Guest Blog: Dr David Roger Lloyd – Revisiting Hydrangeas

Once the staple of the suburban front garden, Hydrangeas fell out of favour in the nineties, even being considered vulgar and in bad taste. Well, all that has changed and Hydrangeas are back in the mainstream and with gusto. There are now up to 12 species in general cultivation, with many more varieties in a wide range of colours, thanks to active breeding programmes. We now have Hydrangeas for almost every garden situation and they peak at that difficult time from late summer into autumn.

Hydrangeas are ideal for our climate in UK. Most are fully hardy and, although they can be affected by late frosts, they will recover. They will grow in any soil, although soil acidity will play its part in flower colour. They are ideally suited for dappled shade but some will happily grow in full shade (Hydrangea aspera) whilst others thrive in full sun (Hydrangea paniculata). Their size can range from 1 foot to 12 feet, and higher for climbing species.

The flower heads come in three shapes, mophead, lacecap and conical with a colour range from white, green, pink, red, lavender, blue, purple to wine dark. You can grow them as shrubs, climbers, scramblers, container plants, standards and house plants and they make wonderful fresh cut and dried flowers. What more could you possibly ask for?

Flower Form and Colour

The colour of Hydrangea flowers has always been an active point of discussion. It varies with season, soil and fertilisers. White flowers often start as pale green and will then blush to pink and red as they age. Blue flowers can also start as pale green. This adds an exciting dynamic to the growing season and in autumn, Hydrangeas can display a range of subtle hues on one plant. This shows flowers on the same plant on the same day.

However, Hydrangea macrophylla, particularly the classic mopheads, can sometimes be pink and sometimes blue. Blue colour can only be achieved in acid soil because a lower pH is required for the uptake of aluminium from the soil. The blue colour is an aluminium complex and blue flowers contain ten times more aluminium than pink flowers from the same plant grown in a different soil. Even cuttings from a blue Hydrangea will be pink, if rooted in general purpose compost because of its pH.

If your soil is not acidic but you want beautiful blue Hydrangeas, grow them in pots. Use an ericaceous compost and water in a Hydrangea colourant, which are widely available. These products contain soluble forms of aluminium sulphate. So, you could also simply buy some straight aluminium sulphate, dissolving it in water at 3g per litre, and water you plant with it. Avoid using certain fertilizers with Hydrangeas – eg fish, blood and bone meal, because these can bind up the aluminium and prevent absorption.

Right: Hydrangea macrophylla ‘Ayesha’

Cut Flowers

Hydrangeas also provide wonderful cut flowers, with white ones widely used in bridal bouquets and wedding displays. However, cutting Hydrangea flowers does require a little care. Choose blooms that are fully out and collect the flowers in the morning when they are fully hydrated. It would even be a good idea to water the plant the night before. They will wilt quickly, so cut the stem on a diagonal, remove some of the lower leaves and place immediately into water because the cut end will seal quickly.

To ensure even greater success, you can immerse and store the whole flower head in water. Then, before putting it into a vase, make a one inch cut up the stem and plunge momentarily into water that has just been boiled. This will prolong the vase life. If your flowers have wilted beforehand, follow the same procedure – immerse in water for a few hours, split the stem, dunk in boiling water and they will recover. Then you can leave them and they will eventually dry with elegance and can be kept all winter.

Left: Hydrangea aspera ‘Kawakamii’

Care and Maintenance

Hydrangeas look at their best in an informal woodland setting or as the understorey beneath deciduous trees. They also associate well with Rhododendrons, Camellias and Magnolias which enjoy the same soil conditions and can provide some wind protection. Be careful, though, to allow the Hydrangeas their space so as to avoid any root competition. Hydrangeas do not want to be dry. They need moisture, but neither do they like being waterlogged. They have great impact in herbaceous borders because they perform from June to first frost and other plants help with some shade protection. Avoid frost pockets and ideally plant where they are shaded from the mid-day sun. Don’t forget to mulch in the Spring and feed – we use Maxicrop or a tomato feed during flowering. They are greedy plants and will respond and deliver.

However, whilst these are good generalisations, if you want the beauty and impact of Hydrangeas in a sunnier position or in containers on your patio or terrace, you’ll find that Hydrangea paniculata and Hydrangea arborescens will perform well for you. These species are also good when planted as hedges. They are robust to pruning and Hydrangea arborescens benefits from the mutual support of group planting.

Right: Hydrangea macrophylla ‘Rotschwanz’

Pruning

We prune in early March. The faded flowerheads still look good through the winter and provide a little frost protection for the buds below. Most Hydrangeas flower on last year’s growth so only need dead heading down to the first bud. Cutting these back any deeper risks the loss of this season’s flowers. Of course, it may be necessary to reshape or rationalise the appearance of the plant, but do this judiciously and leave enough flowering buds for this season.

Two species however, Hydrangea arborescens and Hydrangea paniculata, flower on this season’s growth and so pruning can be more radical to maintain the size, shape and vigour of the plants. For example, some growers cut the popular Hydrangea arborescens ‘Annabelle’ down to the ground. Hard pruning means that flowers tend to be fewer, larger and later. So more gentle pruning will result in more flowers, smaller and earlier. We tend to prune back to two viable nodes/buds which keeps the plants compact and floriferous.

Left: Hydrangea aspera ‘Hot Chocolate’

Selection

We are now really spoiled for choice with the range of Hydrangeas commercially available. The following is a selection from across the species and from our garden at Highfield Farm.

Hydrangea macrophylla

There is a bewildering and growing number of varieties available in both mophead and lacecap forms. These are the ones that show colour variability. Some favourites are:

• Hydrangea macrophylla ‘Lanarth White’ – pure white lacecap to brighten up a shady spot (Right)
• Hydrangea macrophylla ‘Rotschwanz’ a red lacecap for all soils
• Hydrangea macrophylla ‘Ayesha’ with lightly scented, cupped florets – pH sensitive colour 
• Hydrangea macrophylla ‘Merveille Sanguine’ with burgundy leaves and wine red/purple flowers

Hydrangea arborescens

North American species from the Appalachian Mountains. ‘Annabelle’, with its large white mophead flowers has become very popular. Its is also available in pink form. Both are prone to drooping, particularly after rain. Look out for a new variety, ‘Strong Annabelle’, which is more robust. Our favourite is ‘Heyes Starbust’, with its myriad of little double star-like flowers which start green and turn to white. Best grown in light shade.

Hydrangea paniculata (Left: Terrace at Highfields with Hydrangea paniculata ‘Early Sensation’ and Limelight’)

We are again spoiled for choice with this species with varieties like ‘Limelight’, ‘Vanille Fraise’ and ‘Phantom’ proving very popular. Flowers form large cones or panicles with colours from green to white to pink to red. Ideal for containers and as standards. We grow ‘Limelight’ and ‘Levana’ as standards and have ‘Early Sensation’ and ‘Confetti’ in containers. A favourite at Highfields is ‘Le Vasterival’ or ‘Great Star’ with its huge propeller-like florets.

Hydrangea serrata

This is quite a delicate species, mainly from the mountains of Japan and usually lacecaps. The flower colour is pH sensitive. Some of our favourites are ‘Kyosumi’, with its delicate pink margins on white florets and ‘Kurenai’ with its dark leaves and deep pink flowers. However, for biggest impact choose ‘ Preziosa’, a mophead with flowers that start white, turn to bubblegum pink then fade to red.

Hydrangea quercifolia

Another American woodland species which has its characteristic oak-shaped leaves which will turn a beautiful wine red in the autumn. It bears large panicles of single or double white flowers which will turn red late in the season. Two favourites of ours are ‘Snow Queen’ with single flowers and ‘Snowflake’ with doubles.

Hydrangea aspera

This species can have enormous, hairy leaves and sports large, mainly, white lacecap flowers, often with vivid blue stamens on the fertile florets. They grow happily in shaded locations. Popular varieties are ‘Villosa’, ‘Sargentiana’ and ‘Mauvette’. A favourite here is ‘Kawakamii’ but the showstopper at Highfields is ‘Hot Chocolate’ with its dark leaves with wine-red reverses, vivid pink flowers with electric blue stamens.

Climbing Hydrangeas

Everyone is probably familiar with Hydrangea petiolaris, a vigorous, self-clinging lacecap Hydrangea which famously grows on north facing walls. However, may I suggest two others. Hydrangea seemanii from Mexico has the advantage of evergreen, shiny leaves, is self-clinging and has lovely open white lacecaps and Hydrangea hydrangeoides ‘Moonlight’, which used to be called Schizophragma which has a beautifully delicate flower form and grows happily as a scrambler over walls, fences or through other plants.

Garland Hydrangeas

A recent introduction and the first ‘intersectional’ or cross-species Hydrangea. This is a compact form, ideally suited for container growing, and has the real merit of flowering along the stem not just at the tip like all other Hydrangeas. The variety ‘Runaway Bride’ was Chelsea ‘Plant of the Year’ in 2018. It also has lovely autumn colour.

Right: Hydrangea Walk at Highfields Farm Garden

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Left: Hydrangea arborescent ‘Annabelle’ and ‘Pink Annabelle’