Diarmuid Gavin: Heavenly hydrangeas
One of my very favourite gardens is a city plot planted solely with these pretty shrubs
It was devised solely to slow down traffic on what was a notoriously busy road - now Lombard Street in San Francisco is home to one of my favourite gardens in the world. Its residents came up with the idea of planting a garden and having the cars crawl through it (pictured inset), so with the help of those hydrangeas, the garden of 11 tight hairpin bends emerged. Today, cars drive especially to see these wonderful late summer flowering shrubs.
For flower power it's hard to beat hydrangeas. Although sometimes labelled as old-fashioned, as a cut flower they are enjoying something of a hipster revival. And for millions of gardeners like me, they remain a favourite. Any gardener with hydrangeas will tell you that they are besieged by endless questions and queries: from how to prune, to why blue ones turn pink, and issues with flowering.
The name hydrangea comes from the Greek, meaning water vessel. The species originated in south and eastern Asia (Japan, China, the Himalayas and Korea) and the Americas, and was first introduced to these islands in the 18th century.
Their colour ranges from white through pink to the much-admired blue. The Portuguese island of Faial in the Azores is also known as the Blue Island due to the abundance of blue hydrangeas growing there. But many gardeners in Ireland have been disappointed after trying to recreate that look by planting beautiful blue hydrangeas, only to find them turning pink the following year.
It's aluminium sulphate which makes the petals blue, and this is only available for uptake by the plants' roots in acidic soil. If you don't have the right soil, a good way to ensure ideal conditions is by growing the plant in a container where you can use an acidic compost and occasionally top it up with aluminium sulphate.
A simple soil test from your local nursery can help determine your pH level, which will determine your hydrangea colours. Generally, soil with a pH below 6.0 (acidic soil) will produce blue hydrangea blooms, and a pH above 6.0 will produce pink hydrangea flowers. Depending on your preference, you are able to change the colour of your hydrangea blooms to fit your desired colour.
Hydrangeas will grow well, even if ignored, but they can become a bit leggy if left unpruned. Many small front gardens are dominated by specimens that have been left to their own devices.
Mophead and lacecap hydrangeas are the type most commonly planted and will usually only require their old flower heads to be removed, cutting back to a pair of healthy buds. It is generally wise to leave this until spring, as the old flower heads will give the more tender buds some protection from winter frosts.
To keep the plant producing fresh stems, remove two or three older stems completely. If you have to chop back to bring the plant back to a manageable size, you will forfeit the flowers that year, but they'll return the following year.
Hydrangea Annabelle tends to be a favourite with her voluptuous domes of white flowers. But vanilla fraise, a paniculata hydrangea with cones of white flowers that age to a strawberry pink, is also wonderful. Last year I also planted hydrangea aspera macrophylla in my garden. This will grow into a large shrub with big, felty leaves and beautiful lacecap flowers, pure white on the outside surrounding a mauve centre. There's also a climbing hydrangea (hydrangea petiolaris), which will happily grow up a north or east-facing wall, and best of all doesn't need any supports as it clings to the walls with its aerial roots.
Like a lot of climbers, it can take a few years to really settle into a new home, but be patient - lots of growth will be happening underground as the plant spreads it roots and prepares to climb skywards.
Ideally, plant hydrangeas in moist, well-drained soil and in dappled shade - avoid dry, sunny places. A bit of shelter is good, especially from biting-cold easterly winds that can damage flower buds. That said, they're excellent maritime plants, having good tolerance to salty spray.
For the first year or two after planting and during any drought, be sure hydrangeas get plenty of water. Leaves will wilt if the soil is too dry.
If your soil is rich, you may not need to fertilise hydrangeas.
If your soil is light or sandy, it's best to feed the plants once a year in late winter or spring. Too much fertiliser encourages leafy growth at the expense of blooms.
How to Prune a Hydrangea
• Mophead types have the big snowball-size blooms. Along with lacecap hydrangeas (pretty flowers almost hanging down from a flat centre of tiny blooms), they should be pruned after the flowers fade.
• Flower buds actually form in the late summer and flower the following season, so avoid pruning after August 1.
• Only cut away dead wood in the autumn or very early spring.
• To prune, cut one or two of the oldest stems down to the base to encourage branching and fullness.
• If the plant is old or neglected or damaged, prune all the stems down to at the base. You’ll lose the flowers for the upcoming season, but also renovate the plant for future years.
• It’s best not to deadhead the faded blooms on the big mopheads. Leave them over winter and cut them back in early spring to the first healthy pair of buds.
• It’s fine to deadhead the lacecaps though — cut down to the second pair of leaves below the flower head.