Our man in savannah: behind the plants at Dublin Zoo

The next time you find yourself grimacing at the damage that pigeons have done to your brassica plants, or shedding an angry tear for baby seedlings greedily devoured by slugs, spare a thought for Stephen Butler, Dublin Zoo’s curator of horticulture. A large part of Butler’s job is working out ways to lend the zoo’s various animal habitats, such as its newly-completed orangutan forest, its African savanna and its sea lion cove, a sense of horticultural realism without poisoning its inhabitants.

So if a particular species of animal naturally favours a rainforest habitat of undulating ground and trickling streams with lots of dense vegetation and trees, or another prefers open, grassy plains, then it’s Butler’s job to provide these.

The problem, of course, is that most animals, especially primates, are naturally inquisitive when it comes to the different plants that they share their world with, not just as possible food sources but also as things to play with, or climb, or use as scratching posts, or simply to uproot for the sheer hell of it. The result is that Butler has lost count of the plant species that have proved unsuitable.

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If you cut earlier fruiting raspberry canes down in summer after they have finished producing, you will be rewarded with more new shoots that will produce an extra-late crop of berries.

Purple willow

It’s only by acting on his horticultural instincts as well as consulting with fellow zoo gardeners around the globe that he’s discovered those that are. So, for example, if you have ever wondered why so many animal habitats at zoos have large stands of purple willow, it’s because its leaves are a natural source of salicylic acid, which gives them a bitter taste, thus preventing them from being eaten. “The gorillas did try them at first, but immediately spat them out,” says Butler, with evident pleasure at having outwitted these exceptionally clever primates.

Many of Dublin Zoo’s animal habitats are defined or enclosed by stretches of water that serve as secure, animal-proof boundaries as well as to underscore the naturalistic planting. Covering roughly a fifth of the zoo’s 70 acres, these lakes, moats and streams are fed by a natural spring dammed back in the 19th century. Planting and maintaining the edges of these waterways in a way that echoes nature, yet also serves the purpose of preventing erosion, is another of Butler’s responsibilities.

“Wild geese in particular were causing a lot of damage by constantly grazing the plants, resulting in soil erosion.”

Being nibbled on

In this case, the answer was mass planting with Libertia, an ornamental grassy plant often seen in Irish gardens and one of the few that can happily withstand being regularly nibbled on. With the water’s edges protected, the zoo’s streams and lakes now provide a magnificent habitat for a range of native wildlife.

Butler’s thoughtful planting uses many other decorative species that would thrive in most Irish gardens. An example is the planting around the perimeter of the zoo’s African savanna, designed to simulate the open, grassy plains enjoyed by grazing animals such as giraffes and zebras.

While none of the plants used are genuinely native to the real African savanna (the Irish climate would be entirely unsuitable), they do a fine job of suggesting its landscape. Among them is Ampelodesmos mauritanicus, a tall and exceptionally elegant evergreen grass with ornamental flowers that last right through the winter months and which would look right at home in a modern mixed border. So would many of the other grassy-leaved leaved plants that Butler has employed, including species of Schizostylis, Dierama, Agapanthus, Kniphofia and Moraea.

Bamboos have also been used to great effect throughout to give a lush, exotic feel. Again, these evergreen plants thrive in the damp cool of the Irish climate. Sourced from Peter Stam's excellent specialist nursery in Waterford, many are suitable for growing in Irish gardens, although Butler does sound a note of caution about the invasive tendencies of some species, including Sasa and Pseudosasa.

New plant trail

The value and importance of the plant kingdom to all forms of life, whether that's a huge elephant, or a tiny insect in need of food and shelter, is something that Dublin Zoo increasingly strives to highlight to visitors. Hence its new plant rail, marked by a series of informative signs that explain the significance of certain key trees and habitats.

One tells the story of the Wollemi pine, a species of coniferous tree that was believed to be extinct until rediscovered by an Australian National Park ranger in 1994. Another tells the story of the zoo's magnificent cedar tree, Cedrus deodora, which is nearly as old as the zoo itself, having been planted in 1850 when the rage for planting new and exotic species was at its height.

It's just one of the many trees the zoo will celebrate this weekend (Saturday 4th March-Sunday 5th March) as part of National Tree Week, with a series of tree walks, talks and wildlife-inspired workshops headed up by environmentalists and educators Éanna Ní Lamhna and Paddy Madden. They would love you to join in the fun. For details, see dublinzoo.ie

THIS WEEK IN THE GARDEN

If you need dozens of perennial plants for a new border or planting project but baulk at the cost, then consider propagating them by division from a couple of pot-grown specimens bought from your local garden centre. In particular, keep an eye out for slightly pot-bound specimens that will give you lots of excellent propagating material. Either tease the plant apart into several smaller sections or use a sharp knife to do so, then repot immediately and water well. Species suitable for spring propagation in this way include Astrantia, Phlox, Achillea, Sedum and Aconitum.

March is always a busy month for gardeners as regards sowing seed under cover. Increasingly gardeners are moving away from peat-based seed compost in favour of more environmentally acceptable alternatives. Sadly some of the peat-free products on the market aren’t great, but recommended brands include Klassmann (available from Fruithill Farm) and New Horizon (quickcrop.ie). Conveniently, both suppliers deliver by courier. To increase the chances of successful germination, bringing seed compost indoors for a few days prior to sowing so that it has time to warm up a little.

The traditional advice as regards pruning autumn-fruiting raspberries is to cut them back hard to the ground in late winter/ early spring in order to encourage the production of lots of new fruit-bearing shoots. But a useful and productive alternative technique that I picked up from gardening friend Nicky Kyle (nickykylegardening.com) is to cut only half the old canes back, leaving the rest to produce a much earlier harvest of delicious berries. If you cut these earlier fruiting canes down in summer after they have finished producing, you will be rewarded with more new shoots that will produce an extra-late crop of berries.

DATES FOR YOUR DIARY

Monday March 6th (2pm), Visitor's Centre, National Botanic Gardens, Glasnevin, Tree Books, Travel and Lore, this year's Tree Week lecture is by author and bibliophile George Cunningham on behalf of the Tree Council of Ireland.

Friday March 10th-Saturday, March 11th, The Garden House, Malahide, Dublin, Springtime Pruning and Colour; a practical gardening class with Marie Staunton, €15, pre-booking essential, see thegardenhouse.ie.

Saturday March 11th (10.30am-12.30pm), Bridgetown, Co Clare. There is a   hands-on garden visit to well-known organic grower Jim Cronin’s farm, see carmencronin.ie for details.