Oakleaf hydrangea, or oak hydrangea, delights with its namesake oak-leaf shaped leaves and white flowers. We will show you what to consider when planting and caring for this type of hydrangea.
The oak-leaved hydrangea is a special eye-catcher in the garden with its lush flower panicles and characteristic oak-leaf shaped foliage. The decorative leaves, reminiscent in shape of those of the American red oak, take on a pretty colour in autumn.
Oakleaf hydrangea: origin, characteristics and flowering period
Oakleaf hydrangea (Hydrangea quercifolia), also called oak hydrangea, is a species in the hydrangea family (Hydrangeaceae). Originally from the southeastern United States, it thrives there in dry forests and steppes.
Oakleaf hydrangea grows as an upright shrub about 1 to 2 m tall. It also grows to about 1 to 2 m wide, sometimes even wider when older due to runner formation. Its flowers open between July and September, arranged in conical to roundish panicles about 15 cm tall. They are composed of sterile false flowers and fertile flowers. The false flowers usually have 4 to 5 petals and are 3 to 4 cm in size. At the beginning of flowering they are pure white, later they turn reddish. The fertile flowers are close together between the false flowers and are less conspicuous. While the sterile flowers serve to attract insects, it is the fertile flowers that provide pollinators with pollen and nectar.
The distinctive feature of the oak-leaved hydrangea, which also gives it its name, is the striking shape of its leaves. The leaves, 10 to 20 cm long and about 15 cm wide, are pinnately lobed and strongly resemble the foliage of American red oak (Quercus rubra), especially since they also turn red, dark red, or even purple in autumn. In summer, the semi-evergreen foliage is deep green on top and gray-green on the underside. The upper side is wrinkled while the underside has felt-like hairs. The shoots also initially have a reddish felt, but this recedes with age.
The most beautiful cultivars
Cultivars of oakleaf hydrangea differ in flower structure, autumn colouring or even growth height. The following cultivars are extremely ornamental and will particularly enrich your garden:
The cultivar Hydrangea quercifolia ‘Alice’ grows 1.5 to 1.8 m tall and 0.5 to 1 m wide. It forms lush white and later pale pink flower panicles in large numbers. The foliage initially appears a vibrant green and contrasts beautifully with the white glowing flowers. Later, the leaves take on a pretty autumn colour.
The variety ‘Snowflake’ forms double pseudo flowers and is thus a special eye-catcher. It grows 0.8 to 1.5 m high and 0.6 to 1.2 m wide. The large, oak leaf-shaped leaves turn reddish to bronze in autumn.
The cultivar ‘Ruby Slippers®’ has a somewhat more compact growth. It reaches a height of growth of 1 to 1.5 m. Its flower panicles first take on a pinkish colour and later a dark red colour as they bloom.
Growing oakleaf hydrangeas: when and where
Oakleaf hydrangeas can be planted throughout the year. It is essential, however, that no frost is expected on the days around the planting.
The hydrangeas prefer a sunny to semi-shady location in the garden or on the balcony, sheltered from the wind. The soil should be fresh to moist, and humus. On sites that are too nutrient-rich, shoots will mature at a reduced rate before frost, so they may be affected more frequently by frost damage. So large gifts of fresh compost before planting are not appropriate for oakleaf hydrangea.
Oakleaf hydrangea is sensitive to waterlogging, so in case of compacted or very heavy soil, a drainage layer, for example, of gravel, should be introduced. When planting in pots, such a layer is also absolutely necessary.
Compared to other hydrangea species that are very sensitive to high levels of lime in the soil, oakleaf hydrangea is lime tolerant. The soil pH may also be slightly higher for oak hydrangeas than for bigleaf hydrangeas, for example. It should be in the neutral to slightly acidic range. Nevertheless, the oak-leaved hydrangea is also lime-loving, and therefore should not be limed in any case.
When you find the right place, you can plant the oak-leaved hydrangea. Dig a sufficiently large planting hole in the flower bed. It should be about twice the size of the root ball. If the soil in your garden does not meet the above requirements, you can mix it with sand to one-third to increase substrate permeability, as well as mix in mature compost. Alternatively, you can buy a peat-free potting soil and mix it with sand in the above ratio to get the optimal substrate. For this purpose, for example, our Plantura Organic All Purpose Compost is ideal – it contains all the important nutrients in a balanced ratio. With a pH value of 6.1 to 6.9, it lies in the slightly acidic to neutral range making it suitable for the oakleaf hydrangea.
Put a small portion of the substrate back into the planting hole and place the planting ball in the centre. By loosening the root ball a little with your hands or with the help of a spade, you inflict small injuries on the roots, which stimulates their growth and branching. Then, the planting hole is completely filled with substrate, the soil is pressed and generously watered. If you want to plant several hydrangeas next to each other at once, you should keep a planting distance of about 2 meters.
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Tip: Freshly planted hydrangeas benefit greatly from a watering border, which they can easily sculpt from excess soil after planting. This is regularly filled with water and prevents irrigation water from running away unused.
Oakleaf hydrangea is also suitable as a pot plant for the balcony or terrace. Choose a sufficiently large planter with a drainage hole so that excess water can run off when watering and no waterlogging can occur. To avoid the formation of waterlogging, clay shards should be placed on the bottom of the vessel.
Hydrangea quercifolia care
As with all hydrangea species, a good water supply is a basic requirement for the successful development of hydrangea plants. Especially young plants need daily watering. However, apart from occasional applications of fertilizer and maintenance pruning, no special care is required.
Watering and fertilising
Newly planted hydrangeas need daily watering to grow well. During dry, hot periods of summer, you should also water oakleaf hydrangeas once a day, and in pots, perhaps twice a day. Even though oak hydrangeas are more tolerant of lime than other Hydrangea species, you should prefer to use low-lime rainwater. Oakleaf hydrangeas love a cool, moist soil. This is most easily achieved by a mulch layer of leaves or bark mulch. Such an overlay serves as an evaporation barrier and keeps moisture in the soil longer.
Tip: Water your hydrangeas in the morning and/or evening, when the sun is not yet shining so strongly, so that the water is used efficiently and does not evaporate immediately.
Hydrangeas in pots, in particular, should be fertilised annually, and preferably in the spring, so that they can start the growing season well. For this purpose, our Plantura Hydrangea Food is ideal. With its slow-release effect, it reliably supplies your hydrangeas with all the necessary nutrients and prevents typical deficiency symptoms and diseases. Work the fertiliser in shallowly and, if necessary, cover it with an additional mulch layer of leaves or the like so that it begins to work quickly.
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Tip: Fertilising too late makes plants susceptible to frost, because it inhibits the maturation or hardening of the shoots at the end of the growing season. Therefore, it is recommended to fertilise the last time in May-June.
Pruning oakleaf hydrangeas
Oakleaf hydrangeas have a beautiful, upright growth habit. They can be pruned if necessary, but even without pruning the plants develop beautifully. Only the shoots and flower panicles that froze or dried up over the winter should be removed in the spring. Cut off the withered flowers with clean secateurs just above the new flower buds.
Oakleaf hydrangeas are hardy in our part of the world. When buying it is best to choose well-hardened plants from specialized stores. Often plants from nurseries are preferable to those from garden centres. Well hardened hydrangeas can withstand temperatures as low as -23 °C, provided that they do not stand in the cold and damp winter wind. Young shoots also survive temperatures down to -10 °C without damage. If you still want to play it safe, you can cover the soil around the base of the hydrangea plant with leaves or fir branches. In this way, their roots are not damaged by frost.
Hydrangeas in pots are somewhat more vulnerable due to the small volume of soil: It may happen that the entire pot freezes through. Therefore, in late autumn, you should wrap the planter with plant fleece or jute bags and, if necessary, place it in a sheltered place, such as a house wall.
Propagating oakleaf hydrangea
Oakleaf hydrangea can be propagated by cuttings. These need to be taken in early summer. Cut one-year-old flowerless shoots from the plant and divide them into pieces about 10 to 15 cm long. The leaves are then removed except for the upper pair of leaves and the cuttings are placed at least 5 cm deep in planters filled with sowing soil. For this purpose, for example, our nutrient-poor Plantura Organic Herb & Seedling Compost is suitable, which mixed with at least one-third sand forms the right substrate for the cuttings. The substrate should be moistened daily. In a bright place without direct sunlight and at a temperature of about 15 °C, the cuttings can take root and grow into new hydrangea seedlings.
If you would like to learn about other hydrangea species, you can learn all about the Hydrangea paniculata in our dedicated article.