Flower care: what actually extends vase life

Most cut flowers die of blocked plumbing, not thirst. A stem seals over within minutes of being cut, bacteria colonise the cut end within a day, and the head wilts above a vase that is still full. Almost everything worth doing for a bunch of flowers is about keeping that one narrow channel open.

There is a lot of folklore attached to this, some of it actively bad. What follows is what to do, in the order the effort pays off, and what to stop doing.

The five things that matter, in order

1. A clean vase. This is first because it is the one people skip and the one that costs nothing. A vase that has held flowers before carries a biofilm on the inside that a rinse will not shift. Wash it in hot water with washing-up liquid, scrub the base where the residue sits, rinse until the water runs clear. If a vase has a narrow neck and you cannot get a brush into it, a spoon of bleach and hot water left to stand for ten minutes, then rinsed twice, will do the job.

2. A fresh cut, made under water. Cut two to three centimetres off every stem at a slant, with the stem end under running water or in a bowl, and get it into the vase within seconds. The slant stops the stem sitting flat on the base of the vase; the water stops a plug of air being drawn up the stem as you cut. Use a sharp knife or floristry scissors. Household scissors crush the vessels they are meant to open, which is why a bunch cut with a blunt pair often stalls on day two.

3. Nothing green below the waterline. Strip every leaf that will sit in water. Submerged foliage rots within a day and turns the vase into a bacterial culture, which puts you straight back to problem one. Take the leaves off cleanly rather than tearing them down the stem.

4. The sachet. Use it, mixed at the ratio on the packet, in the volume of water the packet assumes. Flower food is three things at once: sugar to feed a bud that has been cut off its supply, an acidifier to drop the pH so water moves up the stem more freely, and a small amount of biocide to keep the water clear. Half a sachet in a full vase is worse than none, because you get the sugar without enough biocide to control what the sugar feeds. The full breakdown of what is in the sachet covers the homemade version and the ratios that actually work.

5. Where you put it. Cool, out of direct sun, away from the fruit bowl, away from radiators and off the television. Ripening fruit gives off ethylene, which is the signal that tells a flower to finish; a bowl of bananas beside a vase of carnations will shorten them by days. Heat speeds every process you are trying to slow down. In an Irish house in winter, the two worst spots are a single-glazed windowsill, where the bunch freezes overnight and cooks in the afternoon, and the shelf above a radiator.

The full routine sets all of this out step by step, including the water change cadence and the Irish house specifics.

Myths, and what to do instead

Aspirin. The idea is that salicylic acid acidifies the water. It does, very slightly. A crushed tablet in a litre of hard Irish tap water barely moves the pH, and it does nothing about bacteria. Instead: use the sachet, or a teaspoon of white vinegar and a teaspoon of sugar per litre if you have no sachet, which acidifies the water properly.

Lemonade or clear fizzy drinks. This one has a real mechanism behind it, which is why it will not die: lemonade is sugar plus citric acid, which is two thirds of a flower food. The problem is the concentration. People pour in a third of a glass, which is far more sugar than a stem can use, and there is no biocide at all. The vase goes cloudy by day two. Instead: if you are going to improvise, use a much smaller amount of sugar and add something antibacterial. A quarter teaspoon of household bleach per litre is the usual answer.

A copper coin in the vase. Copper is genuinely antibacterial, and the myth dates from when a penny was mostly copper. Euro one and two cent coins are copper-plated steel, and even a solid copper coin gives up far too little into a vase of water to matter. Instead: the biocide in flower food, or the bleach.

Hairspray on the petals. It coats them, which slows water loss and stiffens the flower for a few hours. It also seals the petal surface and marks anything pale. It has a place in wedding work on the morning of, and no place in a house. Instead: if a bunch has to look right for an evening, keep it somewhere cold until an hour beforehand.

The pattern is worth naming. Every myth on that list is a real mechanism applied at the wrong dose, or a real mechanism that flower food already delivers better.

What none of this can fix

Flowers have a ceiling, and it varies enormously by type. Sweet pea will give you four or five days no matter what you do, and carnations will give you a fortnight even if you neglect them. Judging a bunch against the wrong number is the most common reason people think they have done something wrong. The vase life reference table lists realistic days for fifteen common flowers, so you can tell a short-lived flower from a badly treated one.

Nor can care fix a bunch that was already old when you bought it. Cloudy water in the shop bucket, leaves yellowing at the base, and roses whose outer petals have been peeled off are all signs of stock that has been standing.

When a bunch does start to go over, some of it can be brought back and some cannot. Triage by cause tells you which you are dealing with, and includes the point at which the right call is to stop.

If a bunch has been good to you, the last thing to consider is not putting it out at all. Roses, hydrangeas, gypsophila and lavender all dry well, and a wedding or sympathy bouquet is usually worth the small amount of trouble it takes to keep it.