In May the flowering trees begin to come to an end and the herbaceous perennials take over. This is when the meadows would have started to become the  main source of bees food supply and that is why gardens as such an important substitute. My star bee-plants for May are the poppies and geraniums.  All poppies are excellent but the perennial 'oriental' poppy is so reliable, in any sunny position, and provide masses of pollen just at time when the bees are growing their numbers and needing pollen to feed the brood. Shrubs are also useful in may: ceanothis, weigelia and hawthorn.