Thursday 24 August 2017

Diarmuid Gavin: Rhododendron rhapsody

Rhodos of all kinds excel in staging a stunning summer display

Rhododendron ponticum purple flowers
Rhododendron ponticum purple flowers

I've been lucky to see rhododendrons showing off their posies of plumes in a startling variety of disparate locations in the past 10 days. First, a place where one of its more robust varieties has given it a bad name (Rhododendron ponticum, regarded as an unwanted guest, rampaging wildly in a client's woodland); then on show at Malvern; in the wondrous gardens of Mount Usher, Co Wicklow, just minutes from my home; and, in my latest discovery, at the magnificent National Botanic Gardens, Kilmacurragh (shame on me as a Wicklow dweller for leaving it so long to visit).

Whether in search of rhodos or not, a visit to this last Eden is a must. The gardens, set in east Wicklow, were the centrepiece of an 18th-century estate that once covered over 5,000 acres. In the ownership of the Acton family for three centuries, they are now open to us all and are enjoying a magnificent resurgence under the curatorship of the very brilliant Seamus O'Brien.

The milder climate, higher rainfall and deeper acidic soils of this historic Wicklow garden provide a good counterpoint to the collections at Glasnevin. Both gardens have an association going back to 1854, when Thomas Acton inherited the estate and greatly benefited from the advice and support of Dr David Moore and his son Sir Frederick Moore, curators of the National Botanic Gardens in Dublin. Kilmacurragh provided a more advantageous situation for growing plants from the Himalaya and the southern hemisphere.

In 1996, a 52-acre portion of the old demesne comprising the house, arboretum, entrance drive and woodlands officially became part of the National Botanic Gardens of Ireland. By then the house was in ruins due to a series of disastrous fires and the following 10 years were spent rescuing valuable trees from a crippling tangle of cherry laurel, sycamore and this week's rogue, Mr Ponticum!

Generally, rhododendrons are a great shrub, producing startling displays and, given the right circumstances, relatively easy to grow. From very small to neck-craningly tall, there's a species and colour to suit all tastes.

R. ponticum (pictured) looks super now - rosy pink flowers adorning cloudy green mounds, set off by lush, dark green foliage - but it has a tendency to invade places where it's unwelcome, suffocating all that previously grew happily under the canopy of a woodland, and this has led to fears of mass invasion. It's hard to control: gangs of volunteers regularly gather to cut it out of the dells and dingles of sun-kissed Killarney National Park.

But it couldn't match the startling snowy trumpets of R. 'Cunningham's White', which topped the display at Mount Usher, a near neighbour of Kilmacurragh. Here, conditions were perfect for a masterclass of how to grab attention. Tourists from China, Japan, Germany and the US stared in awe as bumblebees hovered and darted busily, collecting pollen and buzzing with abundant pride.

I'd brought some Chinese visitors to show them what is, in effect, my back garden and the display didn't disappoint. From the awesome large leaves of R. sinogrande, a shrub that could make a lovely small specimen tree, to the acid oranges, scarlets and yellows, it was a dazzling sight. Somehow, rhodos get away with even the most garish of colours, possibly because they are calmed down by the beautiful foliage. In many cases they also have beautiful peeling plum-coloured bark, such as R. barbatum.

Mount Usher has acidic soil so it grows these and many other acid-loving plants with ease. But what do you do if your soil isn't acidic? The first option is to grow them in pots or even raised beds in an ericaceous compost. But there's an exciting alternative. In the last few years, a chance discovery of a rhodo growing happily in a lime quarry in Germany led to 'Cunningham's White' being successfully grafted onto this rootstock, known as Inkarho, which has since been used to grow many other rhododendrons. Its main advantage is that you don't need acidic soil: neutral clay soil is fine or up to a pH of 7. It also produces hardier shrubs, better able to deal with our harsh temperatures.

Whatever type you choose, don't plant too deep, as they are surface-rooting plants, and keep well watered during the first season especially (preferably with rainwater). Ideally, they like dappled shade and shelter.

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