Hydrangeas are seen as an old-fashioned plant, loved for their impressive foliage and big blooms in shades of blue, white, pink and even green.
While colour is soil dependent, hydrangeas thrive in cool, moist shade, and you would think they wouldn’t do well here, but some are more heat and drought tolerant than others, and it’s apparently possible to grow these spectacular plants here, particularly on the north or south side of your home.
I have never grown these beauties, they are something I have always considered a somewhat specialist plant, as it seems a lot of expertise is needed to get such gorgeous displays blooming, and they are not really a plant for the heat.
Having said that, I see gardens here where they are obviously well established and people have managed to grow them successfully, so I thought I should explore and find out what the trick is.
Keep in mind that even sun and heat tolerant hydrangeas benefit from afternoon shade in the heat - too much direct sun will wilt the leaves and stress the plant but using a temporary shade structure might help. Also, they will all need plenty of our precious water during hot, dry weather – sometimes every day.
So far, there are no truly drought tolerant hydrangeas, although some are more tolerant of dry conditions than others, and rich organic soil and a layer of mulch will help keep the soil moist and cool.
Plants cool themselves by drawing water from the roots, which then moves through the stems and out through the leaves, which occurs at a faster rate during really hot conditions.
Smooth hydrangea (H. arborescens)
This is native of the eastern US as far south as Louisiana and Florida and therefore accustomed to warmer climates. It reaches heights and widths of about 3 m and displays dense growth and attractive greyish green leaves. The flowers in bud are green but bloom into a bright creamy white, with some varieties being pink.
These shrubs bloom on new wood, so in late winter or early spring prune them back close to the ground to encourage new growth, plus remove any branches that are sick, dead or damaged.
Bigleaf hydrangea (H. macrophylla)
This is a native of Japan with shiny, toothed leaves, a symmetrical, rounded shape and a height and width of 1-2m. Bigleaf is divided into two flower types – ‘lacecap’ and ‘mophead’. Both are among the most heat-tolerant hydrangeas, although mophead prefers a bit more shade.
Mopheads are sterile, and will not get pollinated, but will bloom on throughout the summer. The shrub’s ‘magic trick’ is that they can change colour - grown in acidic soil, it grows blue flowers, grown in alkaline soil, the flowers will grow in pink (apparently the old story of putting rusty nails in soil does make the soil acidic and turn the flowers blue!).
When pruning, do so right after the shrub finishes flowering. The lacecap difference is that instead of growing round clusters of showy blossoms, this hydrangea grows flowers that resemble flat caps with frilly edges.
They produce showy florets, surrounded by small flowers that look like closed buds, creating a lacey effect. These are fertile and will attract pollinators.
Panicle hydrangea (H. paniculata)
These are a pretty pink, also sun tolerant, needing five to six hours of sunlight but won’t grow in full shade. However, they won’t do well in intense, direct sunlight either. They reach heights of 3-6m, sometimes more, although dwarf varieties are available
Oakleaf hydrangea (H. quercifolia)
These are hardy, heat tolerant hydrangeas that reach heights of about 2 m. The plant is named for the oak-like leaves, which turn reddish bronze in autumn.
The oakleaf is one of the best for drought tolerant hydrangea shrubs; however, the plant will still need moisture during hot weather.
Note that all hydrangeas are poisonous to both us and to our pets, with skin contact causing dermatitis, rash or irritation, as all the plant parts contain cyanogenic glycoside.
All in all, it seems hydrangeas are tricky to grow, and getting the right spot with plenty of water seems to be the key to successful growth.