From time to time, I hear fans of Hydrangea (Hydrangea macrophylla cvs. and H. serrata cvs., USDA Hardiness Zone 5-9) tell me the news of their heartbreak, because a precious shrub will not bloom. They have been patiently waiting to see if this will be the summer when their mop heads or lace flowers appear, but they are disappointed. This problem is not uncommon and is easy to solve. All they need to do is understand how these woodland plants grow and choose those that are hardy in the climate.
Avoid too much shadow and too much nitrogen
When it comes to hydrangea that refuses to bloom, two words to remember are "too much." Large-leaf hydrangeas in most parts of the United States grow well in shade; however, too much shade can result in gorgeous leaves without flowers. The high shade created by deciduous trees or evergreen plants is very suitable for large-leaf hydrangeas in the east, midwest, and northwest. In California, any shade you can find, as long as it is not too dense, seems to be effective. But the hydrangeas located near the misty coast and in the northern part of the country need no shade at all.
If your hydrangea is not blooming, you may prune it at the wrong time. Read about pruning hydrangeas.
Another problem may be too much fertilizer. High-nitrogen fertilizers will produce beautiful leaves and few flowers (if any). Large-leaf hydrangeas can tolerate very high fertilizers without showing signs of burning fertilizer, so be moderate. Too much water and too much dryness can also lead to lack of flowers.
Choose from many proven hardy varieties
Many bigleaf hydrangea varieties enter the garden center or mail-order catalog before conducting the landscape cold tolerance test. This is why researchers like Sandra Reed, a research geneticist at the National Botanic Gardens, and staff at the Mountain Horticultural Crop Research and Extension Center at North Carolina State University, have been evaluating the cold tolerance of hundreds of varieties. After five years of research in test fields in Missouri (Zone 5), Tennessee (Zone 6), and North Carolina (Zone 7), we found that these choices had the most consistent flowers in areas with cold winters. In zones 5-9, everyone is very hardy.
One of the best blue flower mops to date is "All Summer Beauty". Its sky blue flowers have white eyes and mature to full blue. 'Nikko Blue' is a variety with clear blue flowers and an excellent shrub. Both have relatively large and abundant flowers that reappear in autumn, but their reliability under different conditions has won my favor.
'Mathilda Gutges' is a good choice because its deep purple-blue flowers are just above the leaves. Like all other large-leaf hydrangeas, the color of "Matilda Gucci" can range from medium pink to blue, depending on the soil conditions. "Générale Vicomtesse de Vibraye" consistently produced the largest flower head among all the hydrangea we evaluated, which made me vote for it. In our acidic soil, this cultivar will produce light blue flowers in the rainy season, up to 18 inches in diameter; in other areas, it will produce beautiful pink flowers.
If the pink mop head is more suitable for your style, "Glowing Embers" (synonyms. "Alpenglühen" and "Alpenglow") is the best red-pink variety I have seen in this series. "Masja" followed closely with its compact habits and charming pink flowers. But for those gardeners who like white flowers, I highly recommend "Madame Emile Mouillère". Alas, this pure white variety is not reliable for us in the exposed southern part of the Blue Ridge Mountains, but in a sheltered place, it is a precious gem.
Both'Bluebird' and'Tokyo Delight' have cute, flat, doily-like flowers, which are very reliable. The large pale blue or pink flowers of "Tokyo Delight" gradually fade to almost white, while the"Bluebird" blooms completely blue flowers on its charming and exuberant leaves. When the "Blue Bird" flower sets seeds, the sterile florets will turn up, and the pink underside will be exposed regardless of the pH of the soil.
In terms of overall beauty, my favorite lace hat is ‘Coerulea’ because it has very nice leaves and light blue flowers will reappear in autumn. "Lilacina" is also an exquisite choice. Although it is always purpler than blue under our conditions, I have seen it show extraordinary pink flowers in other areas. 'Lilacina' doesn't bloom much when it's young, but patience pays off. As the plant matures, its beautiful flowers will increase a lot, and it will bloom even in heavy rain.
For something a little out of the ordinary, "Lanarth White" is a reliable white flowering lace hat that produces a lot of flowers and occasionally re-blooms in the fall.
Bigleaf Hydrangea and Serrata cvs
- Origin: These deciduous woodland shrubs are native to Japan. There are more than 400 known cultivars between these two species.
- Hardiness: USDA Cold Hardiness Zone 5 to 9. Depending on your location, they perform best in full sun to partial shade.
- Conditions: They like moist, well-drained soil, but yellow leaves appear in highly alkaline soil, which is a symptom of chlorosis.
- Propagation: Use softwood or semi-hardwood cuttings to propagate new plants in late spring or early summer.
- Pruning: Pruning dead wood on shrubs in early spring. Avoid pruning the healthy growth of the previous year, because flowers will grow on old wood.
- Size: The height of the plant varies from 3 feet to 6 feet, but wind and cold temperatures can cause damage and hinder the overall bush size.
If you have met all the cultural needs of the hydrangea, but still haven't bloomed, it may be helpful to understand how its buds are produced. On the large-leaf hydrangea, the flower buds formed during the previous year's growth and are called old wood. Therefore, destroying or removing these buds will prevent your plants from blooming.
Bigleaf hydrangeas require very little maintenance and pruning, with the exception of removing dead wood from shrubs in early spring and possibly dying the flowers for aesthetic reasons. Any pruning (including the help of deer) for healthy growth in spring, autumn or winter can result in reduced flower production. If you must prune the hydrangea to control its size, the only time to reduce healthy growth is in the summer after the bush blooms.
Cold winter temperatures usually kill flower buds. This problem can be solved by planting large-leaf hydrangeas on hillsides facing north or east, rather than planting them on the south or west slopes, which are the first areas to warm up at the end of winter, leading to excessive flower buds blossom early. Choosing hardy varieties and locating plants under the canopy of evergreen trees can help avoid winter deaths. Some people use temporary deep winter mulch to protect the lower buds from cold temperatures. I have also seen gardeners wrap plants in burlap cocoons every winter, successfully protecting their plants. However, in areas where winter temperatures vary widely, protection may only provide limited help. During the short warm period of late winter, when flower buds are triggered to break dormancy, they are usually killed by the return cold temperature. In this case, there is nothing you can do except practice these protective measures and hope that nature will cooperate.
By better understanding how these plants grow and by choosing options that can withstand the cold, the possibility of having outstanding performance is in our favor.
Modify your soil to get the color you want
The flower color of the large-leaf hydrangea depends on the pH of the soil and the amount of aluminum in the soil (unless it is a white flower variety that has no pigment and is unaffected). Hydrangea can easily absorb aluminum only when the soil pH is low. Therefore, the more aluminum in the soil and the lower the pH (acidity), the bluer the flowers will be. The less aluminum in the soil and the higher the pH (alkaline), the more pink the flowers will be. This sounds simple, but since there is no soil test available for ordinary gardeners to determine the aluminum content, you should let the plant be your guide. Let your plants grow underground for a year, and then go through a flowering cycle. If your flowers are blue, your acidic soil contains aluminum. If your flowers are pink, you either have no aluminum or the pH is alkaline. To get the color you want, you can simply test your soil pH and modify it accordingly in early spring.
Acidic soil with aluminum = blue flowers
For pink flowers, add lime and phosphorus to increase the pH and prevent the absorption of aluminum, or use soil-free or aluminum-free planting media to grow in raised beds or containers.
Alkaline soil = pink flowers
For blue flowers, add organic matter such as compost or compost around the base of the plant to lower the pH.
Acidic soil without aluminum = pink flowers
For blue flowers, aluminum sulfate is added to increase the aluminum content.
Alkaline soil without aluminum = pink flowers
For blue flowers, aluminum sulfate is added to lower the pH and increase the aluminum content.