Hydrangeas are popular ornamental shrubs in Illinois landscapes, providing massive blooms throughout the summer. Pruning is necessary maintenance, but the timing depends heavily on the specific species and the regional climate. In Illinois, improper timing can be detrimental because cold winters and late spring frosts can damage or remove flower buds. Knowing your plant’s bloom habit is the single most important factor, as pruning at the wrong moment can eliminate flowering for an entire season.
Understanding Bloom Habit
The success of pruning depends on whether the hydrangea blooms on “old wood” or “new wood.” Old wood refers to stems grown the previous summer. Flower buds are set on these stems in late summer or early fall, survive the winter, and bloom the following year. This group includes Bigleaf (Hydrangea macrophylla), Oakleaf (H. quercifolia), and Climbing (H. anomala) hydrangeas.
New wood refers to fresh growth that emerges in the current season. Flower buds form and bloom on these same stems a few months later. This category is generally hardier and includes Smooth (H. arborescens), such as ‘Annabelle’, and Panicle (H. paniculata), like ‘Limelight’. New wood bloomers can be pruned heavily during the dormant season without sacrificing flowers. If you are unsure of the type, early summer flowers often indicate an old wood bloomer, while mid-to-late summer blooms suggest new wood.
Pruning Schedules for Old Wood Bloomers
Pruning species that bloom on old wood, such as Bigleaf and Oakleaf hydrangeas, requires precise timing to avoid removing next year’s flower buds. The safest window for cutting is immediately after the flowers fade in summer, typically between late June and late July in Illinois. This timing allows the plant enough time to develop new growth and set flower buds before the first hard frost arrives.
Pruning should be limited to shaping and deadheading (removing spent flowers). Any structural pruning, such as removing old or weak canes, must be completed no later than mid-to-late August. Cutting back wood later encourages tender new growth highly susceptible to winter damage, which kills developing flower buds. For these sensitive types, removing more than one-third of the plant’s total mass is not recommended.
Pruning Schedules for New Wood Bloomers
New wood bloomers, including Panicle and Smooth hydrangeas, are more forgiving and tolerate aggressive pruning. Since they form flower buds on the current season’s growth, the ideal time for cutting is during the dormant season. This window typically falls in late winter or early spring, generally from late February through early April, before new growth emerges.
These hydrangeas can be pruned aggressively. Panicle types often respond well to removing about one-third of the old growth to maintain shape and encourage stronger stems. Smooth hydrangeas, such as ‘Annabelle,’ can be cut back hard, sometimes down to one foot above the ground. This rejuvenation pruning prevents the mature plant from flopping under the weight of its large blooms and ensures the plant produces vigorous new stems that will support the season’s flowers.
Managing Cold Weather Damage and Maintenance Cuts
In Illinois, the harsh winter climate often requires corrective pruning to manage cold damage. Wait until the plant actively begins to leaf out in late spring to determine the full extent of winter-killed wood. Any branches that are brittle or fail to show green growth when scraped should be cut back to a healthy bud or to the ground.
Removing dead, damaged, or diseased wood can be safely done at any time of year without risking the next season’s blooms, as this is a maintenance cut necessary for plant health. Deadheading (removing spent flower heads) is a separate maintenance task from structural pruning. This can be performed throughout the summer to tidy the plant’s appearance, or the dried blooms can be left on the plant for visual interest and minor winter protection.