All 89 bee plants
Viper’s bugloss pollen
Echium vulgare
Blue grey, in the blue / purple range.
FloweringJune to August
PollenVery good
NectarYes
SeasonSummer
WhereWaste and verge
One of the best nectar plants on chalky and sandy ground.

Easy to mistake for these
Closest pollen colours in our set, measured the same way the pollen identifier scores a match. Colour alone will not settle it, so check the flowering months and what is actually growing near your hives.
Out at about the same time
Saw a load like this going in?
Sample the colour against all 89 plants, then keep a forage record per hive.