Hydrangeas, the colour – It’s a Kind of Magic

Grown at Marwood Hill Gardens, North Devon

By Lin Collins

Here in Devon, Hydrangeas are affectionately known as ‘change-ables’. This is due to their seemingly magical ability of changing colour, often having different colours on the same plant, or even varying from one year to another. This is unusual plant behaviour and seems solely to occur in Hydrangeas – who can bring to mind any other flowering plant with this characteristic?

It is worth noting that it is the large- leaved Hydrangea (Hydrangea macrophylla) and its cultivars, either Mophead or Lacecap, which has this magical ability and is the predominant species grown at Marwood Hill Gardens.

The cause of the colour change is mostly due to the acidity (blue flowers) or alkalinity (pink/ red flowers) of the soil they are grown in. It is also apparent that the absorption of aluminium is essential for the production of blue flowers and this readily soluble in Acid soils pH4 to pH6.

It is not easy to make the soils more acidic to encourage permanent blue colouring, especially in mature plants well established in the ground.  More control can be obtained in tub or pot grown subjects, but why not just let your hydrangeas be what it wants to be – albeit changeable? Embrace the change!

At Marwood Hill Gardens we have an area dedicated to the large leaved hydrangea (Hydrangea macrophylla). This appears as a foaming mass of blue seemingly rolling down the North facing slope of the garden, known as the Hydrangea Walk. There are hydrangeas planted either side of the main path with smaller pathways meandering through this beautiful sea of blue. Due to the acidic nature of the soil here we have white, pale pink, deep pink, crimson, pale blue, deep blue and purple colours all represented.

Also, on the hillside we have some excellent plants of the Panicle Hydrangea (Hydrangea paniculata) and these make a spectacular show in the summer, although less colourful than the large leaved hydrangeas, they are none the less impressive.

Hydrangea macrophylla and its cultivars, either Mophead or Lacecap, lends itself to many different uses in the garden. For example:

• • • Grown on masse to create a large impact of colour

  
  

  • • Brighten up a semi-shaded area

  
  

  • • Adds interest on the margins of woodland

  
  

  • • As a singular specimen against a wall

  
  

  • • As the centrepiece on a lawn

  
  

  • • Tub or pot grown plants for rooms or conservatory’s

  
  

  • • Flower arranging and drying for winter decoration

  
  

  • Seaside gardens

Space will be the limiting factor in where to plant your hydrangea and which cultivar to choose.

The following is a list of favourites grown at Marwood Hill Gardens.

 https://shop.marwoodhillgarden.co.uk/s/search?q=hydrangea

Alpengluhen – Apline Glow

A lovely robust mophead with flowers that stay red in Acid soil but may go a lovely purple colour in soil with a pH below 6.5. Flowering usually from July to August on a 5ft shrub, an attractive addition in any garden.

Altona

An interesting Mophead with flowers that can be purplish plum to a smoky blue, changing to a vibrant brick red in Autumn.

Ayesha

A very distinct shrub from Japan. The mophead type flower head consists of lots of tint cupped flowers that resemble lilac. The colour can range from pale blue through white to pale pink and, unusual for hydrangeas, the flowers are slightly scented. Great to grown in pots or in a conservatory where the scent will be more noticeable.

Blaumeise – Blue Tit

An exceptional compact shrub, 3-4ft with beautiful lacecap flowerheads of an outstanding blue, continuing through to September when the sepals reverse and are dusky pink. Great grown in pots where acidity and feeding can be controlled to maintain the navy-blue colouring.

Blue Wave

A classic lacecap of the sturdy nature flowering from mid-August and often through to November. The sepals can be either blue or pink depending on pH. A large shrub best grown in partial shade as the flowers will lose colour and the foliage scorch in direct sunlight. A good cultivar for drying and general flower arrangement.

Frillibet

Another distinctive mophead. With serrated sepals tightly packed giving the flowerheads a frilly appearance. The sepals also reverse in autumn and go a lovely metallic like green. Flowering from mid-July to August on a 4-5ft shrub best grown in dappled shade.

Generale Vicomtesse de Vibraye

An abundantly flowering mophead with light blue or pink overcrowded sepals, ageing to sea green or dusky lilac. Can be used for drying. This large shrub can also be grown as a seaside plant in full sun.

Gentian Dome – Enziandom

On very acid soil this 4-5ft shrub can produce stunning deep blue flowers. The immature flowers start with white centres changing to pure blue and maturing to a plum colour. The flowering period can last well into mid-October. This mophead is ideal for cutting and drying.

Lanarth White

A lovely white lacecap with leaves of a very pale green. This shrub flowers abundantly on poor soil and prefers and open site. Ideal for seaside planting or a garden without shade. 4-5ft height with a long flowering period – July to September.

Libelle Dragon Fly

A vigorous white lacecap with large flowerheads. The sepals are cup shaped among the fertile blue flowers. A most attractive plant, best grown in some shade such as below trees where the

Madame Emile Mouillere

A very prolific white mophead which will grow in full sunlight and in tubs. In the garden it can make a large shrub up to 6ft and has a long flowering period from July through to October.

Merveille Sanguine 

A magnificent slow growing plant with wonderful dark flowers and foliage. A mophead that stays red or goes and even darker red on very acidic soils. Well worth growing as a pot plant or in any garden with limited space.

Mousseline 

Another outstanding mophead of strong stature which will layer itself to make a large shrub. It makes a wonderful display of flowers that densely cover the whole shrub until late in the season, often only stopped by the first frosts in November. The flowerheads are large with young sepals opening a creamy white changing to a pale blue, or rosy pink, on maturity. A worthwhile shrub to make a bold statement in a large garden. Always best when regularly dead headed and properly pruned.

Mowe – Seagill

A good colourful shrub 4-5ft high with lacecap flowerheads produced from July to September. On very acid soils the outer sepals (infertile flowers) can be an eye-catching purple with central small fertile flowers of blue. Alternatively on alkaline soils the sepals are red with pink fertile flowers. Great planted on its own or amongst other small shrubs.

Parsifal

A mophead with lovely, rounded inflorescences and although relatively small, they are produced over a long period – June to October. The sepals overlap each other and are serrated giving an overall smoothed round appearance. The colour is usually in the red/ purple range but can be deep blue on acid soils, often having flowerheads with both colours represented – a changeable indeed.

Rotschwanz Redstart 

A very beautiful mophead of small stature but tremendous impact when in flower (July- August). The sepals, usually four, are grooved and twisted, and surround a multitude of small central fertile flowers. The colour stays in the red range, going a deep crimson on acid soil.

Veitchii

A rather straggly shrub which can get quote large, easily up to 6ft high and wide but responds will to correct pruning. It is a summer flowering lacecap with 3 or 4 rather large white sepals which reverse in Autumn and are a lovely pale lilac. The small central fertile flowers are pink in bud but open a mid-blue. Another good subject for flower arrangers. Suitable for large gardens.

PRUNING of the large leaved hydrangea (macrophylla)

Hydrangeas do not have to be pruned; they will grow and flower perfectly well without. However, no pruning is always better than the wrong pruning or indiscriminate hacking. Correct pruning will help the plant in many ways. By removing dead, diseased, weather damaged and excessive growth, the production of flowers and overall vigour of the plant will be greatly increased – after all we grown hydrangeas for their flamboyant and colourful flower display.

The most regular and often essential form of pruning in annual dead heading. This is the removal of the past season old and dead flower heads. These are removed to just above the top pair of buds on the stem – these will be this season’s flower. The removal of these dead heads greatly improves the appearance of the whole plant – on the lacecaps it also prevents the production of seed which is often unnecessary.

Here at Marwood Hill Gardens we start this process in the winter as we have a great number of shrubs to deal with, but in a garden with only a small number, it is best done in the spring after the last frosts have gibe, but before the young green buds have burst into growth.

The next form of pruning is to maintain a good shape and vigorous flowering stems. On more mature plants this is achieved by removing about a third of the oldest growth at ground level to allow in more light and aid into the centre of the plant. This will encourage new growth from the base but remember that these new stems will not produce flowers until the next season.

Hydrangeas often spread by layering; this is where the stem grows down to the ground, roots itself and sets off again as a new plant. This new growth can be completely removed by cutting back to an upward growing shoot on the parent plant. This will curtail the outward spread and keep the overall plant contained. These rooted layers can always be grown on elsewhere, in pots or given to both friends and enemies. This is carried out in February/ March.

If necessary, a very drastic form of pruning can be carried out by cutting back all of the stems to ground level. This usually occurs where plants have become overgrown and possibly neglected. Regrowth from these plants will need to be thinned out as good strong flowering stems will take a few years to re-establish. This must be done well after the risks of frost has passed otherwise the new young shoots will be damaged and may not recover at all.

We have had to do this extreme pruning to a group of hydrangeas at Marwood, that had been completely overwhelmed by that ubiquitous foe – the bramble! All hope now rests on our magical hydrangeas to overcome and return to their former splendour! Phew!