Green flowers are more than a curiosity for St. Paddy's Day. While blooms that match their own foliage may not show up too well in the garden, cut and brought indoors their unexpected coloration shines in flower arrangements.
Euphorbias chartreuse blooms hold their own in the garden or the vase. I use these weird, bright little flowers in every flower arrangement I make from March through autumn. If you cut them, be sure and wear gloves for euphorbia sap can cause a rash. And be sure and singe the bottom of the stem - just touch it with a match or lighter for a few moments, and euphorbia will hold up for a week in arrangements.
My favorite primrose is a delicate apple green ruffled beauty called 'Francesca' (below). It blooms April into May, is sturdily perennial, and has long enough stems to make a great cut flower. The mosaic egg next to the primrose in the photo is by Vashon artist Clare Dohna...
Long blooming Rudbeckia 'Green Wizard' (below) is an oddity, with its brown dog-nose cone surrounded by emerald green petals. This one really does disappear in the garden, but well worth growing for a cut flower...
I was just admiring beautiful big bunches of green cut flowers at Metropolitan Market - I hope green flowers are on display more often than just March 17th. From hellebores in winter, to 'Lime Light' hydrangeas and spiky green chrysanthemums in autumn, green flowers are worth tracking down year-round.

