I was looking at the trial of marguerites, Argyranthemum, sometimes known as cobbitty daisies, at the Royal Horticultural Society's garden at Wisley near London this week. One hundred and seven different varieties from around the world all grown in one place. A great opportunity to compare.

Two things struck me. Firstly, the old varieties like 'Jamaica Primrose' were only just starting to flower while modern varieties were covered in flowers. And already plants of the old varieties were generally much larger. But, more importantly, I was struck by the fact that while the flowers of some faded harmoniously the flowers of others deteriorated badly and as they faded they detracted from the display.

This is important because if you have to pinch off the flowers before they're finished the impact is dramatically reduced.

In the picture, the plant on the left is Summit Pink ('Cobsing') and the single flowers open in rose pink then fade to white. Very pretty and with a bonus: as the flowers finally die, the petals roll back as they turn brown and are hardly visible at all so no deadheading is needed.

On the right, San Vicente ('Ohmadsavi') opens a deep magenta rose then becomes paler and paler at the tips of the petals at the same time developing an odd little white crest in the middle. The result is a mess which could only be improved by cutting off half the flowers in the picture. What's more, as you can see, as the petals turn brown they remain on show. Not good.

The classic plant for ageing disgracefully is Achillea 'Fanal', often known as 'The Beacon'. As the tiny flowers first open, the flat heads are a brilliant scarlet. Then it all goes wrong, and as the later flowers are at their peak the earlier ones have turned the colour of dirty dishwater. Of course, you cut them off – but then the display is certainly much brighter, but very very thin.

The ability to fade harmoniously is not always a feature that can be easily appreciated when you come across an unfamiliar plant in flower in the nursery. But look carefully at all the plants on offer and it's often possible to look into the future and see how the flowers will mature.