Daffodils and narcissi have a murderous tendency once put into a vase. When cut and mixed with other flowers they give off a toxic sap that kills other blooms within a day or two.

The vase life of daffodils and narcissi is one of the research projects being undertaken by scientists.

There are flower foods that neutralise the poison from daffodils and narcissi. If kept cool the flowers can last a week. But different formulas may produce longer lasting blooms.

Flowers can also be divided into thirsty water drinkers, and the abstemious, which use water sparingly. Roses and tulips are ideal companions in a vase but are both heavy drinkers so need regular topping up. Gerberas and sunflowers with their hairy stalks, however, thrive on little water — too much and the stalks get soft.

These expert tips do not touch the taboos around flowers. Many people still shudder at the sight of red and white flowers in a vase. They denote blood and bandages and are regarded as the symbols of death.

Few doctors and nurses will allow the combination in hospital, though modern florists dismiss this as superstition.