How did Your Hydrangeas Bloom this Year?

So how did your Hydrangeas bloom this year?

One the most common questions I get, is "Why won't my Hydrangea bloom." Of course they're talking about the beautiful species called Hydrangea macrophylla (Big Leaf Hydrangea).

.... [Not sure what type of Hydrangea you have? Click here]

This plant is extremely popular because it is the most colorful of all the species. This plant can be categorized into two main groupings: Mopheads (snowballs) and Lacecaps. The Mopheads are large round clusters of sterile flowers and the lacecaps are flat heads composed of both fertile and sterile flowers. The mopheads are the most popular because we tend to love the gaudy. The lacecaps are gaining in popularity and are considered by many, including myself, to be even more beautiful because of their delicate looking nature.

The key message here is that Hydrangea macrophylla is it sets its flower buds in the fall when night temperature fall below 60F/16C. Thus the flower buds must survive the winter if they are to mature into big beautiful flowers the following summer. [We call this blooming on old wood.] This is the crux of the problem - a hard winter, an early fall freeze, a late spring freeze, or untimely pruning will damage the flower buds and result in a loss of flowers.

So what is a person to do if they want to be successful with Hydrangea?

1) Understand how and when to prune

Big Leaf Hydrangea does not require much pruning once established, but proper pruning is critical if expect to see flowers.

The best time is in early to mid-July. Prune back any non-flower stems back to about six inches from the ground. This helps to produce short stems which keeps the next crop of flower buds close to the ground where they can be more easily protected from winter damage. It is critical that you cease pruning by the end of July. This allows time for the new flower buds to form and harden off prior to winter.

2) Shut the plants down before winter

Hydrangeas will continue to grow as long as there is ample water, fertilizer and warm weather. Later season growth is tender growth and more prone to winter injury, so useful to shut the growth down before winter comes. In late summer and fall, stop fertilizing and cut back on the water. Don't worry if the plant looks severely wilted, just provide enough water for the plant to survive. This will slow down the growth, help to induce flower bud formation and make the plant less susceptible to an early freeze.

3) Mulch and Protect

In late fall, mulch the base of your plant with six to ten inches of bark or peat moss. This will protect the buds on the short stems (the ones you pruned in July). Apply the mulch after the onset of cold weather but before the temperature falls below the teens. This mulch will be removed or spread out in the spring after the danger of frost has past.

4) Grow Varieties that Bloom on both Old Wood and New wood [rebloomers]

Within the last ten years, varieties have been developed that make buds in both the fall [typical], and during the summer [atypical]. Or putting it another way, they flower on both old and new wood. This means that even if the flower buds are injured in the winter, new buds and flower will form the next summer. This is great news for those of us who live in cold climates.

The cultivars 'Endless Summer', Let’s Dance Moonlight, Let’s Dance Starlight, and 'Forever and Ever' have the ability to bloom on old and new wood alike. These are great selections for the Midwest where it is hard to get Hydrangea to bloom. 'Endless Summer' was the first rebloomer to hit the market, while the Let's Dance series is the newest generation of rebloomers. The Let's Dance series has superior flower color, overall substance and thicker, glossier leaves. They are also less likely to die to the ground in the winter.

Now I know that many people were disappointed with the Endless Summer Hydrangeas this year.

We had a long warm spell in late winter followed by weeks of freezing weather that knocked many Hydrangeas back to the ground. As a result, the old wood buds were killed, and we lost the early-season flowers, even on the rebloomers.

Keep in mind that, even with these new varieties, you get a much better flower display if the old wood buds survive the winter. Sure, if your plants die back to the ground in the winter, you will still get flowers, but they appear later in the season and there are typically fewer flowers overall. So - it still pays to prune properly, keep the buds close to the ground and protect these buds with mulch.

- Another Tip for Rebloomers Like Endless Summer -

If your Endless Summer dies back to the ground in the winter, forcing growth will deliver more flowers and sooner. Endless Summer and other rebloomers have to put on a certain amount of new growth before they will make new buds and flower. So it pays to give these plants extra fertilizer and water to push the growth. Miracle Grow once a week after any danger of frost does the job.

For some people, rebloomers are not the best choice.

If you live in a mild climate where big leaf hydrangea blooms reliably there is no advantage in growing rebloomers. You lucky people have a wonderful array of varieties to choose from, many with superior foliage and flowers. For example - consider the new dwarf cultivars sold under the CITY LINE series. These compact plants form a neat compact plant that is covered with blooms. They also have very vivid flower colors.

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(If you live in a very cold area consider Hydrangea paniculata (Limelight, Pinky Winly, Little Lamb and Quick Fire) and Hydrangea arborescens (Invincibelle Spirit and Incrediball. There are many great new vareities and they are pretty much fail proof.)


----------------Back to Hydrangea macrophylla

Flower color - How to change Flower Color

Another interesting attribute of this plant is that its flower color may change depending on soil p.H.. It is not the p.H. itself that changes the color, but it is the availability of aluminum ions that directs the color. Aluminium has greater availability in acid soils thus the blooms turn blue in acid soils. If the soil is either basic [alkaline] or high in phosphorous, the aluminium is tied up and flowers tend to be pink. The degree of color change is dependent upon the amount of aluminum ions available and the cultivar itself. It should be noted that if you are growing in a container your soil mix you may not have much aluminum availability even at low p.H. levels. Aluminum sulfate treatments would then become necessary to get blue flowers. If you fertilize your plants be aware that you will tie up the aluminum with high levels of phosphorous.

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