Hydrangeas are popular flowering shrubs, and Missouri gardeners often wonder when their plants will bloom. The timing is not uniform across all varieties; it is linked to the specific species, the local microclimate, and the plant’s growth habit. Understanding these factors helps predict the bloom season for hydrangeas grown throughout the state.
General Bloom Timeline in Missouri
Hydrangea flowering in Missouri typically begins in late May or early June and continues until the first hard frost, usually in late September or October. A garden featuring multiple varieties can enjoy continuous color throughout the summer and into autumn. The exact start date for any individual shrub depends on the species and the year’s weather patterns. A warm spring accelerates the timeline, while a late frost can delay or eliminate the first flush of flowers.
Understanding Bloom Timing by Hydrangea Type
The primary factor determining when a hydrangea blooms is whether it flowers on “old wood” or “new wood.” Old wood bloomers, such as Bigleaf (Hydrangea macrophylla) and Oakleaf (Hydrangea quercifolia), set their flower buds on the previous season’s growth, meaning the buds are present on the stems all winter. These varieties are the earliest to bloom, typically starting in June and continuing into July. Cutting these stems back in spring removes the developing flower buds, resulting in no blooms that year.
New wood bloomers produce their flower buds on the current season’s growth, which emerges in the spring. This group includes Smooth (Hydrangea arborescens), like ‘Annabelle’, and Panicle (Hydrangea paniculata), such as ‘Limelight’. Since they need time to grow new stems and form buds, these types bloom later, generally starting in July and lasting through August and September. Panicle hydrangeas often continue to display color, with blooms changing from white or green to pink or red as autumn approaches.
Pruning and Winter Care for Reliable Blooms
Improper pruning often causes hydrangeas to fail to bloom on schedule. Pruning an old wood bloomer, like a Bigleaf hydrangea, in late winter or early spring removes the flower buds set the previous fall, eliminating potential early summer flowers. For these varieties, pruning should be limited to removing dead wood in early spring, or light shaping immediately after the flowers fade in summer.
New wood bloomers, including Smooth and Panicle types, are more forgiving and can be pruned back hard in late winter or early spring without sacrificing the summer bloom. This timing encourages the vigorous new growth on which the flowers will form. In Missouri’s fluctuating climate (USDA Zones 6 and 7), winter care is important for old wood bloomers. Protecting the sensitive overwintering flower buds of Bigleaf hydrangeas with burlap or mulch prevents them from being killed by extreme temperatures, ensuring they are intact for the early summer bloom.
Troubleshooting Delayed or Absent Blooms
If a hydrangea misses its established bloom window, the cause is often an environmental factor separate from pruning or winter damage. Insufficient sunlight is a common cause, as hydrangeas require at least four hours of direct sun daily for flower production. Plants in deep shade may produce healthy foliage but lack the resources to form flower buds, leading to an absence of color.
Incorrect fertilization can also suppress flowering, particularly if the product is too high in nitrogen. High-nitrogen fertilizer encourages the plant to focus energy on producing lush leaves and stems at the expense of developing blooms. Hydrangeas are moisture-loving plants, and prolonged drought stress causes the plant to prioritize survival over flower formation. Consistent, deep watering supports the plant’s energy needs throughout the growing season and promotes timely, abundant flowering.