There is something about full-flowered, rich blue Hydrangea blooms that sets your heart a’flutter. Maybe this only happens to those of us in colder zones (6 or lower) that find it so rare to have ANY flowers on our bigleaf Hydrangeas (pictured – Hydrangea macrophylla CITYLINE ‘Venice’).
Let’s face the brutal facts. ALL bigleaf hydrangeas form their flower buds in late summer and early fall for the following year’s show. In colder regions these buds can freeze to death due to bitter temperatures and/or high wind chill factors. Fluctuating temperatures can also be a terminating factor, as flower buds are fooled into breaking dormancy by unusually warm winter days and then they are blasted by a fast drop in temperature. It doesn’t seem fair…..
You can help reduce the odds of flower bud damage by planting Hydrangeas out of the path of winter winds and near foundations, stone structures or boulders that store heat during the day and release it at night. Burlaping Hydrangeas or encircling them with chicken wire and stuffing raked leaves into the cavity around the stems can also provide some helpful insulation. (photo Missouri Botanical Garden)
But let’s be on the positive side and assume you’re going to have a mass of flowers next year. If your heart is set on blue blooms, then do a soil pH test (Rapitest is an inexpensive, two-minute test that is simple to do). For blue blooms the soil pH should be between 5.0 and 6.0. If you need to lower the soil pH, then apply elemental sulfur to the soil around the shrub, scratch it into the top few inches, and water in well. Espoma’s Organic Soil Acidifier is the finest, most effective soil acidifier available and the only one that I use. This pH correction takes up to six months to occur. That is why a fall pH treatment can make such a difference next year! You can retest the soil in the spring and if a further correction is needed, do so then. The application directions and recommended amounts on are the bag. For more about Espoma’s Organic Soil Acidifier and where to purchase it, click here.