If you like plants that do their thing with little help from you then stay away from any of the hundreds of cultivars of this group of Hydrangeas. They’ll grow, but if you see one in flower it was probably just purchased in bud or bloom and immediately planted.
The second year all you’ll see is mound of large, lustrous, fleshy, dark green leaves. But if you thrive on gardening challenges that promise outstanding rewards these shrubs are for you.
Hydrangea macrophylla, is native to Japan and is flower bud hardy only as far north as zone 6, through the southern third of Missouri and Illinois. Central Illinois is in zone 5. This is important because this group of Hydrangeas produce most of their flower buds for next year on wood being produced this year. If those stems and buds are subject to temperatures much below 0° the result is flower bud and stem kill to the crown.
The cultivars of Bigleaf Hydrangeas are divided into two groups. Hortensias, aka Mopheads, are the ‘snowball’ type with large, round clusters of sterile flowers. The Lacecaps have clusters with a flat outer ring of fertile showy flowers surrounding a center of non-showy sterile blooms. Sometimes there’s a showy blossom or two scattered in the center ring.
Culture is the same for both groups: Plant them in a moist, well-drained soil liberally amended, up to 50%, with peat moss in full sun or partial shade
Afternoon shade is best. A bright but protected area, a microclimate such as a courtyard for instance, is ideal. They also love water so don’t let them dry down in the summer.
You must protect them during the winter to have any chance of flowers next year. In early to mid-November wrap the entire plant with burlap. Then put a circular wire frame around it and fill it with straw, firming it in. The frame needs to be large enough to offer at least a foot of straw on top of and around the stems.
If it’s a mild winter and you’ve done everything right and are lucky flowering will begin in mid-summer. Prune immediately after the flowers are no longer effective.
The flower colors
You notice I haven’t mentioned what color the flowers are. That’s because it usually varies tremendously depending upon the pH of the soil and more luck if you have any to spare. A soil test to determine the current pH of your soil is a must if you are serious about growing Bigleaf Hydrangea. Blue flowers, the color everyone seems to want, are produced when the pH is 5.5 or lower, 6.5 and above produces pink flowers. Most of our soils are somewhere in between so, assuming the plants bloom at all, we end up with flowers that are rather sickly pinkish-bluish hue. You can manipulate the pH with peat, sulphur and aluminum sulfate somewhat but it may take a few years to get the color you want. Did I mention that these plants are a challenge?
If you’re still determined to try a Bigleaf Hydrangea here are the cultivars we offer.
*Each year your hydrangea will develop new growth. If your variety “blooms on new wood” then it will be blooming each year on its new branches. Since different varieties of hydrangeas have different qualities, be careful when and how much you prune.