MAY BLOOMING PERENNIALS
Aquilegia or Columbine will grow in a sunny spot or partial shade. They come in a wide variety of colors, including many two-colored flowers. They re-seed nicely.
Geraniums are great in perennial borders. They prefer full sun and usually come in shades of pinks and blues.
Brunnera macrophylla or forget-me-nots are a lovely short perennial that has blue flowers that continue for a couple of months. Some shade.
Primula vulgaris or English primrose have cheerful flowers and crinkly leaves. Some shade.
Caltha palustris or Marsh Marigold is native to Europe as well as North America. They like boggy or wet soil – you can even grow them right in a pond. Yellow flowers. The plant will go dormant by mid-summer. Full sun or a little shade.
Dianthus or Pinks are a staple of the English garden. Being short, they do well as a border along the front edge of a perennial garden. Also try them under larger plants like roses. The old-fashioned varieties will be the most fragrant. Full sun.
Geums will bloom through the summer. They come mostly in reds and oranges, and look best in large groups. Full sun.
Lily of the Valley is a sweet-smelling, old-fashioned white flower. Likes partial shade and does well planted as a ground cover under trees.
Lupinus or Lupines are charming when planted in front of a white picket fence. They have tall spiked flowers in a wide variety of shades, pinks and blues being the most traditional. They tend to be short-lived plants, so let them re-seed. Likes a little shade.
Pulmonaria or Bethlehem Sage has white or pink flowers above a clump of white spotted leaves. They prefer some shade.
Violas are a very adaptable flower. Tuck them into containers or hanging baskets, or use them as edging along the front of a bed. Some shade, wide variety of colors.
MAY BLOOMING SHRUBS
Cytisus x praecox or Scotch Broom is a shrub that grows to 4 feet. They are a member of the pea family, so their flower stalks resemble pea flowers. Traditional in yellow shades, but now come in rose pinks, burgundy, white and orange.