All about hydrangeas

By Jean Henry Published:

Kristine McNiel operates Highland Moor, a family propagation nursery that offers Kentucky native species, popular woody ornamentals, perennials and wildflowers. The nursery’s specialty is hydrangeas and it is the leading producer of hydrangeas for specialty cut stem production and landscape use in the state.

At the May meeting of The Garden Club of Frankfort, McNiel shared growing and landscaping advice about hydrangeas with a presentation of slides representing the amazing range of colors offered in their greenhouse- grown specialty cut-stem hydrangeas.

There are four main categories of hydrangeas are: hydrangea arborescens (the native and “Annabelle” types); hydrangea macrophylla (with big, round, colorful heads); hydrangea paniculata (such as ‘Limelight’); and hydrangea quercifolia (with leaves resembling oak leaves and large flower heads usually cone-shaped).

One of the most common questions asked about hydrangeas is how to control the color of the bloom. Some like them pink, some like them blue and some like them with shades in between. The color is dependent on the amount of aluminum absorbed by the plant from the soil.

In our area the soil pH typically makes aluminum readily available and flowers show blue. Adding lime to lower the pH will make the aluminum less absorbable, and flowers will show pink. If this is attempted it should be done gradually.

Hydrangeas need consistently moist, well-drained soil. They need at least an inch of water a week. Direct watering, such as a drip hose, is most efficient. Hydrangea leaves will wilt if not enough water is provided. Even with sufficient water hydrangeas planted in full sun will wilt during the hottest part of our summer days, but when the temperature cools, leaves should return to normal.

Hydrangeas need fertile soil. Fertilize in late winter or early spring, before leaves show. Slow-release fertilizers are recommended.

Pruning depends on the type of hydrangea and whether you see a need for pruning. The older generations of H. macrophylla only bloom on old wood so there will be a problem of losing blooms the season after pruning. But if it is nevertheless necessary to prune the shrub to control its size it is best done immediately after flowering.

New generations of H. macrophylla (such as the Endless Summer series) bloom both on old wood and new wood. If you prune these you can take them down to 12-18 inches from December to March.
H. quercifolia should be pruned after flowering late summer or fall. H. paniculata can be winter or spring pruned. H. arborescens will have winter injury and will require pruning. It can be pruned back to 12-18 inches during the winter.

The most common mistake in planning to use hydrangeas in the landscape is failing to take into account the mature size of the shrub. Most will attain a size of 3-6 feet in each direction. Some get even larger. It is best to study the plant tag carefully when making your purchase and plan accordingly. They reach mature size quickly.

For sustainable success plant hydrangeas in shady areas such as the north or east sides of buildings, under pine trees, or along wooded areas. The plants will succeed in more exposed areas but will need attention to watering and will show stress during 80-90 degree days.

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