Both oakleaf and smooth hydrangeas evolved in and along the woodland landscape. They prefer moisture-retentive, slightly acidic soil high in organic matter. They perform well in full sun. Both species offer full-size and dwarf sizes.

Both species prefer morning sun and afternoon shade but can tolerate a southern or western exposure if planted under a higher canopy of trees. Expect full bloom by June. Blooms will last (but change color as they age) into fall. There the commonalities end!

Appearance

Arborescens produce round mopheads and lacecaps. Emerging in shades of lime green, they mature to white and hold their color if well-watered through the summer. Some recent cultivars, e.g., Incrediball® Blush will bloom as a light pink. Leaves are oval-shaped. Dwarf sizes are available.

The cone-like spires of the oakleaf typically emerge white and, depending on the cultivar, mature from white to green to brown or white to pink to chocolate brown. Regular watering is crucial to experience the color change. Drought conditions will age the blossoms prematurely, skipping the beautiful transitions. Oakleafs' deeply-lobed leaves offer spectacular fall color well into winter.

H. Arborescens "Haas Halo" Photo: Michele Walfred

Species Spotlight

Concluding a five-year study of native hydrangeas and pollinator preference, the Mt. Cuba Center in Hockessin Delaware announced a clear winner: "Haas Halo." An H. arborescens species, this lacecap attracted more pollinators than their mophead counterparts (Mt. Cuba/September/2021).

Bees visited "Haas Halo" while their nearby mophead counterparts were ignored.

The creamy white centers of this lacecap are rich in pollen compared to the sterile white florets that surround the bloom head.

Pruning

Here treatment of our two native species differ! Oakleafs do not need to be pruned. If size is an issue, selective or corrective pruning is recommended only after blooming in late July. Oakleafs bloom on old wood and set their blooms for next year in late summer and early fall. Pruning any other time will remove future blossoms. Arborescens on the other hand, bloom on new wood, and heavy pruning is recommended.

In Delaware, late winter or early spring, e.g., March 15 is ideal. Prune out narrow twigs and allow more vigorous canes to remain. However, the entire shrub can be taken down by two-thirds to encourage more blooms. Because this species blooms on new wood, it is winter hardy, and spring-forming buds are normally unaffected or damaged by cold winters.

Purchasing and Site Selection

Before purchasing any shrub or tree, obtain a soil test to determine whether your soil needs amendments. New cultivars are introduced annually, so read the label carefully. As their name suggests, hydrangeas are heavy water users and prefer soil that retains moisture but drains well.

They should be sheltered from high sun and high heat locations. All varieties of hydrangeas are hardy for Delaware's Zones 7a and 7b and 8a.. Arborescens grow well among other shrubs. Arborescens are not considered a stand-alone specimen plant, while Quercifolia make excellent specimen shrubs.

12 photos of hydrangeas by Michele Walfred. From left to right, Oakleaf: "Snow Queen" planted under a dogwood tree, Oakleaf: Honeybee visits "Ruby Slippers", Oakleaf: A young "Alice" has large blooms and leaves, Oakleaf: Splendid fall color on lobed leaves, Oakleaf: Bee exploring "Snow Queen", Oakleaf: A swallowtail visits an aging "Snow Queen", Oakleaf: Blossoms of "Snow Queen" change colors as they age, Oakleaf: A chocolate brown flower of a fully-aged oakleaf adds fall and winter interest, Smooth Hydrangeas: Incrediball ® is a larger version of the well-known Annabelle, Smooth Hydrangeas: Large blossoms of Incrediball®, Smooth Hydrangeas: Young"Haas Halo" lacecap, Smooth Hydrangeas: Arborescens can weep from weight, drought or heavy rain

Issues and Problems

Native shrubs are typically less vulnerable to common hydrangea diseases such as Botrytis Blight, Cercospora Leaf Spot, and Powdery Mildew. Of these, in Delaware's hot and humid climate, Cercospora Leaf Spot is most common. Disease presence can be mitigated by watering the shrub from the bottom and keeping the leaf surface dry. Avoid automatic or overhead sprinkler irrigation. Affected leaves should be removed and destroyed and fallen leaves raked away and disposed of (not composted). Leaf Spot will not affect the health of the bloom or shrub overall but is unsightly! Excessive heat regardless of water uptake will cause wilting in all hydrangeas. A cooler, woodland environment surrounded by mature trees is best for these beautiful native shrubs.

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