Cut flowers and making them last

Cut flowers die from bacterial blockage of the stems more often than from anything else, which is why the practices that extend their life are mostly about cleanliness.

What actually kills them

A cut stem draws water up through vessels that are easily blocked.

Bacteria multiplying in the vase water block them, which is why flowers wilt while standing in water.

Air drawn into the stem at cutting also blocks them, which is why recutting under water helps.

And the flower continues to respire and require energy, which is what flower food supplies.

The practices that work

A scrupulously clean vase. The single most effective measure.

Washing with detergent and rinsing thoroughly, since residue from previous flowers is a bacterial source.

Recut the stems at an angle with a sharp knife or secateurs, removing two or three centimetres.

Scissors crush the stem; a knife cuts cleanly.

Cutting under water prevents air entering.

Remove all foliage below the water line, which otherwise rots and accelerates bacterial growth.

This is the most commonly skipped step and one of the most important.

Use flower food at the stated dilution, which contains sugar for energy, an acidifier to improve water uptake and a biocide.

Home substitutes circulate widely and work less well than the commercial product, which is inexpensive.

Change the water every two days, recutting the stems each time.

Keep them cool and out of direct sun, away from radiators and away from draughts.

Keep them away from ripening fruit, which releases ethylene and accelerates senescence dramatically.

The stems that need different treatment

Where general advice fails.

Woody stems — lilac, hydrangea, roses in some cases — benefit from a split or a longer angled cut to increase the surface area.

The traditional advice to crush them is now generally discouraged, since crushed tissue promotes bacterial growth.

Bulb flowers — tulips, daffodils, hyacinths — prefer shallow water and cool conditions.

Daffodils exude a sap that is harmful to other flowers, which means conditioning them alone in water for several hours before combining, and not recutting them afterwards.

Hollow stems such as amaryllis and delphinium can be filled with water and plugged with cotton wool.

Stems that exude sap — euphorbia, poppies — benefit from searing the cut end briefly in boiling water or a flame, which stops the flow.

Euphorbia sap is an irritant and should not contact skin or eyes.

Arranging

A few principles that make an arrangement look considered.

Odd numbers of stems generally read better than even.

Varying heights rather than a flat dome.

A mixture of shapes: something with a large round head, something spiky, something small and filling, and something trailing over the edge.

Foliage as structure rather than as an afterthought.

And a vase whose opening is proportionate — roughly half to two-thirds the height of the arrangement is a workable guide.

Buying well

What to look for.

Buds just beginning to open rather than fully open, which have most of their life ahead.

Firm rather than soft stems, with no sliminess at the base.

Clean water in the bucket at the point of sale.

Foliage that is not yellowing.

And seasonal flowers, which are fresher, cheaper and generally have travelled less far.

The alternative

Worth mentioning.

Foliage and branches from a garden or a hedgerow last considerably longer than flowers and are free.

Dried and preserved material lasts indefinitely.

And a flowering plant in a pot generally provides more weeks of flower than a bunch, for a similar price.

Which flowers last and which do not

Worth knowing before buying.

Chrysanthemums, carnations, alstroemeria, lilies and many foliage stems last two weeks or more.

Tulips, anemones and ranunculus are shorter-lived and continue growing in the vase, which is why arrangements shift shape over a few days.

Roses vary enormously by variety and by how they were handled before sale, and a rose that droops within a day has generally been out of water at some point.

Poppies, hellebores and other stems that leak sap need searing or specific treatment.

And daffodils release a sap that shortens the life of everything else, which is why they should be conditioned alone in water for several hours before being mixed, if they are mixed at all.