Voluptuous hydrangeas are part and parcel of South African gardens

Mophead & Lacecap Hydrangeas growing near the sea. Image by Dave Noonan from PixabayMophead & Lacecap Hydrangeas growing near the sea. Image by Dave Noonan from PixabayFrom November through to late summer hydrangeas grace our gardens, and are favourite Christmas flowers. From compact new varieties to the statuesque older ones, there is a perfect hydrangea for every garden. Find  all you need to know about growing them below.

For a very long time it was believed that hydrangeas originated in Japan because by far the greatest diversity of species occur in eastern Asia, notably China, Korea, and Japan. Today we know that hydrangeas are native to both Asia and the Americas, and the discovery of a fossil species called “Hydrangea alaskana” greatly excited the scientific community, as it was recovered from a section of rock at Jaw Mountain in Alaska, USA, and dated from 66 million to 23 million years ago to the paleogene period. Fossils have also recently been discovered in Asia, the continent with which Hydrangeas are still the most strongly associated, and where it is recorded that the Japanese people first started cultivating the various species, thousands of years ago.

It is said that Hydrangeas didn’t appear in Europe until 1736, when a colonist brought a North American varietal to England, and Asian varieties first made their way to Europe in 1775, when Swedish naturalist Carl Peter Thunberg, upon returning from a trip to Asia, brought five plants back to the continent, and ever since hydrangeas have remained a mainstay in gardens across the Northern Hemisphere, where they are well suited to the cool and wet climate.

Today there are around 70 to 75 known species of Hydrangeas, and over 600 named cultivars, which can be deciduous or evergreen, depending on the species, though the widely cultivated temperate species are all deciduous. Most Hydrangea species are shrubs, growing 1 to 2m tall with an equal or greater spread, but some grow into small trees about 3m tall, and others are creeping lianas that can climb up to 30m via tall trees.

The most common species grown in South African gardens are Hydrangea macrophylla, Hydrangea arborescens, Hydrangea paniculata, Hydrangea serrata and Hydrangea quercifolia.

Hydrangea Kamakuru The Bright Moon Of Flowers Image by veronica111886 from PixabayHydrangea Kamakuru The Bright Moon Of Flowers Image by veronica111886 from PixabayBigleaf Hydrangeas (Hydrangea macrophylla)

Hydrangea macrophylla is a deciduous species of hydrangea which comes from the coastal regions of the Japanese islands, as well as the mountainous regions of Japan, from Honshu southwards.  And because this lovely plant with its large green leaves and balls of elegant blooms grew so abundantly and was beloved by the people, it was cultivated extensively in Japanese gardens, and when new ‘sports’, which were called “lacecap” mutations were discovered, the Japanese introduced these new hybrids with their lovely flat and lacy-looking flower heads to gardeners worldwide.

Bigleaf hydrangeas became extremely popular, and in climates where they thrived they escaped garden cultivation and naturalised themselves. Today they are naturalized n China, New Zealand and the Americas, and listed as an invasive species in the Azores and Madeira archipelagos.

Bigleaf Hydrangeas are also called “French Hydrangeas”, “Florist's Hydrangeas, and “Hortensias” and remain a firm favourite with gardeners around the world. The plants bloom from November through to late summer in South Africa, and the flowers come in an amazing range of colours, including intense red, varying shades of blue and pink, and whites, which are often delightfully tinged with green.

The large growing specimens can take 6 to 10 years to reach full maturity, but once mature they are magnificent in stature, and can reach a height of 2m or more, and a glorious spread of at least 2.5m. Innumerable hybrids have been bred for the home garden, and these newer types are much more compact growing, and will often bloom all season, from spring to autumn, and many will also keep their colour no matter the pH of the soil. These compact hybrids don’t occupy as much space, making them great for smaller gardens and pot culture.

Bigleaf Hydrangeas occur in two forms called the “mophead hydrangea”, and the “lacecap hydrangea” (Hydrangea macrophylla normalis). Lacecaps are identical to mopheads in every way except for the shape of their blooms. Mopheads form large pom-pom shaped balls of flowers, while the lacecaps are round and flat. 

On the older varieties the bracts around the blossoms can be white, or shades of pink, blue, or purple, depending on a pH-dependent mobilization and uptake of aluminium from the soil into the plants. Newer cultivars come in colours ranging from cool blues and purples, pinks, sultry rose and shimmering reds, to crisp whites.

Hydrangea Lacecap 'Pink' Image by Jason Goh from PixabayHydrangea Lacecap 'Pink' Image by Jason Goh from PixabayMopheads and lacecaps have identical leaf forms, and in general the leaves are relatively thick and crisp, somewhat shiny, and often heart-shaped. Their edges are coarsely toothed, and they are approximately 10 to 15cm long and 7 to 13 cm wide, but in some cases, they may grow even larger.

Look out for these stunning varieties at your local garden centre:

The Hydrangea “Endless Summer Collection” is the world’s 1st re-blooming mophead hydrangea, which became an instant hit in the gardening world, and remains a best seller for good reasons. This Hydrangea flowers on new and current old wood, and if the dead blooms are continually removed and it is watered and fed regularly, the plants can flower from the beginning from October right through to the end of April.

The Endless Summer Collection comes in lovely shades of blue, pink, and white, and includes lacecapped types. Look out for Endless Summer ‘Blue’, Endless Summer ‘Pink’, and Endless Summer ‘Blushing Bride’ with its radiant, pure white, semi-double flowers that matures to a sweet pink blush.

The Endless Summer Collection produces strong sturdy branches making it a perfect flower for floral arrangements and its full yet compact growth habit makes it perfect for small gardens and a wonderful candidate for pot culture.

Hydrangea macrophylla ‘Nikko Blue’ is an easy to grow mophead, which produces bright blue flowers in acidic soil, and in alkaline soil the flowers are lilac to light pink.

Hydrangea macrophylla ‘Lady in Red’ is a white lacecap with flowers that mature to a deep red towards the end of summer.

Hydrangea macrophylla ‘Sweet Dreams’ is a soft pink lacecap that flowers with abandon and which makes a very good cut flower.

Mountain Hydrangea (Hydrangea macrophylla ssp. serrata)

This exceptional hydrangea is native to mountainous regions of Korea and Japan, and another one of its common names is “Tea of Heaven”, as the leaves of mountain hydrangea contain phyllodulcin, a natural sweetener, and are used to make regionally popular herbal teas, called “sugukcha” in Korea, and “amacha” in Japan, where it is used in the celebration of Buddha's birth.

It is similar to the mophead, except it is a smaller more compact shrub with smaller flowers and leaves, but nonetheless absolutely stunning with its rounded habit, and most attractive dark green, serrated leaves up to 15cm long. From mid to late summer it produces its clusters of blue or pink flower heads, depending on soil pH. And, although it will grow in full sun if the soil is kept consistently moist, it does love semi-shade, especially in hotter gardens.

Numerous cultivars have been selected for garden use, many of which have gained the Royal Horticultural Society's Award of Garden Merit.

Hydrangea paniculata Image by DUOTONE from PixabayHydrangea paniculata Image by DUOTONE from PixabayPanicle Hydrangeas (Hydrangea paniculata)

The panicle hydrangea is native to southern and eastern China, Korea, Japan and Russia, growing in sparse forests, in valley thickets, or on mountain slopes, where it grows as a deciduous shrub or small tree, varying in height and spread from about 1 to 5m tall, with a spread up to 2.5m. In late summer the large panicles of creamy-white flower heads, shaped like plump ice-cream cones appear, and the blossoms will often fade to a pleasing pink colour over time.

Panicle hydrangeas will form lovely small trees in the garden if their central stem, or several stems, are selected and trained to form a framework of trunks and supporting branches. These giants of the hydrangea genus can mature to heights of 3m or more, with an even greater spread. The leaves are relatively easy to identify when compared with other hydrangeas because they are medium green with a matt finish, and smaller, thinner and rougher than leaves of the mophead hydrangea. The edges are finely toothed in some varieties and more coarsely in others.

All the paniculatas will take shade or full sun, and they are known to be very cold hardy, but also do well in warmer more humid climates. Because panicle varieties bloom solely on new wood, they should be pruned back in winter, or immediately after flowering. And unlike mopheads, they’re not picky about soil pH.

Hydrangea paniculata ‘Quickfire’ PBR (Proven Winner) is an early bloomer, flowering from early summer until autumn. The flowers start out white and change to red and pink during the flowering season. This variety is very hardy and will tolerate full sun and occasional periods without water.

Hydrangea arborescens 'Annabella' Image by HeungSoon from PixabayHydrangea arborescens 'Annabella' Image by HeungSoon from PixabaySmooth Hydrangea (Hydrangea arborescens)

The smooth hydrangea is a small to medium-sized shrub up to 3m tall, and is native to the eastern United States. It also sometimes referred to as the “Wild Hydrangea” because it bears cream-colored blooms which fade to an intriguing green over time. It is also called “Sevenbark” due to the fact that the stems of this variety tend to peel off in layers leaving various shades of bark on the stem. The most popular variety is called ‘Annabelle’.

Smooth hydrangeas are a lot like mopheads in terms of the shape and size of their flower heads, but the individual flowers are smaller, and because they always grow on new wood, they should be pruned after flowering.

Oak-leaved Hydrangea (Hydrangea quercifolia)

The beautiful oak-leaved hydrangea is native to the south-eastern U.S.A. where it grows as an under-storey shrub in mixed hardwood forests, often in the shade of large oaks, hickories, magnolias, American beech, etc.  It can often be found alongside streams and on forested hillsides, usually on calcareous soils, and often where limestone is at the ground surface.

Hydrangea Oak-leaf Image by Haerer from PixabayHydrangea Oak-leaf Image by Haerer from PixabayLong pendulous panicles of creamy-white flowers appear in mid to late summer and persist into autumn, morphing into delightful shades of pink as they age. By early winter the flowers are an attractive rusty-brown shade, and dry and papery. Both the fresh and dried flowers are excellent for the vase.

In the garden it is generally pruned and will grow about 2m tall and 1.5m wide, but under favourable conditions it can become quite a handsome looking shrub, reaching up to 2.5m tall, with an even wider spread. This stature, combined with the plants big, bright green and deeply lobed leaves make it stand out wherever it grows, and as summer draws to a close the summer foliage turns dramatic shades of rich, bronzy-red, purple, and coral, before dropping in winter, but in protected positions the lovely autumn leaves will persist. In winter when the branches are bare, the attractive cinnamon-orange bark that shreds and peels off in thin flakes from the larger stems can clearly be seen, together with the lovely young stems, covered in their soft, felt-like, light-brown bark.

The oak-leaved hydrangea thrives inland in the colder regions of South Africa which receive good summer rainfall, and is hardy to all but very severe frost. However, it is not suited to very hot and dry areas, and will flower best in the garden if it is watered moderately during prolonged dry spells.

It does best in a woodland situation, in partial to almost full shade, or full morning sun with afternoon shade.  This hydrangea cannot tolerate "wet feet" and can easily get root rot if it stands in soggy soil for even short periods. This is a tremendous advantage of this hydrangea, as it will tolerate much dryer locations than its cousins, thriving with very little attention.

Hydrangea arborescens Image by zoosnow from pixabayHydrangea arborescens Image by zoosnow from pixabayCultivation:

Hydrangeas can be planted in almost all of South Africa’s growing regions but do best in temperate regions which receive good summer rainfall. In geography, temperate latitudes of the Earth lie between the subtropics and the polar circles, like South Africa. Temperate means moderate, and although these regions have four distinct seasons: summer, autumn, winter and spring, the average yearly temperatures are not too extreme, being neither burning hot nor freezing cold.

Although some hydrangeas, like the oak-leaved hydrangea are known to be very hardy, generally all hydrangeas are hardy to frost, but the buds can be damaged by severe winter weather and freezing winds, so in very cold regions, site the plants in a sheltered part of the garden, mulch the roots well, and cover in winter, or plant them into pots which can be moved, or covered.

In hot and dry regions of South Africa hydrangeas will grow well only if they are provided with ample water, and shade, especially during the hottest time of the day.

Hydrangea macrophylla grows naturally in coastal regions and is perfectly happy in seaside gardens, but to look its best the plant will need some protection from strong winds; and in very hot and humid coastal and inland gardens, fungal diseases can be a problem, so ensure that the plants are correctly spaced to allow free air flow around the leaves, and water at ground level to keep the foliage dry.

The good news for Mediterranean-climate gardeners is that hydrangeas never die to the ground where winters are mild, so a bold summer floral display is guaranteed. The bad news is that hydrangeas grown in the winter rainfall regions will require generous irrigation in summer and perfect soil drainage.  

Although some species of hydrangea will grow in full sun if they are kept moist and the climate is not too hot, generally they are all shade lovers, and excessive midday heat will cause the plants to wilt. They do however require sunlight to flower well, performing best in dappled shade, or morning or late afternoon sun.  If you have a hydrangea that used to bloom well but now flowers only sparsely, evaluate whether the growth of nearby trees or shrubs have reduced the amount of light that reaches the plant. If so, you may want to consider moving the plant to a sunnier location, or pruning the offender to let in more sunlight.

Hydrangeas will adapt to most garden soils, but prefer a very fertile, loose, moisture retaining soil, which also drains well. They will adapt to well-prepared clay, clay loam, loam, loamy sand, sandy clay, sandy clay loam, and sandy loam soils

Image by Adriana Knop from PixabayImage by Adriana Knop from PixabayWhite hydrangea flowers are not affected by soil pH, although sometimes one will find that nature has added splashes of pink to the white flowers. And although some of the newer hydrangeas are bred to remain pink or blue, all the older Hydrangea macrophylla types are greatly affected by the pH of the soil. In strongly acid soil (pH below 6) hydrangea flowers turn blue. In alkaline soil (pH above 7) flowers turn pink or even red. In slightly acid or neutral soil (pH 6 to 7) blooms may be purple or a mixture of blue and pink on the same shrub, which is rather lovely.

Generally gardeners find it easier to work with nature, allowing their hydrangeas to naturally adapt and become either blue or pink, according to the pH of the soil, and then enhance the colour via feeding. This is much easier than attempting to force a blue hydrangea to flower pink, or vice-versa.

Hydrangeas growing in garden beds are hungry plants and do well when feed every six weeks or so from early spring until growth slows in autumn.  An initial high-nitrogen feed in early spring will encourage good leaf growth, but then you will then need to change to a more balanced feeder for flowering plants, to encourage good blooming.

Bear in mind that the type of fertiliser used can also affect flower colour, so choose commercial feeders which are specially developed for pink or blue hydrangeas. It may also be worth checking the pH of your tap water (you can use a pool test kit to do this). The pH of the water you will be using will also play a role in determining the colour of your hydrangeas.

Here are some simple methods adopted by gardeners to enhance the colours.

For pink blooms, dust the soil around the plants with agricultural or dolomitic lime every 2 to 4 weeks from spring onwards, watering it in well. Feed with a fertiliser with high phosphorus content like 2:3:2; where the middle number 3 in the N.P.K. fertiliser ratio is highest. Phosphorus helps to prevent the plant from taking up aluminium, thus enhancing the pink colours.

If you are aiming for a strong blue colour, avoid planting hydrangeas close to a concrete wall or foundation as concrete can leach lime into the soil, making it difficult to obtain a true blue colour. To enhance the colour of blue blooms work some aluminium sulphate into the soil around the roots in autumn, and apply 25g of aluminium sulphate dissolved in 5 litres of water at two-weekly intervals from early spring onwards. Mulch the roots in spring and autumn with acid compost or pine needles, and use a fertiliser that is low in phosphorus and high in potassium like 3:1:5 or 8:1:6; where the last number in the N.P.K. fertiliser ratio is highest, and the middle number or phosphorus, is low.

Because hydrangeas have very shallow root systems, plant them in holes that are wider than they are deep, around 60cm square and 45cm deep, adding generous quantities of compost. To counteract root competition under trees, grow hydrangeas in large containers and set these on bricks to prevent the tree’s thirsty roots finding their way up into your well-watered containers.

Because of their shallow roots, regular watering is also essential to keep them looking at their best, especially during dry or hot summer spells. Watering is reduced considerably during the dormant winter months, and mulching the soil helps to conserve water and increases humidity.

Hydrangeas grow well in pots. Image by Ben Kerckx from PixabayHydrangeas grow well in pots. Image by Ben Kerckx from PixabayGrowing Hydrangeas in Pots:

Potted mophead and lacecap forms of hydrangea are popular gifts during the festive season, but sadly, all too often they just seem to decline slowly indoors. To keep them looking at their best ensure that they are never allowed to wilt from lack of water. The potting soil in which they are planted is a very light mixture of peat and coir, which can dry out rapidly, so ensure that the soil remains evenly moist but not continually soggy either. If a plant does start to wilt, to rehydrate it immerse the whole container in water for a couple of hours. It is also important that the plant is placed indoors where the light is bright but where there is no direct sunlight. Feeding every two weeks will keep the plant looking its best. Once the flowers fade, plant into garden beds or larger pots, which can be placed in any shady part of the garden or patio.

If you want to transplant that little Christmas gift into a bigger pot, or perhaps you have a larger specimen from your garden centre, it is important to select the right size pot for your plant. Very small plants can be re-potted into larger pots every couple of years, so select a pot about two to three sizes bigger that the one the plant is currently in, and for larger garden specimens where the plants will be growing in the same pot for a long time, make sure that the pot is spacious and deep with a wide base, as the roots need plenty of space in order to thrive.

The type of hydrangea you choose will therefore determine the size of your pot. If you wish to move your pots around easily, select a light-weight one but one which is sturdy and enough so that the shrub doesn’t risk becoming top heavy and toppling over in the wind. A large terracotta container works well too, although it’s heavier to move, so you may wish to invest in a wheeled base. Plastic containers do not dry out as quickly as terracotta ones, and you could even use a wooden container with a wide base. The flowers of hydrangeas growing in concrete pots will turn pink.

Whichever container you choose, if it’s been used before, to avoid the spread of disease, make sure to clean and disinfect it thoroughly before planting. To prevent the drainage hole from becoming stopped up with roots or soil, line the bottom interior of the pot with a porous landscape fabric such as weed barrier. If you use gravel or other material in the bottom of the pot, lay the fabric over the gravel.

When growing hydrangeas in pots it is very important that the potting soil drains well to avoid waterlogging, while at the same time retaining sufficient moisture to ensure that the plant never dries out completely. Potted specimens will need more frequent watering than those growing in beds, so water regularly, never allowing the plants to wilt.

If you wish to specifically grow pink or blue hydrangeas, you could start out with a soil-less potting medium, and then feed with specific colour enhancing fertilisers on a regular basis. A coarse-textured soil-less potting medium can be made at home using bark, palm peat, or coir. Vermiculite, perlite and other inorganic materials like charcoal and washed river sand will further supply aeration and drainage.

For pink hydrangeas a good potting soil with a neutral pH can be added to the soil-less potting mixture, and for blue flowers add an acidic potting media with a low pH, such as those formulated for other acid-loving plants like azaleas and camellias can be added.

Regular feeding of potted plants with a specialist feeder for blue or pink hydrangeas is especially important to keep them looking stunning all season long.

Otherwise, potted hydrangeas are treated the same as those growing in garden beds.

Pruning:

No matter what type of hydrangea you are growing, until it reaches maturity it is not necessary to prune at all, but it is necessary to selectively prune out all the dead and very weak looking stems completely, cutting them out right down to ground level.

Should it become necessary to prune Oak-leaf hydrangeas, it is recommended that they are only pruned directly after flowering because they bloom on old wood and sets flower buds in late summer for next year. Therefore pruning at any other time of year won’t harm the plants but will result in even more of next year’s blossoms being lost.

Panicle varieties bloom solely on new wood, and can be cut back each year after blooming without concern.

Although mophead and lacecap hydrangeas do not require much pruning, traditionally South Africans prune them twice a year to keep them smaller– once very lightly after flowering and another harder pruning in June, July or August. This method is quite acceptable, but because Hydrangeas set new buds soon after blooming, many gardeners now prefer to do all their main pruning as soon as the flowers have faded in late summer.

Before jumping ahead and pruning your mopheads and lacecaps, first remove all the faded flower heads so you can sit back and get a better look at your plant. Notice that there are three distinct and different types of wood, according to their age.

The young slender stems reaching up from the base of the plant are from the current season’s growth, and at the end of these stems there is a large bud which will produce a short flowering shoot next summer, so do not prune these.

The older shoots will be two seasons old and would have flowered during the current season, so look for stems where you can see you have removed a dead flower. Look slightly further down the stem and you will find a cluster of large buds. Prune down to just above these buds.

If necessary bud bearing stems can be pruned back even further, up to 1/3 of the stem, but bear in mind that older types of hydrangeas flower on the older stems, and the mistake gardeners often make is to prune the older stems too hard and thus reducing their blooming potential. 

Older, thicker and heavier stems which have been producing for of two or more seasons will show signs of bearing several dead flower heads. Once these become unproductive and no longer bear well they can be pruned back right down to ground level. This will open up the bushes a bit to allow in more light, and therefore simulate new, vigorous growth the following season.

Propagation:

Propagation is easy from softwood tip cuttings taken in summer, or from cuttings of un-flowered shoots taken in early autumn. Layering is also simple; bend some of the younger branches to the ground and remove the leaves where the branch touches the ground. Cover the stem with soil and place a brick on top. Within one season the branch should have formed roots and can be cut away from the mother plant and transplanted.

Problems, Pests & Diseases:

It’s not uncommon for hydrangeas to produce lush foliage, but few or no flowers. This is often a result of over-feeding with a high nitrogen fertiliser, as nitrogen stimulates leaf growth at the expense of flowers. Another main cause of hydrangeas not blooming is incorrect pruning, or pruning at the wrong time.

A common reason for lack of flowering can be due to unfavourable weather conditions like early autumn freezes before the plant is totally dormant, or when warm temperatures in late winter and early spring break the plants dormancy,  but are immediately followed by early spring freezes. The severity of the damage caused by these freezes depends on how many of the buds have broken dormancy, and if a substantial portion of the buds on a stem were actively growing, the whole branch may die.

If the leaves of your hydrangeas start turning yellow but still have prominent green veins this is an iron deficiency called “chlorosis”. Rectify this by feeding your hydrangea with iron chelate at the recommended dosage, or foliar feed with micro-elements like Trelmix.

If your hydrangea leaves start turning a silvery-grey colour, this is a sure sign of red spider mite infestation, and if you look carefully underneath the leaves you will see minute red spiders and also possibly the fine webs they spin. Spray with any suitable insecticide like Biogrow ‘Bioneem’, following the instructions implicitly as this is the only way to fully break their breeding cycle. Adding a sticker to the spray will help it cling better to the surface of the leaves, and ensure that the entire plant especially the undersides of the leaves, are thoroughly covered with the spray. Red spiders thrive in sheltered or enclosed gardens, and can become a problem during hot and dry summer spells, so increase humidity by mulching the soil and frequently misting the plants down with water during these periods.

Also watch out for slugs which can be collected or baited, and aphids which can be blasted off with a jet of water, or controlled with Biogrow ‘Bioneem’.

Hydrangeas are prone to diseases like rust, powdery mildew, and leaf spot, and especially in humid regions. Copper based fungicides like Biogrow ‘Copper Soap’ can be used to prevent a broad spectrum of fungal infections. To help prevent these, correct spacing is essential to allow for free air flow around the leaves, and watering at ground level will help to keep the leaves dry.

Warning:

Hydrangeas are moderately toxic if eaten by humans, dogs, cats and horses, with all parts of the plant containing cyanogenic glycosides. Cyanide intoxication is rare and usually only produces more of a gastrointestinal disturbance. If ingested, stomach pain, nausea, vomiting, sweating, gastroenteritis, vomiting and diarrhoea, which may be bloody, can occur. If you suspect that a child or animal has ingested hydrangea it is advisable to consult your doctor or vet immediately.