Bloom On New Growth
Michael A. Dirr is one of the people responsible for giving us the Hydrangea macrophylla cultivars that bloom on new growth.
In areas that experience late freezes in the spring, buds in the stems of the hydrangeas that bloom only on last year's branches, are killed.
The new cultivars bloom on new as well as old branches. So the new branches will give us flowers even if the buds in the old branches get frozen out.
Dirr's best known cultivar is aptly named ‘Endless Summer'. It's a re-bloomer that doesn't need pruning.
All hydrangeas give a romantic look to a garden as they have big lady-looking flower heads made up of small individual flowers.
The densely packed round shaped clusters are called mopheads, flower heads that include some open and other unopened flowers are called lacicaps, and flower clusters that are elongated are called panicles, and they have the word paniculate in their name.
White bloomers such as hydrangea arborescens ‘Annabel' bloom late on new stems so are impervious to harsh winters and springs. But we lust for the blues which need acidic soil (with a pH of 0 to 7).
White aluminium sulphate can be added to the soil to increase acidity; it really doesn't always work well. However, those of us with lime in our soil can grow wonderful pink, white and red flowering hydrangeas that are also rewarding.
[Michael A. Dirr Hydrangeas for American Gardens (2004) Timber Press]