Plants that bloom in May in Zone 3 with green flowers

Coral Bells

Grown mostly for dramatic foliage, but the tiny bell flowers are a bonus.

Lady's Mantle

Chartreuse frothy flowers and pleated blue-green leaves that hold water droplets like mercury. The ultimate filler plant.

Ostrich Fern

Tall vase-shaped fronds that unfurl from fiddleheads in spring. Spreads to form dramatic colonies.

Rhubarb

Huge leaves and thick red stalks give a lush look while supplying tart harvests.