear clean,' Dr Jones says. 'Microscopic bacteria and fungi are present even in the cleanest-looking water, buckets and work benches.'

Always scrub out buckets and wash down work surfaces with a weak solution of household bleach (not soap or detergent, as soap blocks flower stems). Add a dash of bleach to vase water. If the bleach contains 4 per cent chlorine, use 15 drops (about a quarter of a teaspoon) per litre of water. If the chlorine content is not stated, it means it is weak, so the dose needs to be as high as one teaspoon per litre. The vase solution still requires changing every second day.

The next advice sounds as if it comes from a Chinese restaurant: for many flower varieties, make sweet-and-sour water. That is, use sugar for food and vinegar for acidity. 'Never use sugar without also using germicide, and always include an acidifier, such as vinegar,' Dr Jones warns. 'There is nothing bacteria breed faster in than a nice sugar solution, so it must have inhibitors. The amount of sugar in the solution depends on the flower and whether it is to be used to give blooms a boost overnight in a bucket, or for everyday use.'

A standard daily solution for a litre of water is two teaspoons of sugar, one teaspoon of vinegar or a pinch of citric acid, and a quarter to one teaspoon of household bleach.

Vases should be topped up daily with sweet-and-sour water. Flower life is extended if the stems are retrimmed, underwater, each time vase water is changed.

No home-made solution or commercial preparation is suitable for all species. Tulips and Marguerite daisies both dislike sugar and need only chlorine and vinegar additives.

Fluoride, in most water supplies, reduces the life of many cut flowers. It causes a brownish discoloration, especially in the outer petals, and brown spots on petals, leaves and stems. Gerberas and gladioli are sensitive to fluoride injury, as are freesias, alstroemerias, tulips, snapdragons, chrysanthemums, Easter lilies, Asiatic lilies and certain roses. Freesias need rainwater or de-ionised/distilled tap water. They are apt to die within a few days in straight tap water.

It is difficult to extend the life of cut flowers in overheated rooms, or in direct sunlight, in draughts or near air-conditioning units. Cooler situations are always better. Flowers breathe and metabolise rapidly when it is hot, thus depleting their energy resources more quickly.

Even though people make it a rule to replace moisture vaporised in petals and blooms, misting is not approved by Dr Jones. It can cause fungal diseases and is recommended only in extreme conditions of heat or air-conditioning. If misting really is needed, it is usually the foliage that should be sprayed, not the flowers.

Most flowers, says Dr Jones, will last longer freestanding in water than in floral foam. But he accepts that foam has become an essential medium of the flower arranger's art. Foam should be floated on the top of a bowl filled with water and a preservative solution, and should not be used until it is soaked through. pushing the foam down into the water by hand creates an airlock in the centre.

Flowers destined for the foam should first be soaked for several hours in a deep container filled with preservative solution. Stems must be pushed deeply into the foam because it dries out from the top. If a stem needs to be repositioned, it should be taken out and re-inserted. Pulling stems back from the foam after insertion breaks contact between stem and foam, preventing water uptake.

Even when you have prepared your bouquet, arranged it in a generous vase, in an ideal solution, and set it somewhere cool, one danger still lurks. Flowers are destroyed by ethylene fumes, which are given off not only by car exhaust systems, ripening fruit, gas or kerosene heaters, and cigarette smoke, but also by the damaged heads and foliage of the flowers themselves.

Ethylene is a common gas with a sweetish, fruity taste and odour, often associated with the smell of apples, and it drastically reduces the vase life of sensitive varieties. Flowers that have lingered on city pavements, or even in markets in the summer, absorb it.

However, if ethylene-sensitive flowers - including agapanthus, anemones, carnations, cornflowers, delphiniums, freesias, gerberas, gladioli, Geraldton waxflower, orchids, phlox, roses, stocks, snapdragons, sweet peas, sweet Williams or waratah - are treated with silver thiosulpate (STS) when harvested, they should last longer. Florists should be able to tell you if the flowers have been so treated.

From the moment a flower is picked, it starts to die. Over the centuries, all sorts of people, from Madame de Pompadour to Constance Spry, have tried to find ways to slow the rate of death of floral arrangements, but no one has ever found a way to extend the life of a cut flower indefinitely. However, in their book, Dr Jones and Ms Moody offer a guide to 82 popular flowers, with detailed advice on how you can give them a fighting chance.

Caring for Cut Flowers by Rod Jones and Helen Moody, published by the Department of Agriculture, Victoria, Australia. Price: dollars 29.95 ( pounds 15). Telephone 010 613 651 7098. After March the book will also be distributed by Penguin in Australia.

(Photograph omitted)