Hydrangeas are popular garden shrubs known for their large blooms and naturally high water requirements. During the spring and summer growing season, the plant’s lush foliage demands a consistent supply of moisture to prevent wilting. This regular hydration supports plant health and the development of next season’s flower buds. However, as the weather changes, continuing the summer watering regimen can be detrimental to the plant’s preparation for the cold months.
Identifying the End of the Growing Season
The signal to change watering habits is not tied to a specific date but rather to environmental and plant cues. Shorter day lengths and cooling temperatures in late summer and early fall trigger a physiological slowdown. This natural process prepares the plant for winter dormancy, a phase of rest and survival.
Visual indicators show the active growing season is concluding. Summer blooms will begin to fade, dry out, and take on a papery texture. Simultaneously, the stems of deciduous varieties will start to harden, becoming less flexible to withstand winter conditions.
The leaves may also begin to change color, transitioning from deep green to hues of yellow, red, or bronze, particularly in Hydrangea quercifolia (oakleaf hydrangea). This shift indicates the plant is reducing photosynthetic activity and pulling energy back into its stems and roots. Depending on the local climate, these cues typically appear between late August and early October, signaling the time to transition away from summer watering.
Gradual Reduction and Tapering Off
The question of “when to stop watering” is better framed as “when to begin a gradual reduction.” Abruptly ceasing water can stress the plant. Continuing heavy watering encourages soft, new growth highly vulnerable to early frost damage. The goal is to slowly reduce the water supply to encourage the hardening-off process necessary for dormancy.
This tapering process should begin once the first signs of seasonal change are noted, ideally four to six weeks before the area’s average first hard frost. Start by reducing the frequency of deep watering, allowing the soil to dry out more between applications. If watering twice a week during summer, reduce this to once every seven to ten days.
Monitoring soil moisture is the best guide during this transition. Before watering, check the soil by inserting a finger a few inches deep; the top two to three inches should feel dry. When you water, provide a lighter application than the deep soakings of summer. This ensures the roots receive just enough moisture without encouraging a flush of late-season growth, helping the plant conserve energy for the coming cold.
Hydrangea Needs During Dormancy
While the tapering process ends, ground-planted hydrangeas should not be left completely dry. The final step before the ground freezes is a deep, thorough watering to saturate the root zone. A well-hydrated root system heading into winter is more resistant to desiccation, a common cause of winter damage, especially from drying winds.
In regions where the ground does not freeze solid or where winter has prolonged dry spells, maintenance watering may still be necessary. A deep, infrequent application of water, perhaps once a month, is beneficial until consistent winter precipitation returns. This is particularly important for evergreen varieties, such as Hydrangea quercifolia, and hydrangeas grown in containers, as pot soil dries out faster than garden soil.
For potted hydrangeas moved into an unheated garage or shed, the roots remain exposed to air and are prone to drying out. These plants require a small amount of water about once per month to keep the roots moist but not wet. The goal during dormancy is simply to prevent the roots from becoming desiccated before the spring thaw.