Hydrangea

With their large, colourful flowerheads, hydrangeas can put on a fine late-season show, writes Sarah Morgan.

Hydrangea quercifolia AGM - photo: Adrian Thomas
Hydrangea quercifolia AGM - photo: Adrian Thomas

Landscape designers love the huge cream and lime-green flowers of Hydrangea arborescens 'Annabelle' Award of Garden Merit (AGM) and H. paniculata 'Limelight', two of today's bestsellers.

First introduced around 300 years ago, this genus' showy flowers have always attracted landscapers and florists. Today there are hundreds to choose from in blue, pink, lilac, white, cream or lime-green. There are also a few yellow-flowered types like H. scandens.

Each flowerhead consists of two different kinds of flowers - tiny and fertile true flowers, which have nectar, and larger sterile flowers, technically called sepals, which are the more eye-catching. Also known as hortensias, some varieties with their unique flower shapes are loosely called lacecaps, mopheads or panicles. They flower from June, reaching a climax in autumn when many show their strongest colour.

Over 80 species of deciduous or evergreen shrubs or climbers exist, widely distributed, often in woodlands across East Asia and North and South America. However, we grow many cultivars from just a few species. They are mostly deciduous shrubs - with exceptions like H. aspera Villosa Group, which forms a beautiful small tree, or the slow-growing climber H. anomala subsp. petiolaris AGM, a shade lover.

Hydrangeas enjoy moderately rich and dampish soils and grow in sun or partial shade. Many are naturally woodland plants so a west- or north-west-facing wall is ideal for shade, warmth and shelter.

They are easy to grow as long as they are protected from cold winds and frost. They can become chlorotic or yellow-leaved due to thin or limey soils, though this can be treated with doses of sequestered iron. Where the soil is not acid, H. macrophylla and H. serrata cultivars famously lose their blue flower colour. Colourants can reverse this but a lot of repeat doses are needed and it is not really worth the effort.

Pruning depends on the species. H. paniculata and H. arborescens flower on the current season's growth and are cut back hard in spring. This makes for bigger flowers, while lighter pruning produces smaller ones. Both are recommended for frost-prone gardens as they come into growth late. H. macrophylla and H. serrata are lightly pruned in spring and old brown flowers are cut back to the nearest bud behind.

Plants suffer from a wide range of pests like aphids, scale or vine weevils, but can weather most attacks if kept healthy. Their leaves also get fungus blotches and they are susceptible to honey fungus.

Stock is increased by softwood, semi-ripe or hardwood cuttings. Layering is possible and some sucker of their own accord. Seed is used, although unless from the species, they may not come true.

WHAT THE SPECIALISTS SAY

- Nick Macer, owner, Pan-Global Plants, Gloucestershire

"Generally, hydrangeas love acid soils but don't need it to grow well. A lot of people think that H. serrata and H. macrophylla will only grow on acid soil because their flowers grow blue when they do, but I grow them on very limey soil here and they grow well.

"H. serrata 'Kiyosumi' is a fabulous new cultivar with new leaf growth flushed with burgundy and a sheen to the leaf. The flowers are dainty lacecaps in a mix of white and red. H. serrata is best grown in semi-shade as they are natural woodland-edge plants found at high altitudes.

"Opposite are the H. macrophylla types, which are a seaside plant excellent for coastal planting. H. serrata generally has slimmer, daintier leaves and lacecap flowers and smaller heads.

"H. aspera is usually larger-growing with hairier leaves and bigger foliage. It loves semi-shade but will grow in sun too. H. aspera 'Macrophylla' Award of Garden Merit (AGM) has a wonderful combination of blue lacecaps with white insides."

Rachel Kendall, Hydrangea growing assistant, Ashwood Nurseries, West Midlands "We grow a lot of the traditional mophead and lacecap varieties, which have been around for years as they are such good plants.

"One of my favourites is H. paniculata 'Phantom' because it produces massive, creamy white flowers that go pink in autumn. It flowers on the same year's wood so is chopped back hard in February.

"A good one is H. serrata 'Grayswood' AGM, which is a tall, white lacecap that looks great in a shady woodland setting, where it reflects the light. The blue lacecap H. serrata 'Blue Deckle' is compact and tolerates a more exposed site.

"We like stocking the more compact forms of H. macrophylla with good, strong stems that don't need any support and hold their own blooms up. Some of the large mophead varieties make such massive flowers that they pull the branches down, then all the flowers flop over each other."

IN PRACTICE

- Rebecca Wells, garden designer, Devon

"The climber H. anomala subsp. petiolaris AGM is valuable on a north-facing wall because it has so many seasons of interest. The faded flowerheads are visible throughout the winter and it comes into leaf fairly quickly in spring, while in autumn the foliage turns a fantastic butter-yellow, which brings a bit of sunshine into an otherwise dark place. The only drawback is that it tends to sulk for a couple of years before it gets going. I like H. paniculata 'Grandiflora' AGM, particularly when it has its lower branches pruned so it looks like a small tree, allowing early spring planting underneath."

SPECIES AND CULTIVARS

- H. anomala subsp. petiolaris Award of Garden Merit (AGM) is a deciduous climber reaching up to 16m tall and grows in shade. In early summer it has corymbs of creamy white flowers 25cm across.

- H. arborescens 'Annabelle' AGM has 20cm panicles of flowers, first lime-green then creamy white from midsummer to early autumn. It is a 1.5m rounded shrub that needs staking.

- H. arborescens 'Grandiflora' AGM carries lime-green flowers turning to white with smaller flowerheads than 'Annabelle' but larger ray florets.

- H. aspera 'Macrophylla' AGM is a lacecap with blue to mauve flowers and white ray florets. It grows to 1.4m tall by 2m wide and needs protection from wind and frost.

- H. aspera Villosa Group AGM features blue to violet fertile flowers and pale pink to blue ray florets. It grows to 4m tall and 4.5m wide and can form a deciduous shrub or small tree.

- H. aspera subsp. sargentiana AGM displays flattened corymbs of blue to purple flowers surrounded by white, sterile flowers and grows to 3m or more.

- H. macrophylla 'Ami Pasquier' AGM is a mophead with deep red, smallish flowers, which change to wine-purple on acid soils. It grows to 1.5m with a 2m spread.

- H. macrophylla 'Europa' AGM has pink to lilac mophead flowers with cream centres and flowers from June to autumn.

- H. macrophylla 'Generale Vicomtesse de Vibraye' AGM is a mophead with light-blue flowers on acid soil, turning pink in alkaline soil. It grows to approximately 2m tall.

- H. macrophylla 'Lanarth White' AGM is a lacecap, featuring big white ray florets and blue to lilac fertile flowers, suitable for seaside planting as it tolerates poor soils and full sun. It grows to 1.5m.

- H. macrophylla 'Madame Emile Mouillere' AGM is a mophead with large, white flowers, pink-tinged with a pink to blue eye. It flowers from July and grows to 1.8m tall.

- H. macrophylla 'Mariesii Grandiflora' AGM is a very floriferous lacecap with white to lilac-blue flowers and grows to approximately 1.5m.

- H. macrophylla 'Nigra' AGM is a late-season mophead with pink, purple or blue flowers. The leaves turn bronze in autumn.

- H. macrophylla 'Rotschwanz' forms a compact bush with large lacecap flowers in blue, red or lilac.

- H. paniculata 'Grandiflora' AGM carries decorative panicles of large white flowerheads maturing with a pink flush from July to September.

- H. paniculata 'Greenspire' features white flowerheads, which fade to green. It is one of the most popular recent introductions and flowers reliably even when young.

- H. paniculata 'Kyushu' AGM displays white flower panicles and unusually dark, glossy leaves.

- H. paniculata 'Limelight' carries large white flowerheads that age to a pinkish colour in late summer.

- H. quercifolia AGM, the oak-leaved species, has dark green, oak-like leaves, which turn coppery red in autumn. Its flowers are white.

- H. serrata 'Bluebird' AGM features blue or pink lacecap flowers, depending on soil acidity, borne over a long period. The leaves have good autumn colour. It grows to 180cm in 10 years and requires a sheltered site.

- H. serrata 'Blue Deckle' is a smaller cultivar with pink or blue flowers with serrated sepals on the ray florets and autumn leaf colour. It flowers from July through to September.

- H. serrata 'Kiyosumi' displays red-tinted new growth and pink-flushed, white lacecap flowers. It is a rare Japanese form and grows to 1m tall.

- H. serrata 'Grayswood' AGM is a tall white lacecap, which gradually changes to dark pink. It flowers from August onwards.


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