Flowers to think twice about sending, and why

Most flower mistakes have nothing to do with taste. A flower carries a meaning, a chemistry or a smell the sender did not know about. Some of what follows is folklore that certain families hold dearly; one item can put a cat in a veterinary clinic. Knowing which is which lets you relax about the first and take the second seriously.

Count the stems for anyone raised in Russia or Eastern Europe

In Russia and much of Eastern Europe, an even number of flowers is what you lay on a grave. Bouquets for the living come in odd numbers. To someone who grew up with the custom, a bunch of ten carnations can land with some of the jolt of a wreath on the doorstep.

The trap is that the most familiar romantic bouquet in much of the world is the dozen. Twelve red roses is an even number, and so are the tidy bunches of six or ten sold at supermarket tills. When you order for someone with this background, ask the florist to make the count odd. Foliage and filler are rarely what anyone counts, but the main blooms should come to an odd number.

Some families relax the rule for very large bouquets, and many people do not mind at all. Since an odd count costs nothing, it is the easy default.

Chrysanthemums for a French or Italian friend

In much of the world the chrysanthemum is a cheerful, hard-working flower that fills autumn bouquets without anyone thinking twice. In France and Italy it is the flower of the cemetery. Around All Saints' Day on 1 November, when families traditionally visit and tidy graves, pots of chrysanthemums are everywhere, and that association colours the flower all year round.

So a French or Italian recipient may read a bunch of chrysanthemums, at least for a moment, as a message about death. White blooms make the link strongest; in much of Europe, white chrysanthemums are associated with mourning more generally. A single spray tucked among other flowers is less likely to register, but if you know the recipient keeps the association, leave them out.

That is a pity, because chrysanthemums typically last around 16 days in a vase. For similar stamina without the connotation, carnations manage around 14 days.

Lilies in a home with cats

This is the one item here that is not about manners. All parts of true lilies (Lilium) and daylilies (Hemerocallis) are toxic to cats, including the pollen and the water the stems have stood in. The mechanism is what makes lilies so dangerous: a cat does not have to eat the flower. Pollen brushes onto its fur as it walks past the vase, the cat grooms, and a tiny amount is swallowed. The toxin attacks the kidneys, and without prompt treatment a cat can go into kidney failure.

Removing the anthers, the pollen-bearing tips a florist often snips off to prevent staining, reduces the risk but does not remove it, because the petals, leaves and vase water are toxic too. If you cannot find out whether there is a cat, choose something else.

• True lilies include the oriental, trumpet and longiflorum types, and the hybrids that turn up in most mixed bouquets.
• Daylilies are just as dangerous to cats, though they appear more often in gardens than in vases.
• Peace lilies (Spathiphyllum) and calla lilies (Zantedeschia) are not true lilies. They irritate a cat's mouth rather than damaging the kidneys, which is less serious but still miserable for the cat.
• Carnations and chrysanthemums can also upset a cat's stomach or skin, so in any home with a cat, keep flowers out of reach.

If a cat may have touched or chewed a lily, call a vet straight away, before any symptoms appear. Vomiting, drooling, loss of appetite and lethargy can follow, and early treatment makes a large difference to the outcome.

Heavy scent in a small room

Scent is made of volatile compounds that the petals release into the air, and a warm, still room concentrates them. Oriental lilies, hyacinths, tuberose, stocks and freesias can be lovely in a hallway and overwhelming in a small bedroom or studio flat, where there is no escaping the smell.

For most people that is only a matter of comfort. For some it is more: strong smells, including perfume and other fragrances, are a common trigger for asthma symptoms, and many people who get migraines say the same of strong fragrance. Someone unwell or sensitive to smell may find a powerfully scented bunch hard to live with, then feel guilty moving it outside.

When the room is small or the recipient's sensitivities unknown, choose flowers that look generous but smell of little: most commercial roses, gerberas, carnations, tulips and hydrangeas. Keep heavy perfume for people you know love it.

Yellow, and what older traditions made of it

Yellow is now the colour florists reach for when a bouquet needs to say friendship, congratulations or get well soon. It has not always been so innocent. In the Victorian language of flowers, the yellow rose stood for jealousy and a decrease of love, and a few people raised on those meanings still notice it.

Other traditions tie yellow to parting. In some families yellow flowers are thought to signal separation or an ending, which makes them an odd choice for a partner. In Mexico, yellow and orange marigolds are the traditional flowers of the Day of the Dead, placed on altars and graves, so a bunch of marigolds can feel more like remembrance than celebration to someone who grew up with that custom.

Treat all of this as folklore rather than rule; most people read yellow simply as sunny. It is worth a second thought for romantic flowers, for a family that keeps these meanings, or for an apology, where a hint of jealousy is the last thing you want.

Checking without spoiling the surprise

You rarely need to ask the recipient directly. A partner, flatmate or relative can usually tell you whether there is a cat, whether the home is small, and whether the family keeps flower customs. Then put the constraint in the note to the florist in plain words: no lilies, an odd number of stems, nothing strongly scented. A florist in the recipient's own city makes up the arrangement by hand, so an instruction like that is simple to follow. When you know nothing at all, these defaults are safe:

• An odd number of main flowers, which offends nobody.
• No lilies unless you are certain there is no cat in the home.
• Mild-scented flowers for small rooms and unknown sensitivities.
• No chrysanthemums for anyone raised in France or Italy, and nothing all-white for a celebration if the family links white flowers with mourning.