Plants for solitary bees

Small bees need reachable flowers

A solitary bee is typically a few millimetres long with a tongue to match, and it cannot enter a deep corolla at all. What it can use is an open shallow flower with the nectar accessible at the surface — which describes most of the daisy family, most of the carrot family, and most of the small early blossom on trees and shrubs.

This is why an apparently unremarkable umbel of wild carrot or hogweed is worth more to solitary bees than a spectacular double-flowered ornamental. It is also why doubles are worse than useless: breeding for extra petals converts the reproductive parts into petals, so the flower often has neither nectar nor pollen behind an entirely convincing display.

Short lives mean the calendar matters more than the list

An individual solitary bee is on the wing for perhaps three to six weeks, and different species occupy different weeks from March to October. That has an awkward implication for garden planning: a plant that flowers superbly for a fortnight supports whichever species happen to be flying in that fortnight and no others. Continuity is not a refinement here, it is the whole requirement.

• March and April: willow, blackthorn, dandelion, crab apple. This is when the spring mining bees fly and there is nothing else.
• May and June: hawthorn, bird's-foot trefoil, selfheal, buttercups, the first umbels.
• July and August: wild carrot, yarrow, hogweed, knapweed, poppies for the pollen specialists.
• September and October: ivy above all, which carries the ivy bee and much else.

And the ground matters as much as the border

Around seventy per cent of these bees nest in bare soil, and most of the rest in stems and dead wood. A garden with faultless forage and no bare ground, no standing stems and no dead wood supports visitors rather than residents. The two have to be provided together and close together, because a small bee's foraging range is measured in hundreds of metres rather than kilometres.