Cultivating Heavenly Hydrangeas
Hydrangea is a genus of approximately 75 species of flowering plants which are native to the temperate parts of Asia and the Americas. The name is derived from the Greek words hydor meaning water and angeion meaning vessel, a reference to the plant’s seed pods, which look like small water jugs.
Interestingly, hydrangeas can be deciduous or evergreen shrubs, climbers, and even small trees. The common cultivated varieties of hydrangeas have prolific, showy flowers, which usually comprise both small fertile and larger, showy sterile florets. They typically bloom from early summer through autumn; old blooms often develop distinct autumn colours.
Hydrangeas are excellent for a wide variety of gardening sites from shrub borders and garden arches to containers and group plantings. Importantly, most hydrangeas are easy to cultivate, tolerate almost any soil, and produce loads of blooms.
Types of Hydrangeas
Before getting to cultivation tips and tricks, we want to touch upon the five main types of hydrangeas.
Hydrangea macrophylla (bigleaf or French hydrangea) is the most common type of hydrangea in the United States and Western Europe. There are three most popular types of bigleaf hydrangea: mophead, lacecap, and mountain.
Bigleaf hydrangeas have large flower heads that are typically, blue, pink or purple. Lacecaps are virtually identical to mopheads except the shape of their blooms. The small florets in the centre of the lacecap are the fertile flowers, and the large showy florets around the outer edge are the sterile flowers.
The leaves of mophead and lacecap hydrangeas are often heart-shaped with coarsely toothed edges. Generally, leaves are approximately 10 to 15 cm long (4 to 6 inches) and 7.5 to 13 cm wide (3 to 5 inches). Mountain hydrangeas resemble lacecap hydrangeas; however they tend to be more cold hardy (USDA hardiness zone 5 rating).
Hydrangea arborescens (smooth or wild hydrangea) is native to the United States and is much more resilient to hot climates than other types of hydrangeas. It is also cold hardy to USDA hardiness zone 4.
The smooth flower heads of Hydrangea arborescens can grow as big as 30 cm in diameter (12 inches). These shrubs are often grown as hedges because of their large size. Their leaves are generally heart-shaped, but thinner than those of the macrophylla.
Hydrangea paniculata (panicle hydrangea) have cone-shaped flower heads. These are the most cold hardy hydrangea and can grow in USDA hardiness zones 3 to 7.
The leaves of panicle hydrangeas tend to be smaller and thinner than those of bigleaf hydrangeas; typically 7.5 to 15 cm long (3 to 6 inches) and 7.5 to 10 cm wide (3 to 4 inches). Leaf edges differ by the variety of panicle hydrangea; some are finely toothed while others are more coursely toothed.
In addition, panicle hydrangeas have three leaves growing from a stem node and are arranged in a whorl around the node. Panicle is the only type of hydrangea that can be pruned into a tree form; the central stems develop into nice trunks.
Hydrangea quercifolia (oakleaf hydrangea) are easy to identify due to their leaves which resemble those of the red oak. Leaves of different oakleaf varieties range in size from about 10 X 10 cm (4 X 4 inches) up to a whopping 25.4 X 25.4 cm (10 X 10 inches). The oakleaf is also the only type of hydrangea whose foliage changes colour in the autumn; changing from green to shades of bronze, red, and purple.
Hydrangea petiolaris (climbing hydrangea or Japanese vine hydrangea) is a slow-growing vine form of hydrangea that is native to parts of Asia. Although a slow grower, it can eventually climb to heights of nearly 24 metres (80 feet) and can grow in USDA zones 4 to 8.
The flowers of the petiolaris are usually white and often have a sweet fragrance.
How to Successfully Cultivate Hydrangeas
Now, onto tips and tricks for growing hydrangeas. If you follow some simple general guidelines, it is easy to successfully cultivate these lovely plants.
Where to Plant:
- Soil type: hydrangeas are quite adaptable and can grow in virtually any type of soil. However, most thrive in rich, porous, moist soils, so add compost to enrich poor soil.
- Soil pH: neutral to slightly alkaline or slightly acidic to neutral. However, the flowers of bigleaf hydrangeas change colour based on the soil pH. Blues are best grown in acidic soil; pinks and reds do best in alkaline or neutral soil (more detail provided below).
- Sun: generally, hydrangeas prefer full sun in the morning, with afternoon shade; however, many grow and bloom well in partial shade.
When and How to Plant:
- When: plant hydrangeas in autumn or spring.
- How: dig a hole as deep as the root ball and 2 to 3 times as wide. Set the plant in the centre of the hole and fill it half full with soil. Now, thoroughly water the plant. After the water has drained, fill the rest of the hole with soil.
- Spacing: space multiple hydrangeas about 0.9 to 3 metres apart (3 to 10 feet).
General Care:
- Watering. For the first couple of years after planting and during periods of drought, be certain to regularly water hydrangeas. The leaves act as a good barometer for dryness and wilt when the soil is too dry.
- Fertilising. If your soil is rich in humus, you may not need to fertilise your hydrangeas. For light or sandy soil, it’s best to feed the plants once a year in late winter or spring. However, be careful as too much fertiliser encourages leafy growth at the expense of blooms. If your hydrangea isn’t flowering, you may also be pruning it too hard or at the wrong time (more on pruning below).
- Winter care (needed in areas prone to killing frosts and snow). In the late autumn, cover the plants with a “cage” using chicken wire and loosely fill the cages with pine needles, leaves, or straw. (Maple leaves are not recommended as they tend to mat when wet and could suffocate the plant.)
- Pruning. Most hydrangeas bloom on the previous year’s growth. So, unless absolutely necessary to rehabilitate a neglected or poorly plant, we do not advise cutting hydrangeas to the ground as this will remove all flowers for that summer. Selective pruning is best done in late winter or early spring, which will encourage new growth and more prolific blooming in future years. It is also an opportune time to remove dead or cold damaged branches. Here are some specific pruning tips for the different types of hydrangeas.
- In mild areas, bigleaf and oakleaf hydrangeas can be dead-headed as soon as the blooms start to fade in summer.
- Climbing hydrangea should have the odd, overgrown shoots cut back immediately after flowering. If rehabilitating an established, overgrown climber, we recommend selective hard pruning over several years to avoid a number of flowerless summers.
- Panicle and smooth hydrangeas tend to flower more prolifically when pruned annually to a framework of branches. Therefore, in the spring cut back last year’s stems to a pair of healthy buds to maintain a permanent framework.
Changing the Colour of Hydrangea Flowers:
It is possible to change the flower colour of some hydrangea species; but it may take weeks or even months to happen. For instance, the flower colour of some mophead and lacecap hydrangeas (H. macrophylla) change colour based on the soil pH. Acidic soils with a pH of less than 5.5 tend to produce blue flowers, while soils with a pH greater than 5.5 tend to produce pink flowers. Generally, white flowers are not affected by soil pH. Also, be aware it’s easier to change blue flowers to pink than pink flowers to blue.
We think it’s best to accept the colour of the hydrangea you choose. Nonetheless, if you really wish to change the colour of your hydrangea, we advise waiting several years after planting to ensure the plant has fully recovered after the shock of planting.
You should first conduct a soil test to determine your soil’s current pH. You can purchase a soil testing instrument at many garden centres or some garden centres will test a soil sample for you. To raise the pH of acidic soils, liming materials will do the trick. Elemental sulfur, aluminum sulfate, iron sulfate, or acidifying nitrogen will lower the soil’s pH. It’s important to follow the instructions given for the particular product you select.
A Few of My Favourite Hydrangeas
Hydrangea macrophylla ‘Veitchii’ is a compact, bushy deciduous shrub with glossy leaves and lacecap flowerheads with small purple-blue fertile flowers surrounded by large white sterile florets, which mature to pink. ‘Veitchii’ is a great choice for a mixed border with other hydrangea and makes a great cut flower.
The distinctive lime green coloured cone-shaped flowers of the Hydrangea paniculata ‘Limelight’ are stunning. The dense sterile florets open a beautiful lime green and slowly fade to creamy white before turning shades of deep pink in the autumn. They make ideal cut flowers – both fresh and dried.
The autumn flower colour of the Hydrangea paniculata Vanille Fraise ‘Renhy’ sets it apart from other hydrangeas. The large, pyramid-like flower panicles open in mid-summer a creamy-white colour and slowly turn shades of pink before turning rich pink tones by mid-autumn. Pure. Perfection.
Hydrangea quercifolia, the oakleaf hydrangea, is hands down my absolute favourite type of hydrangea. The oakleaf puts on two big shows annually. The summer show of pure white conical flowerheads is followed by the autumn show of its oak-like foliage that turns lovely shades of bronze, red, and purple. A real show stopper.
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