Flower food: what is in the sachet, and a recipe

The sachet taped to a bouquet costs a few cent and does more for the flowers than anything else you can add to the water. It is also the single most ignored item in Irish kitchens, usually because nobody has said what is in it.

Three jobs, one powder

Sugar. A cut stem has been severed from the plant that was feeding it. The buds still have to open, and opening takes energy. Sucrose in the water gives them something to run on, which is why food-treated flowers open more fully and hold their colour rather than going papery at the edges.

An acidifier. This is the part people never guess. Irish tap water is broadly alkaline, and water moves up a stem more freely when it is slightly acidic, somewhere near pH 3.5. Citric acid in the sachet brings it there. The effect is mechanical rather than nutritional: acidified water simply travels better through the vessels.

A biocide. Usually a small dose of something chlorine-based or a quaternary compound. Its job is to stop the bacteria in the vase colonising the cut end and blocking it. This part is doing the heavy lifting, and it is the reason a sachet beats every kitchen remedy.

The three are balanced against each other. Sugar without biocide is bacterial feed. Biocide without sugar keeps the water clear but leaves tight buds that never open. Neither works properly in alkaline water.

The dose is the point

A sachet states the volume it is mixed for: commonly half a litre, sometimes a litre. That number is not a suggestion.

Under-dosing is the common error. One sachet emptied into a two litre vase gives the bacteria their full ration of sugar and gives you half the biocide to control them. The water clouds faster than it would have with no additive at all, which is why some people conclude flower food does not work. It did what it was told to do with the water it was given.

Over-dosing is rarer and less harmful, but a double dose of acidifier will scorch soft stems. Anemones, ranunculus and sweet pea are the ones that show it first, with a brown collar just above the waterline.

Mix the food into the water before the stems go in, and stir until the powder has gone. A drift of undissolved granules on the base of the vase is not treating anything.

The homemade version, with the real ratios

If you have no sachet, this is the mix that works. Per one litre of cool water:

• 1 teaspoon of sugar. Ordinary white sugar. Not more.
• 1 teaspoon of white vinegar, or the juice of a quarter lemon. This is the acidifier.
• 1/4 teaspoon of household bleach. Plain unscented bleach, not a thick gel or anything with added detergent.

Measure all three. The recipe fails in exactly one way, and it is always the same way: people put in the sugar because it feels like food, skip the bleach because it feels wrong to put bleach near flowers, and end up with a warm sugar solution that clouds by day two.

Two substitutions that hold up. Lemon juice for the vinegar is fine and smells better. A clear lemonade can replace the sugar and the acid together if you use roughly one part lemonade to nine parts water, but you still need the bleach, and you are guessing at a sugar concentration that the sachet has already worked out.

Two that do not hold up. Aspirin is a very weak acidifier and no kind of biocide. A copper coin releases far too little copper into a vase to matter, and euro one and two cent coins are copper-plated steel in any case.

When plain water is the better call

Plain clean water beats a badly mixed homemade attempt, every time. If you are not going to measure, do not improvise.

The plain water routine that works: a properly scrubbed vase, cool tap water, complete water change every second day rather than a top-up, and a centimetre off each stem at every change. That is more effort than a sachet and it gets you most of the way there.

Plain water is also the right answer in a few specific cases.

• Daffodils and narcissi. They do not want the sugar, and their sap clouds the water regardless. Plain water, changed daily.
• Woody branches and blossom. Sugar does very little for them and encourages slime around the cut. Deep plain water, re-cut often.
• Anything in a vase a small child or an animal can reach. A vase dosed with bleach and sugar is not something you want knocked over onto a floor a toddler is crawling across. Plain water and a strict changing routine is the sensible substitute.
• Flowers going into floral foam. The foam is soaked in food-treated water once, at the start. Adding more to the top-up water does nothing.

Getting more sachets

Most Irish florists will hand you a few spare sachets if you ask when you are buying, and supermarket bunches often carry one taped to the sleeve that gets thrown out with the packaging. Keep them in a drawer. A second sachet at the first water change is worth more than the first one was, because by then the bacteria have had two days.

For the rest of the routine that surrounds all of this, see the full care routine. For what to do when a bunch is already drooping, start with triage by cause.