In the Garden
Ralph Purkhiser, Purdue University Master Gardener
Several people have asked me recently why their spring-flowering shrubs are blooming again. The short answer to that question is that the plants are under stress. That stress may be from extreme heat, drought, disease or even storm damage. But why should stress cause a plant to bloom out of its normal season. The answer to that is a bit more complicated.
The primary purpose of all plants is to reproduce themselves. For flowering plants, that is the reason for the flowers. The flowers attract pollinators, which carry the pollen to other blooms and complete the process of pollination, eventually resulting in the production of seeds, which will fall to the earth and germinate, producing a new plant.
When a plant is stressed, the need to reproduce becomes the highest priority. That is the reason that stressed plants produce flowers, even if it is outside their normal bloom period. Unfortunately, those out-of-season blooms rarely result in completing their mission and producing new plants.
The good news is that most plants will recover from the stress that triggers re=blooming. The key is to find the cause of the stress and do what you can to alleviate it. If the stress has been caused by drought, water the plant regularly if there is not sufficient rain. If the plant has been damaged, pruning out the damaged portions and allowing them to heal may help the plant recover. If the cause is disease, determine the disease and research to see if there are ways to combat that problem.
Certain plants are more prone to re-blooming. Weigelas, for instance, set a major bloom in the spring, but often will sport a lesser number of blooms later in the summer. Weigelas may actually bloom several times, and this phenomenon does not seem to adversely affect the next year’s blooms. Lilacs also are prone to re-blooming. Actually, there are some cultivars of oriental lilacs that have been bred to re-bloom. Bloomerang lilacs may set blooms several times, with a fall bloom that nearly rivals the initial bloom in the spring. The old-fashioned lilacs are especially susceptible to fungal diseases, and many people have noted that the leaves of the lilacs are turning brown and crisp. There is not much one can do to fight a fungus, once it has started, but if the plant is otherwise healthy, it will survive and may set new leaves in a few weeks. Do your best to clean up the old leaves and either burn them or dispose of them far away from the lilacs. This will help reduce the danger of a repeat occurrence next year. In worst-case scenarios, you may have to resort to a complete rejuvenation, cutting the shrub to the ground and cleaning up all of the debris. If the roots are strong, the shrub will re-grow, but it may take a few years for it to bloom again.
Encore azaleas came on the scene a few years ago. These are plants that were bred to re-bloom. Like the lilacs, the fall bloom period is usually lighter than the spring bloom.
The most unusual re-blooming that I have noticed at Sandhill Gardens is on a China Girl blue holly. The shrub bloomed well in the spring and has set abundant berries, which have started to get a little blush color on them. I was looking forward to a good crop for wreath-making this Christmas season. Recently, however, there have been some branches on which the leaves have turned brown, and the rest of the shrub is blooming again. I suspect that heat stress has caused this problem, and the only thing I can do is make sure the shrub gets enough water and keep it as healthy as I can otherwise.
Since there is little that we can do about re-blooming, the best advice I have is to enjoy the out-of-season blooms. This may result in fewer blooms in the spring, but some fertilizer and good watering practices should help the plant get back on track.