Hydrangeas have always been a favourite of mine. Their charming old-fashioned flowers are a stalwart of the cottage garden. I love their variegated flowers and their unusual and exquisite colour combinations, which are constantly changing as the flowers age.They are usually planted in groups or in shrub borders and are highly ornamental. Our hydrangeas are massed in their very own bed (photo 1), but they can be planted in a shrub border along a path (photo 2) .Moreover, they are tough plants, often surviving long after their original garden or house has vanished. In my childhood, we had masses of them down by the creek, way beyond the garden boundary. When we built our cottage at Dorrigo on the site of the old ruins, the hydrangea bushes were enormous- at least 3 metres tall- and even though we pruned them right back, within two seasons, they were back up at the level of the verandah roof again! Here is an old photo of one of the original shrubs on the old house site during the building phase.Hydrangeas belong to the Family Hydrangeacae . Their genus name is Hydrangea and contains up to 100 deciduous and evergreen shrubs, small trees and climbers. They are mostly found in temperate Asia (China, Japan, Korea and Himalayas) with a few species from North and South America. Their natural habitat is moist woodlands. They were introduced into Europe in 1735. Their name is derived from 2 Greek words : ‘Hydor’ meaning ‘water’ and ‘angeion’ meaning ‘vessel’, referring to the cup-shaped seedpods. They are thought to be over 140 million years old.Most hydrangeas are 1-3 metre tall shrubs with brittle pithy stems and dark green oval leaves with serrated edges. They are grown for their beautiful flower heads of white, red, pink, purple and blue. Small fertile flowers are surrounded by larger eye-catching 4-petalled sterile petals or bracts. You should be able to see some of the fertile florets in the following photos:The most popular species is Hydrangea macrophylla or Bigleaf Hydrangea. It is native to Japan and has thick individual canes, which grow from the base of the plant, big flat oval toothed leaves 4-6 inches long and 3-5 inches wide and huge round flowerheads up to 8 inches in diameter.There are 2 types of H. macrophylla :
• Mopheads (Hortensias): snowball type blooms; over 600 named cultivars, including more compact and dwarf varieties. We have the standard H. macrophylla, as can be seen in the photos above. There is also a variety called Ayesha, which is 1.5-2 metres tall and is photographed below:• Lace Caps: showy open sterile flowers hang down from a flat centre of tiny fertile buds; 20 cultivars.Hydrangeas flower in Australia from late January to February and into Autumn on second year growth. Their flower pigment changes colour in the presence of Aluminium ions, which is translated into soil pH, so :
- Soils with a relatively high availability of aluminium ions : acidic : pH 1-6 produce blue flowers and
- Soils with low levels of aluminium ions : alkaline soils : pH 8-12 produce pink or red flowers.
- When the pH is about 6, mauve flowers are produced.
Having said that, we did try checking the pH of our hydrangea bed. It was 6.5 under the white hydrangea and 7.6 under the pink hydrangea, but the soil under the blue and mauve hydrangeas was also 7.6! So either our pH measurer is dodgy, the roots of the blue hydrangea are in pockets of acid soil, which we cannot reach to test, or maybe the relative availability of aluminium ions is more important than pH as a colour determining factor. All a bit of a mystery, but it’s great having the colour variability!
The colour of hydrangea flowers can be manipulated by adding substances to the soil to change the pH, but it can take up to 2-3 years to achieve the final colour. Note : White flowers are not affected by pH or aluminium levels eg AnnabelleTo change pink flowers to blue : Add a blueing tonic containing aluminium and iron (eg 1 tbsp powdered alum or aluminium sulphate) to 1 gallon water. Apply once per month in March and April and again in August, September and October. Coffee grounds, organic matter and grass clippings, as well as a fertilizer low in phosphorous and high in potassium, can also predispose to blue blooms. In the past, iron nails and tin were often added to the soil . With our blacksmithing past, it’s no wonder that we have so many blue flowers!!! It is best not to decrease the pH below 5.0, otherwise the leaves will yellow.To change blue blooms to pink : Add 1 cup Hydrangea Pinking or dolomite lime (calcium carbonate) in 1 gallon water to the soil in Spring and a fertilizer with high levels of phosphorous.Hydrangeas are very adaptable plants , but their ideal growing requirements are:
• Moist rich composted soil with good drainage. They don’t like heavy clay soils.
• Partial or dappled shade for most of the day or at least past 11am. An easterly to southerly aspect is best in the Southern Hemisphere. Our hydrangea bed is in an ideal location on the south-east corner of the house (see photo below). Ultraviolet exposure burns hydrangea flowers and leaves. Full sun and wind dry the plants out. Avoid heavy shade (insufficient light) or positions under trees due to root competition.
• Regular watering, especially in late Spring to Summer: a deep soaking at least 1-2 times a week
• Mulch: apply bark chips, leaves, pine needles or straw in Autumn, as the fibrous root system is close to the soil surface
• Low fertilizer needs, though use a slow release fertilizer with micronutrients in Spring if the soil is sandy and light.Pests are minimal, though slugs like hydrangeas, but there are a few diseases including : powdery mildew, gray mould, rust, ring spot virus, leaf spots and white hydrangea scale. Powdery mildew occurs in warm wet weather or when there is too much shade or not enough water. The leaves are covered with a light grey powder, which starts on the bottom leaves and works its way up and it is worse on mophead varieties. It can be prevented by spraying the plants with 2 cups of milk in a bucket of water. White hydrangea scale can be picked off or if it is bad, sprayed with Eco-oil. Macrophyllas can also suffer from iron chlorosis (see photo below), especially in soil with a high pH, where less iron is available, so use a chelated iron fertilizer. For more on iron chlorosis, see : https://www.ppdl.purdue.edu/PPDL/weeklypics/5-10-10.html Hydrangeas should be pruned every year to avoid the plants becoming leggy with dead branches and less flowering. Pruning should be done in late Winter (July/ August), when the plants are dormant. Each stem has a maximum life of 5-6 years. Old dead wood should be removed – look for exfoliating stems- and prune right back to the ground. Otherwise, trim back the green growth of the current season to ¼ inch above the 2 plump eyes or leaf buds closest to the ground. Do not prune stems, which haven’t flowered yet, as they will flower the following season. Apply compost after pruning. The photos below show our drastic initial prune at Dorrigo and the growth within one season.Hydrangeas can be propagated by softwood cuttings taken in Summer, hardwood cuttings taken in Winter and seed. If you need to transplant a plant, move it when dormant in Winter.Other species of Hydrangeas :
• H. paniculata : The Panicle or Cluster-flowering Hydrangea : Has vertical growth and long plumes of creamy-white flowers, turning a very light pink; Similar to lacecaps in late Summer; Deciduous; Very cold hardy and tolerates more sun, dry spells and frost than other species; Prefers semi-shade; Prune in late Spring for more flowers.
• H. quercifolia : Oak-leafed Hydrangea : Native to North America; Similar shaped leaves to Acer macrophyllum, which turn a deep mahogany red in Autumn; Long cone-shaped panicles of white to light pink plumes, which last on the bush until Winter; Can tolerate sunnier conditions and drier soils than other species, but does not like soggy soil! If it is affected by root rot, the bush looks wilted, but not for want of water, and it is usually too late by this stage, so good drainage is essential; Prune early Spring.
• H. petiolaris: A climbing hydrangea : Native to Japan, Korea and Sakhalin, Eastern Siberia; Very slow growth; Can reach 9-15m high and 2m wide and takes 10 years to bloom; White lace cap type bloom in early to mid Summer; Likes filtered light; Do not plant against the wall of your house, as it leaves a residue, which is very difficult to remove.
• H. anomala : Another climbing hydrangea, but native to China, Myanmar and Himalayas; Grows up to 12m up trees and rock faces; Needs a support to climb or will form a ground cover 1.5m high; Popular with nesting birds, especially blackbirds. 15cm diameter flower corymbs in Summer; Does not require pruning.
• H. arborescens : Wild Hydrangea/ Smooth Hydrangea/ Sevenbark : Cultivars : ‘Grandiflora’; ‘Annabelle’ : Native to Eastern United States of America; 3-5 feet high; Thin leaves, so avoid bright sunlight; Large creamy-white dome-shaped flowers up to 1 foot diameter from Summer to Autumn; Cut back vigorously to 20cm at the end of Spring.
• H. serrata : Mountain Hydrangea/ Tea of Heaven : Native to the mountains of Japan and Korea; Similar to H. macrophylla but hardier, smaller and more compact with smaller leaves and flowers; Panicles of blue and pink flowers in Summer and Autumn with showy sterile and less showy fertile florets in each cluster; Deciduous.Hydrangeas are beautiful in a vase and last a long time, so long as the water is regularly changed and preservative added. Cutting their stems stops the colour-changing process and the further along the colour-change of the flower has progressed, the longer their vase life. A fully grown head near the end of its colour change can last up to 2-3 weeks. These photos show the development of colour as the blooms mature.Recut stems on the diagonal and do not split, sear or bash. Strip any leaves which would be under water. Preservative is essential. I love the subtle shades and colour combinations in the hydrangea petals, as well as the elegance of pure white blooms.They can also be dried. For drying, cut flowers late in the season, when they are almost dry, and cut them at night time when the humidity is low. Put in 3cm of water only and do not add extra water. Alternatively, hang stems upside down in a warm, dry, dark, airy room for 2-3 weeks. Keep them out of sunlight to prevent fading. These autumnal mottly colours are seen late in the season:
In the language of flowers, hydrangeas mean : ‘grace, beauty and abundance’, as well as ‘gratefulness and sincere feelings’. Pink hydrangeas are increasingly popular in Asia, where they mean ‘You are the beat of my heart’. My daughter Caroline used watercolours in this beautiful painting of a vase of hydrangeas.
In Japan, a sweet tea, ama-cha甘茶 , or’ Tea of Heaven’ , is made out of the dried leaves of H. serrata. The sweet substance in the leaves is phyllodulcin. The leaves are crumpled, steamed and dried to produce dark brown tea leaves, which are then used in kan-butsu-e (the Buddha bathing ceremony) on 8 April, supposedly Buddha’s birthday, in Japan. The tea is poured over a statue of Buddha and served to people in attendance. In Korea, H. serrata (hangul 산수국; Hanja 山水菊 ) is used to make a herbal tea called sugukcha 수국차 or ilsulcha이슬차. Hydrangea roots and rhizomes are diuretic and are sometimes used to treat urinary tract problems. However, great care must be taken as all parts of the plant contain cyanogenic glycosides and can be moderately toxic if eaten. H. paniculata is sometimes smoked as an intoxicant, even though it can cause illness and death from cyanide poisoning.