How to make the most of hydrangeas to guarantee a display of colour

How to make the most of hydrangeas to guarantee a display of colour
Hydrangeas are likely to be grateful for the damp spring and summer we experienced this year. Picture: iStock

Peter Dowdall has advice on making the most of a bloom that guarantees a display of colour.

IT WOULDN’T be August without hydrangeas and what a display they are giving this year. I think they must be grateful for the damp spring and summer we experienced so far this year or perhaps they are thanking the climate for the prolonged spell of high temperatures and sunshine we experienced during 2018. Whatever the reason, hydrangeas this year are looking better than ever.

When we think of this genus we think, often exclusively of the “mophead” or “lacecap” types, both of which are of the species Hydrangea macrophylla. These are pH-sensitive plants, which quite simply means that the flower colour will be dependent on the pH of the soil. Now, if you are not concerned which colour blooms are produced then that needn’t concern you one iota as they will thrive in most soils, ideally preferring soils which are rich in organic matter and humus content, moisture-retentive and in semi-shade.

However, if it is all about the correct colour hue for your garden then things can change. Quite simply, acid soil will mean your Hydrangea will produce blue flowers and limey soil will give you pink blooms. Add Aluminium Sulfate to limey soil to promote more blue colour and add lime to acid soils to turn them pink. If you’re not sure what the pH of your soil is you can get simple pH testers in most garden centres or alternatively, wait for your hydrangea to flower and that will tell you the pH more accurately than any tester.

Aluminium sulfate, which will be found in the garden centre as “hydrangea colourant” can be applied easily by dissolving 100g in 10l of water and then drenching the soil around your plants with the solution. Don’t apply the solution to the foliage or stems of the plant as this could burn it. Do this about once a week or every ten days during the growing season and even if you have limey or alkaline soil you will still be able to enjoy pure blue hydrangeas. In fact, it will intensify the tone of any blue hydrangea, even if your soil is acidic.

To change them the other way, to turn blue Hydrangeas pink, apply a handful, about 10g of granular garden lime around the base of each plant. This should only need to be done about once a year, in the springtime.

Over the last few years, whilst I still adore the range of colours, the vibrancy and sheer luxury provided by the macrophylla types, I am becoming obsessed with the whites and different species, namely the H. arborescens ‘Annabelle’ and the paniculatas of which there are many and the range available is increasing each year.

‘Annabelle’ produces masses of flouncy, oversized blooms of the purest white that you can imagine. I say they are oversized because often the stems fall beneath the size and weight of the blooms and for this reason I would advise staking them with some of those metal arched or linked stakes which act to support the stems as opposed to the traditional bamboos which need to be tied to each individual stem.

There is also a pink form of ‘Annabelle’ but for my money, it’s not worth it, I’m not as keen on it as I am the pure white form.

Hydrangea paniculata or the panicled Hydrangea is a species native to China and Japan and left to its own devices will become quite large. Some varieties will grow higher than two or even three metres. However, I would advise pruning in early spring, not just to keep the plant in check and stop it from becoming too unruly but also to promote larger flowers.

The paniculate hydrangeas produce blooms of pure white which are conical in shape and a specimen in full bloom will literally stop you in your tracks. As the flowers age and as summer becomes autumn, so too do the flowers, taking on a beautiful seasonal russet-red colour.

Hydrangea paniculata ‘Bobo’ and ‘Silver Dollar’ are two to keep an eye out for as they don’t get as large as any of the other cultivars. ‘Bobo’ will stay at less than a metre in height and ‘Silver Dollar’ won’t reach higher than 1.25m but again I would prune both varieties hard in early spring to keep them good and compact with large flower heads. Both of these varieties, as they are relatively dwarf are suitable for growing in containers where others aren’t really as they get too big but do bear in mind that you will need to keep them well watered if growing in pots as they will dry out before your eyes.

Finally, if you are familiar with Hydrangea ‘Limelight’ another paniculata type but don’t grow it as it gets too big, reaching, as it can, over two metres in height, then go and treat yourself to H. ‘Little Lime’ which has all the beautiful attributes of ‘Limelight’, large, conical-shaped white flowers which start off green in colour, but as the name suggests, will stay at a much more compact and manageable size.

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