Except for the indoor Hydrangea varieties, most outdoor varieties of Hydrangea can tolerate the harsh days of winter in your garden. Anyway, as I told you in my other post, the soil temperature changes in a pot are faster and more intense in comparison to the ground. Hence you should take precautions to prevent frostbite of your potted Hydrangea roots. I’m a horticultural consultant and listed all you should do in my previous post “Can leave my potted Hydrangea outside in winter?”.
Nevertheless, if you think you should bring your potted Hydrangea inside for winter, you must consider tips to see its stunning flowers next year. You may think about the relationship between transferring your Hydrangea inside and flowering!
As a horticultural consultant with a PhD in Plant Protection science, I know various natural factors are involved in blooming plants. Georges Bernier and Claire Périlleux (2005) discussed them in their article “A physiological overview of the genetics of flowering time control”. For instance, events like vernalization (chilling), moderate temperatures, and short days are necessary for blooming Hydrangea. Elin Fjellvang Nordli et al. (2011) investigate this issue in their article “Temperature and photoperiod control of morphology and flowering time in two greenhouse grown Hydrangea macrophylla cultivars”.
As a result, If you put your potted Hydrangea inside during winter, you may not see any flowers next year. In the following, I discussed the flowering cycle of Hydrangea macrophylla, one of the most popular cultivars of Hydrangeas.
Flowering Cycle of Hydrangea macrophylla and the Importance of Winter in its Blooming
Flower Bud Formation Happens After the Previous Bloom:
Hydrangea macrophylla is unique in forming its flower buds for the next year’s bloom immediately after the current year’s flowering cycle. This is important for understanding how the plant can flower in summer despite certain conditions like moderate temperatures, vernalization, and short-day conditions.
After flowering in summer, the plant begins the process of bud differentiation for the following season’s blooms. The buds are formed on the previous year’s growth, typically in late summer or early fall.
This means that by the time the plant is finished blooming in summer, it has already set the buds for next year’s flowers, and these buds will lie dormant through the colder months.
Vernalization (Chilling):
For the flower buds to successfully develop and bloom the next year, Hydrangea macrophylla requires a chilling period during the winter months. This chilling period typically occurs between 5-10°C, which is why these plants are well-suited to temperate climates that experience cold winters.
The chilling period is essential because it helps break dormancy and prepares the plant for the next flowering cycle. The buds, which were formed after the previous summer’s bloom, “wait” in a dormant state until they receive the cold temperatures of winter.
Once the chilling period is met, the plant begins to “wake up” in spring as temperatures rise, but the flower buds that were formed the year before are already primed to develop and bloom in early to mid-summer.
Moderate Temperatures and Short Days:
After the winter chill, the plant begins to flower in late spring to early summer, once the temperatures have warmed but are still moderate (typically between 15-18°C).
The Hydrangea macrophylla species also has a short-day requirement for flower bud initiation. This means that the plant flowers when the days are shorter, typically in late spring or early summer before the days become long and hot.
Even though summer days might eventually lengthen, early summer still offers the moderate temperatures and shorter days that Hydrangea requires for its flowers to develop properly. This is why you typically see the plants blooming in the warmer months (June to August) in temperate regions.
How the Flowering Cycle Works in Nature?
Late Summer/Early Fall (Post-Bloom Period): After the plant flowers, start to form flower buds for the following year on the previous year’s growth. These buds are small and will remain dormant over the colder months.
Winter (Chilling): The plant undergoes a chilling period, where temperatures stay cool enough to fulfil the vernalization requirement for the buds.
Spring (Bud Development): Once the chilling period is complete, temperatures begin to warm. The plant starts to “wake up” from dormancy and the buds begin to swell in preparation for the next flowering season.
Early to Mid-Summer (Flowering): The buds that formed after the last flowering cycle bloom in summer, typically in late spring to early summer. This flowering typically happens when the temperatures are moderate, and the photoperiod (day length) is still short enough to suit the plant’s flowering needs.
Why Summer Blooming Works Despite the Conditions?
Even though Hydrangea macrophylla needs moderate temperatures, vernalization, and short-day conditions, its flowering cycle is structured in such a way that:
The flower buds are formed after the previous summer’s bloom, during the late summer and fall.
The plant then spends the winter in a dormant state, receiving the necessary chill to break dormancy.
As spring temperatures rise, the already-formed flower buds begin to grow and bloom, reaching their full glory in the following summer, typically around June through August, when the conditions (moderate temperature, shorter days) are ideal for the plant.
Can I Bring My Potted Hydrangea Inside for the Winter?
According I told you above, I recommend: wrapping your pot with burlap, bubble wrap, or old blankets to keep it insulated. You can also add a thick layer of mulch, such as straw or wood chips, on top of the soil to help retain warmth and moisture. Anyway, in harsh days of winter, you can put its pot near a wall or under a porch, to protect it from harsh winds and extreme temperatures or bring inside.
In Conclusion
Hydrangea macrophylla flowers in summer because it forms its flower buds after the previous summer’s bloom (late summer to early fall). These buds undergo a chilling period in winter to break dormancy, and by early to mid-summer, when temperatures are moderate and the day length is still short, the buds bloom. The plant’s cycle of dormancy, chilling, and bud formation aligns perfectly with the natural seasonal changes, allowing it to flower in the warmer months despite its need for cool temperatures and short days. So, if you bring your potted Hydrangea inside in winter, you may prevent its flowering next year. I recommend reading my other post “Difference between indoor and outdoor Hydrangeas“.
Elahe Rabiei
Hi, I’m Elaheh. My Academic major is plant protection, and houseplants are my expertise. As a houseplant lover, my house is full of indoor plants and it is my passion to take care of them. Hence, I’m here to share my knowledge and experience about growing healthy houseplants. I am also a plant protection advisor, so feel free to ask me any questions you may have.