What pollinators can and cannot use

Flower shape is everything. A honeybee has a tongue roughly 6mm long. A bumblebee manages 10–12mm. Hoverflies have virtually no tongue at all and need flat, open blooms where nectar pools at the surface. If you plant flowers with nectar hidden behind tight petals or deep tubes, you are hanging a sign that says 'closed'.

Double flowers are the worst offenders. A double dahlia, a double rose, a double petunia — the petals are beautiful, but they are mutated stamens. There is often no nectar and no pollen. The flower is sterile. Pollinators land, realise, leave. Meanwhile a single-flowered dahlia like 'Bishop of Llandaff' or 'Magenta Star' is mobbed by bees from July to the first frost.

Colour matters less than you have been told, but pollinators do see ultraviolet patterns we cannot. Blues, purples, whites and yellows score consistently well. Reds can be tricky — bees struggle to distinguish them from background green, though some bumblebees and all butterflies manage fine. If in doubt, choose an open, simple flower in a cool colour and you will rarely go wrong.