(NYTIMES)- If you have received a bouquet from that special someone this Valentine's Day, you may be looking for ways to extend the romantic gesture as long as possible.

Just like hangover cures, there are many theories about the best method for keeping flowers fresh. I wanted to find out if one method reigned above all. So I asked some flower experts and tried my own (not very scientific) homegrown experiment.

To start, I bought nine stalks of chrysanthemums from a grocery store and put each stalk in a clean glass bottle with about 12 ounces (354ml) of warm water and the following common treatments:

- Water alone

- Water and putting flowers in a refrigerator every night

- Sprite (1/4 cup) and water

- Vinegar (1 Tbsp), sugar (1 Tbsp.) and water

- Vodka (1/8tsp), sugar (1 tsp) and water

- Aspirin (1 crushed) and water

- Penny, sugar (1 tsp) and water

- Bleach (2 drops), sugar (1 tsp.) and water

- Flower food (1/2 packet) and water

There is some science behind these methods. But a word of caution before you try one: That little packet of flower food that came with the flowers may be your best bet. It likely has the right blend of antibacterial agents, a sugar source for food and an acidifier that will extend the life of your arrangement.

"The problem with home remedies is it's difficult to get the proportions right - put in too much bleach, and you might kill your flowers," said Dr Mary Hockenberry Meyer, a professor of horticulture at the University of Minnesota.

But if you did not get one of those packets - or if you are harvesting flowers straight from the garden - here are some things you should know.

Preparing your flowers for a long life

Let us rewind first, to the moment you receive a fresh bouquet. Before you even put your flowers in water, there are a couple of things you should do.

If you are using an old vase, wash it thoroughly because "whatever's left over from your last batch of flowers has a lot of bacteria in it," said Dr Chris Wien, a professor emeritus of horticulture at Cornell University. Those bacteria block water flow in the flowers' stems, causing your blooms to wilt sooner.

Right away, cut off 1.2cms to 2.5cms of the stems at a diagonal, using sharp scissors or a knife. Make sure to cut "in a tub or under running water, which prevents air bubbles from getting into the stems and blocking the flow of water," said Dr Amy Jo Detweiler, an associate professor of horticulture at Oregon State University. Remove any leaves or florets that would sit in the water, because those will cause bacterial buildup.

A little tender loving care

Ideally, you should first put your flowers in water around 43 degrees Celsius (and your additives, of choice), and then keep the vase in a cool place for at least a couple of hours. This process, called "hardening" or "conditioning," helps because warm water molecules move up the stems more quickly, while a cool environment minimises water loss through the flowers' petals and leaves.

Though you might intuitively want to place flowers by a window, direct sunlight can actually stress cut flowers more than helping them - remember, your blossoms are not really photosynthesising anymore so they do not need sun to make food. Normal indoor lighting works just fine.

Change the water at least once a week, recutting the stems and adding more preservative or food each time.

What didn't work

In total, I kept my flowers for 10 days. Every day I randomly shuffled the flowers around, to ensure that positioning would not explain the outcomes. On Day 5, I fully replaced the water and treatments for each vase.

So how did my treatments fare? In theory, soda, vinegar and aspirin should acidify the water so it more closely resembles the sap inside plant cells, helping the flowers take up fluid more easily. Vodka is thought to inhibit the production of ethylene, a gaseous hormone that causes flowers to mature and fruits to ripen. Copper, bleach and vinegar are antibacterial, and refrigerating should slow water loss and the breakdown of tissues.

By far, the worst performers were aspirin and vinegar with added sugar. Flowers in the aspirin solution started wilting just four days in, while flowers in vinegar and sugar started wilting on Day 6.

The aspirin treatment likely failed because it lacked sugar, and the vinegar treatment may have contained too much acid, said Dr Neil Anderson, a professor of horticulture at the University of Minnesota.

"For the water volume you used, you'd maybe want a teaspoon of vinegar at most." Though the flowers in the Sprite treatment stayed healthy, the solution had spots of fungus on its surface, which was not surprising because it contained a lot of sugar but no antibacterial ingredients.

The flowers in the penny solution also looked good, though the water appeared slightly cloudy, likely because the copper didn't dissolve enough to provide any antimicrobial effects. "It's a great psychological remedy, perhaps," said Dr Wien.

What worked

While the bouquets in aspirin and vinegar sagged, all the other flowers appeared robust, even in plain water. That may show the best way to ensure your blooms last longer: Get a resilient flower. Without realising it, I had chosen one of the hardiest flowers for my experiment.

This kind of chrysanthemum will probably live at least two weeks in the vase, and "you will not see a difference in any treatment," Dr Meyer predicted when I talked to her on Day 5 of my experiment.

Because of genetic differences, certain flowers - like chrysanthemums and carnations - simply last longer than others, Dr Anderson said. Though roses are a favourite for Valentine's Day, they usually do not last longer than a week, he added, a bit shorter than many other flowers. "Their petals aren't as tough and waxy, so they lose a lot of water and wilt fast."

The End

Of course, even if you pull out all the stops, you will not be able to ward off the inevitable. Rest assured, the fate of your Valentine's Day love story likely has little to do with your flower-keeping abilities.