Why does my hydrangea not flower? This most commonly asked question about hydrangeas, especially in colder climates. The answer is not always a simple one but I’ll try to answer the question in this post.
Reasons for not flowering depend very much on the type of hydrangea you are growing. It is therefore important that you know the type. Have a look at Hydrangea Identification to find out which type you have.
Why do Hydrangea Not Flower
The following is a list of some of the reasons for getting few or no flowers on your hydrangea.
A common myth is that fertilizer will make a plant flower but this is rarely the problem. If your plant is growing and looks healthy it has enough nutrients to flower. Whatever you do, don’t start throwing fertilizer at your hydrangea.
Bloom Boosters do not work. See Bloom Boosters – Fertilizer Nonsense #5, to understand why.
Lack of Fertilizer
A lack of fertilizer is almost never the cause for non-flowering. In fact, over fertilizing is probably a more common problem.
Shrubs in the landscape do not normally need to be fertilized. In 10 years I have never fertilized one of my shrubs.
Get a soil test done if you feel there is a nutrient deficiency in your soil. Then add the fertilizer you need – not something you don’t need. To better understand how to fertilize properly have a look at Fertilizer Nonsense #3 – All Tomatoes Need The Same Fertilizer.
Mulch with wood chips or compost, to provide a slow steady feed for all your shrubs.
Too Much Fertilizer
Too much nitrogen will result in lots of large leaves and few flowers (ref 1).
Too much or too little water can prevent flowering.
The idea that hydrangeas need lots of water is a myth. They do not need any more water than other types of shrubs. Water well during the first year and then treat them just like other shrubs. H. macrophylla and H. quercifolia do enjoy more moisture but they don’t need to be grown wet.
My hydrangea rarely get extra water. They need to live on what nature drops on them and they do quite well. You may need to water more in warmer or drier climates – just like other shrubs.
Sudden Cold Snap
Hydrangeas are slow to get conditioned to cold weather in the fall and they come out of hibernation early in spring. This means that flower buds are easily damaged by a sudden cold spell in fall or a cold snap following warm weather in spring. Buds that are damaged by cold will not open, or open improperly.
Buds below the snow line are protected from cold weather and it is common to see shrubs bloom on just the lower branches. The buds on the upper branches don’t open because they were killed off by cold weather.
Bud kill due to cold is only a problem for hydrangea that form their buds on old wood. These plants form buds in mid-summer and early fall for flowering the following spring. This group includes H. macrophylla, H. serrata and H. quercifolia. The climbing hydrangea, H. petiolaris, also forms buds on old wood, but the buds seem quite winter hardy even in zone 4.
H. arborescens, and H. paniculata form buds on new wood in late spring for flowering the same summer. The buds on these types of hydrangea are rarely affected by cold weather.
Each type of hydrangea needs to reach a certain age and size before it will flower. It might have been flowering in the pot when you bought the plant, but the transplanting process sets it back. It may need a year or two to establish itself and become a healthy plant.
Where the above ground growth gets killed off each winter, hydrangea may have trouble getting big enough to flower.
Most of the bush hydrangea bloom on fairly young plants, but the climbing hydrangea can take many years before it will flower. There is nothing you can do except wait.
Not Enough Sun
Do hydrangea prefer sun or shade? It really depends on both the type of hydrangea and the climate.
The following is a general guide.
In US climatic zones 6 or colder:
- All hydrangeas can take full sun provided they have enough moisture.
In US climatic zones 7 and warmer:
- Some shade should be provided for H. macrophylla, H. serrata, H. petiolaris and H. quercifolia. The preference for H. quercifolia is full shade. H. arborescens can take full sun in warm climates but probably does best with some shade. H. paniculata can take full sun even if dry.
If your hydrangea blooms on new wood, is a good sized shrub and is not flowering, try to move it into more light.
If you prune at the wrong time of year and cut the buds off you will not get flowers – it is that simple.
Hydrangea that bloom on new wood should be pruned in late winter. Those that bloom on old wood should be pruned right after flowering which ensures that new buds have not yet formed.
It is a myth that hydrangea need hard pruning to flower. All of them will flower with no annual pruning.
In addition to the cold snap discussed above, buds and stems can also be killed by cold mid-winter temperatures. In colder climates it is quite possible to have the stems die back due to a cold winter and still have a live plant. The crown of the plant is hidden below ground and receives some protection from the soil.
Plant hardiness ratings apply to the crown of plants and not to buds. Most H. macrophylla are quite hardy in zone 5 and will survive winter just fine. The buds and old stems are not hardy in zone 5 and die off each winter. Such plants grow fine each year, but never flower. Unfortunately, because of their very popular blue flowers these hydrangea are regularly sold in zone 5.
H. serrata and H. quercifolia are also hardy in zone 5, but their flowers are not. They rarely flower in colder zones.
If your hydrangea is one that forms buds on old wood and you have winter dieback of the stems, you will probably not get any flowers.
The climbing hydrangea will flower in zones 4 and 5.
The Endless Summer Disappointment
People in the north desperately want to grow large blue mophead hydrangeas but winter kills off the buds. All this changed with the introduction of Hydrangea ‘Bailmer’, Endless Summer™.
Endless Summer blooms on both old and new wood. This is great news for us northerners. Even if the old wood buds get killed off, the plant will make new buds on new wood – or so the advertising would have you believe.
The reality is that this cultivar does very poorly in zone 5. It may be able to flower on new wood, but it rarely does. The internet is full of people wondering why this miracle plant is not performing – what are they doing wrong? Nothing. In zone 5 it is a dud. Replace it with something better.
Not all cultivars will do well in all locations. Some just flower poorly.
Read about more hydrangea myths here: Hydrangea Myths
- Why Don’t My Hydrangeas Flower?; https://www.ces.ncsu.edu/fletcher/staff/rbir/hynonflower.html