How a cut stem drinks, and why the first hour matters most

There is no pump

A cut stem has no heart and no roots, and nothing inside it is pushing water upwards. What moves the water is evaporation at the far end. Water leaving the leaves and petals as vapour pulls on the water still in the stem, and because water molecules cling to one another the whole column follows, up vessels no wider than a hair. A flower in a vase is a wick with a fan at the top of it.

That single fact explains almost everything that disappoints people about cut flowers. A column held together by tension is fragile, and if it breaks anywhere along its length the flower above the break is cut off from the water below however full the vase looks. Most bouquets that fail early are not thirsty. They are blocked, and a blocked stem standing in fresh water is in exactly the same position as a stem standing in nothing.

Three ways a stem blocks

There are three common blockages. They arrive at different speeds, they look identical from the outside, and they want different things from you.

• Air. The moment a stem leaves water, air is drawn into the open vessels and settles there as a bubble that returning water cannot push out. This is why a stem that sat on the worktop while you hunted for the scissors drinks badly afterwards, and why the remedy is a fresh cut rather than a longer drink.
• Bacteria. Within a day or two the cut surface and the water around it are colonised, and the bacterial cells and the slime they secrete plug the vessels physically. Anything organic in the water feeds them, which is why one leaf left below the waterline does more harm than a week of general neglect.
• The plant itself. A wound in a stem provokes the response a wound in a branch does, and the tissue seals over with gums and with air-filled cells. It is a sensible thing for a plant to do and a nuisance for whoever wants the flower to last, and it is the reason a fresh cut works at all: you are not sharpening the stem, you are removing the part that has already closed.

Why the cut is angled

The angled cut is the one piece of flower advice everybody has heard and almost nobody has been given a reason for. The usual explanation is that a flat cut can sit flush on the base of the vase and seal itself against the glass, and that is true as far as it goes. A cut at roughly 45 degrees cannot lie flat, and it opens a longer ellipse of vessels than a straight cut across the same stem.

The better reason is timing rather than geometry. Cutting is not maintenance; it is the removal of the blocked centimetre at the bottom of the stem, and the new surface begins to seal and to gather bacteria from the moment it is made. So the angle matters far less than the gap between the cut and the water. Cut under a running tap, or cut with the filled vase standing at your elbow, and the angle looks after itself.

Use something sharp, and use it once. Scissors that crush rather than slice leave a mash of collapsed cells across the end of the stem, and a collapsed vessel carries no water however elegantly it was angled. A knife or a decent pair of florist's snips is worth more to a bouquet than anything you can add to the water.

The first hour

Almost all of the difference between a bouquet that lasts and one that does not is settled before the flowers have been in the room an hour. The order below is deliberate: water first, so that nothing stands about with a drying stem while you look for a vase.

• Fill the vase before you unwrap anything, and wash it out first if it has been standing in a cupboard. A vase that looks clean can still carry a film left by whatever was in it last.
• Strip every leaf that would fall below the waterline, and not one more than that. The leaves above the water are the engine pulling the column upwards, so stripping the stem bare out of tidiness slows the flower down.
• Take a finger's width off each stem at an angle and put it straight into the water, rather than laying the cut stems down in a row to be dealt with together.
• Give the flowers an hour somewhere cool and dim, in deep water, still bunched as they came. A stem that has drunk deeply is easier to arrange and far less likely to droop on the second day.
• Change the water every two days rather than topping it up, and take another centimetre off the stems while you have them out. Topping up dilutes the bacteria without removing any of them.

The flowers that want something else

The routine above covers most stems. A handful have habits worth knowing before you treat them like the rest, and in every case the habit follows from how that flower is built.

Tulips are the awkward ones. They carry on growing after they are cut, which no other common cut flower does to the same degree, and they lean towards whatever light is in the room. Cold water slows the growth, headroom in the vase accommodates it, and turning the vase each day stops the arrangement from bending into the window. A tulip that has curved overnight is doing what tulips do; it has about 6 days in it either way.

Hydrangeas take up water through their petals as well as their stems, which is unusual and extremely useful, because a head that has gone limp will often recover after a spray of water or a few minutes face down in a basin. They also want deep water immediately after any cut, deeper than you would give a rose. Gerberas want the opposite of depth: shallow water, because their hollow stems rot from the bottom upwards, and a scrupulously clean vase, because they suffer from bacteria in the water sooner than most. Irises are best bought closed, since they open indoors within a day and each bloom is brief, so an iris bought wide open has already spent the part you were paying for.