There are two main groups of hydrangeas. The ones we can grow in Edmonton (Zone 3a) are plants that bloom on new growth (this year’s stems). They are showy and “fluffy”, but not usually blue or hot pink. The hydrangeas that are hardy in our climate are pale green and soft whites.
These hydrangeas, which form their buds in early summer on new growth, will flower reliability each year.
• Panicle hydrangeas ( H. paniculata) are hardy to Zone 3 and boast fat, cone-shaped flower heads. They are a good choice for a beginner. The most common cultivar is’Grandiflora’, or P.G. (PeeGee) after its initials, a big old-fashioned floppy shrub that is 10 to 15 feet tall.
• Smooth hydrangeas (H. arborescens) or “snowballs” are excellent for cold climates, flowering reliability in Zone 3. The flowers look like oversized white-flowered pop-poms. Look for cultivars ‘Grandiflora’ and ‘Annabelle’ which produce large blooms in late summer.
The other type of hydrangeas are those that Edmontonians can enjoy inside or on the patio in the summer. These are hydrangea that bloom on old growth (last year’s stems). They include:
• Oakleaf hydrangeas (H. quercifolia) exhibit incredible bud hardiness and thrive in Zone 5. This graceful plant is noted for its spectacular fall colors that range from red to purplish burgundy. The flower heads turn a rich brown that lasts all winter. Try ‘Snow Queen’, ‘Snow Flake’, and ‘Alice.’
• Bigleaf hydrangeas (H. macrophylla) are the most common species and come in two flower shapes: Mopheads (or Hortensias) which are hardy to Zone 6 and bear large, ball-shaped flowers and lacecaps which are suitable for Zones 5 to 9 and form airy, elegant, flat-topped clusters of flowers. We love ‘All Summer Beauty’ (Hortensia) which has profuse, dark blue flowers, pinker on soil near neutral. ‘Nikko Blue’ (Hortensia) is vigorous, with large, rounded blue flowers. ‘Blue Wave’ (Lacecap) produces rich blue to mauve or lilac-blue to pink flowers.
• Climbing hydrangeas are just magnificent, lighting up the trunk of a tall tree. This vine blooms from late June to early July, exhibiting flat, lace, creamy-white flowers against glossy leaves.