British plant trials will help gardeners looking to replace blight-prone box, says Neil Ross.
Neil Ross looks at alternatives to box
Thinking Outside the Box is an attempt to inspire gardeners to move away from traditional box hedging.
I’ll never forgive Pete Bragg for the time we were walking home from school and he dealt me a well-aimed shove, sending me tumbling through an old lady’s hedge. Performed expertly, the classic shoulder shove can deliver a seriously meaty blow. I was completely taken unawares and crashed unceremoniously, like a top-heavy skittle, leaving a gaping hole in the manicured leafage.
Had my horticultural passions been more developed, I could have pointed out to the house owner how we were doing her a favour, ridding her of a good bit of dreadfully dull privet and providing an opportunity to rethink and replant, but as it was, she yelled and headed towards me at a pace across the lawn, brandishing a laundry basket. I leapt the hedge and ran.
A warmer welcome awaited at a recent visit to Wisley, the flagship garden of Britain’s Royal Horticultural Society (RHS). In the revamped walled garden, I was reminded of this childhood tumble as I inspected a set of finely trimmed but flimsy hedges of similar size to the one I had demolished all those years ago. Some would have made a perfectly springy landing pad for a wayward teenager – the likes of divaricating muehlenbeckia, for example – while others, such as several trendy new berberis cultivars on show in rainbow colours, would have put short shrift to any such tomfoolery with their wicked spines. This revamp of what was once an area devoted to immaculate and garish bedding displays is branded Thinking Outside the Box, and is an attempt to inspire gardeners to move away from traditional box hedging to less disease-prone alternatives.
Box ( Buxus sempervirens) has densely textured and small evergreen leaves that don’t look ragged after a trim. The growth rate is not too vigorous either so you can, in cooler parts of the world, get away with a single trim in the year (although two is normal). But there doesn’t seem to be a
country in the world that has not succumbed to the super-fast defoliating box blight ( Cylindrocladium buxicola). And now – in Europe at least – there is another exotic invader, the box tree caterpillar ( Cydalima perspectalis) set to cause even more woe to the world’s favourite hedging plant.
Some gardeners have turned to the dwarf holly Ilex crenata. It looks like box but is even slower growing – and the RHS have found its performance patchy in the sandy soils at Wisley. Personally, I find it rather stiff and brittle too, so if you have boisterous kids or are just clumsy stepping over it to prune the roses, branches can snap off. I was surprised there were no sarcococca shrubs on show or dwarf euonymus varieties on trial because I’ve seen these make good little evergreen hedges, but it’s nice to see that, in their search for a springy and tough alternative, the RHS has turned to several Kiwi plants.
The range of mountain totara ¯ ( Podocarpus cunninghamii) cultivars that was on show was impressive, from ‘Country Park Fire’ to ‘Young Rusty’ – so new I’m not certain they have been released in New Zealand yet! Many have interesting purple or bronze winter foliage effects and strikingly bright new growth in spring, and they certainly take well to clipping. In appearance, t¯otara looks more like yew than box but that can be no bad thing; it’s a mystery how seldom we see yew used for hedges.
One strength of box is the fact that it can be maintained as a small hedge below knee height, so I think the choice of some medium-sized pittosporums and corokias by the RHS will prove a challenge to keep so small in stature.
Black matipo ( Pittosporum tenuifolium) needs a lot of clipping to keep it tight and neat; that might be a real drawback. We have some superb dwarf varieties already, such as purple ‘Tom Thumb’, green ‘Golfball’ and greyish ‘Humpty Dumpty’ named in 2006 by McKechnie Nurseries in Albany. These would all make small, informal hedges but you might struggle to coerce them into crisp geometric shapes. Corokias are susceptible to wet soils and tend to have upward-thrusting foliage which is never amenable to being clipped low, but the cultivars on show looked to be doing well – in these early stages, at least.
The design is based on Elizabethan knot gardens with the hedge tops cut to look like the different varieties are weaving under and over each other in a lattice effect. Curator Matthew Pottage intends to keep the experiment dynamic by editing every few years; digging out the underperformers and swopping them with new ideas.
The test of a hedge comes with time, when repeated clipping, wear and tear, and plants flopping and shading the sides take their toll. But full marks to the RHS for facing this problem with such enthusiasm and flair – and flying the flag for our amazing flora at the same time.