This will be the second column in a series on bigleaf hydrangea. Some people may know the bigleaf hydrangea, Hydrangea macrophylla, as either French, Japanese or even snowball hydrangea. I think the overall popularity of this plant is the ability of the owner to change the bloom color from either pink to blue or from blue to pink.
This year, the hydrangea plant at our home is displaying beautiful blue blooms. In our most recent cokumn on bigleaf hydrangeas, I covered multiple topic areas from the different hydrangea cultivars and groups, proper planting locations, how to plant, fertilization and watering needs along with the background on bloom color along with ways to change the bloom color.
Today, I will cover more topic areas on bigleaf hydrangea with the help of a UGA publication on this landscape plant by retired UGA Horticulturist, Gary Wade.
I think the most popular characteristic of a bigleaf hydrangea is the bloom color. Keep in mind that there are over 500 hydrangea cultivars that are divided into two groups.
There is the hortensias group which will have the large snowball-appearing flower clusters.
There is also the lacecapes, which will have more flat top flowers that will have more non-showy flowers in the center and more showy sterile flowers on the outside.
As part of review, the bloom color is based on the presence or lack of aluminum compounds in the flowers. If you have aluminum, you will have more blue blooms, while on the flip side if the aluminum is in small amounts, you may have an in between color. If aluminum is not in the flower, you will have pink blooms.
On our hydrangea at home, we have pretty blue flowers, but I think we have some in that in-between stage also. If you want to change the bloom color from pink to blue, you need to broadcast 1⁄2 cup of wettable sulfur per 10 square feet and water in. To go from blue to pink, you need to broadcast one cup of dolomitic lime per 10 square feet and water in. This is a gradual way to change the flower color and could take a year to see a bloom color change.
A way to see a bloom color change sooner, could be through the use of soil drenches. If you wish to see blue blooms or blooms that are more blue during the active growing season, you can dissolve one tablespoon of alum (aluminum sulfate) in one gallon of water and then drench the soil around the plant in March, April and May. If you want to achieve pink blooms, you can dissolve one tablespoon of hydrated lime in one gallon of water and drench the soil around the plants in March, April and May. One important reminder is to not let the liquid solution get on the foliage because you may see leaf damage.
Again, many people consider bigleaf hydrangea a popular landscape item because of the bloom color and may find it fun to change the color. It is a letdown when the plants fail to bloom at all.
Sometimes the failure of the hydrangea to bloom can be traced to poor management of the owner.
There are several reasons that can cause a hydrangea not to bloom. Those reasons are winter injury to flower buds, growing the hydrangea in too much shade, applying too much nitrogen and also pruning at the wrong time of year. Keep in mind that bigleaf hydrangea will form flower buds in late summer for the next year. Avoid pruning a bigleaf hydrangea in late summer, fall or winter. If you do prune hydrangea then, you will be removing the flower buds.
I will remind you that bigleaf hydrangea can do well with a few light fertilizer applications in the growing season. General purpose fertilizers such as 8-8-8 or 10-10- 10 given to the plant at the rate of one pound per 100 square feet in March, May and July can be helpful. One pound of these fertilizers is equal to about two cups. You do not have to pull back mulch to fertilize, but you do need to water the fertilizer in soon after applying.
Another reminder is proper watering. This summer could end up being wet overall, but you do need to note water needs of hydrangea annually.
You can put bigleaf hydrangea in the water demanding group of plants. You need to be prepared to water the hydrangea when you see signs of wilt when rainfall has been lacking.
It is especially important to avoid plant stress in the spring during flower formation.