Gardening

Singing the praises of wall shrubs for year-round structure and heft

Think also about fruit trees like apple and pears that can be gently manipulated to grow in a variety of shapes, including espaliers, fans and cordons

Magnolia grandiflora, commonly called southern magnolia or bull bay, is a medium to large evergreen tree

Fionnuala Fallon's face
Fionnuala Fallon
Mon Apr 29 2024 - 05:00

This week’s Q&A has prompted me to sing the praises of wall shrubs, that group of plants that usefully straddle the common ground between true climbers (plants with lax stems that twist and weave their way upwards, using walls or the branches of other plants as a scaffold) and traditional woody ornamental shrubs.

Trained against a wall or sturdy fence by dint of thoughtful pruning and a system of lateral galvanised wires, to which their young branches are gently tied, they can be used to give a valuable sense of year-round-structure, heft and permanence to even the tiniest outdoor spaces. Wall-trained shrubs also offer the opportunity to grow species that might otherwise be too large and sprawling for a small garden, as well as those that need a particularly sheltered spot, with protection from damaging frosts and cold winds.

Examples that come to mind include the magnificent Magnolia grandiflora, or bull bay as it’s commonly known. Blooming in early summer, this glorious species is prized for its huge, pale, fragrant, cupped flowers and giant evergreen leaves, the underneath of which are covered in the softest brown fuzz.

[ Your gardening questions answered: How should I plant up my new flower beds? ]

Planted as a normal freestanding specimen, it will eventually become a sizeable tree and needs plenty of horizontal space to flex its muscles, slowly reaching a height and spread of up to 15m. But a wall-trained specimen can be kept much more compact, and is a magnificent sight when grown neatly against a high sunny wall where the latter acts as a simple but effective storage heater, as well as the perfect backdrop to its statuesque beauty.

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This outstanding species of magnolia is just one of many kinds of large ornamental evergreen shrubs that are eminently suitable for training vertically against a sunny wall or sturdy fence, and which will thrive in the additional warmth and shelter that it offers. Others include the lovely blue-flowered Californian lilac (Ceanothus ‘Trewithen Blue, Ceanothus ‘Concha’); sweetly-scented myrtle (Myrtus communis); the white flowering tree anemone (Carpenteria californica); flannel bush (Fremontodendron); the deliciously scented, pale-flowering Osmanthus delavayi and Osmanthus burkwoodii; vanilla tree (Azara microphylla); silk tassel bush (Garrya elliptica); the variegated Euonymus fortunei ‘Silver Queen’; sweetly scented Itea ilicifolia which is prized for its dangling green flower racemes (imagine a very refined version of amaranthus); and cape fuchsia or cape figwort (Phygelius capensis), a South African sub-shrub that produces its dense clusters of tubular salmon-orange flowers in summer.

These ornamental evergreens shrubby species aside, there is a host of deciduous shrubs suitable for wall training which similarly flourish in the sheltered conditions offered. Many of the best are hardy, early-flowering species whose blossom is shown to best effect when grown this way.

Examples include the aristocratic shrub known as wintersweet or Chimonanthus praecox, whose intensely-perfumed waxy flowers appear along its bare branches in late winter; ornamental quince (Chaenomeles speciosa), whose clusters of shallow, saucer-shaped spring flowers can be white, pink, scarlet or orange depending on the variety; and the elegant, acid-loving Stachyurus praecox. Given skilful pruning and training, the same is true of witch hazel (Hamamelis).

Of course sunny garden walls also provide the perfect growing conditions for training many kinds of fruit trees vertically against it, that can be gently manipulated to grow in a variety of shapes that includes espaliers, fans and cordons. Apples, pears, peaches, and apricots can all be treated in this way, a truly space-efficient and decorative method of incorporating fruit trees into small gardens so that they are as productive as they are pretty. The same goes for cherries and plums which will happily grow against a shady wall or sturdy fence. Just bear in mind that unlike ornamental shrubs, it’s generally best to start with a young fruit tree that’s already been partially trained rather than what’s known in the business as a “maiden” tree. The former are more expensive (a lot of time and work goes into their formative pruning in the first few years of their lives), but will be quicker to produce fruit as well as much easier to subsequently train and keep in shape.

Once upon a time these kinds of wall-trained plants were a common sight in chic town gardens, their artful growth the discreet stamp of a good gardener. But with the exception of the thorny, brilliant-berried, ubiquitous pyracantha, they’ve somehow fallen out of favour in recent years. Part of the reason for this is because of a lack of confidence on the part of gardeners when it comes to the actual process of pruning and training them. There can also be concern – generally misplaced – that wall shrubs and trees will eventually damage the structures against which they’re grown.

In fact, they pose much less of a risk than self-clinging climbers such as ivy and Hydrangea petiolaris, whose probing aerial roots can gradually find their way into small gaps into any crumbling mortar or pointing work between bricks or blockwork. But anxious that we might do the wrong thing, we avoid them, which is a great shame.

That said, a thoughtful, carefully-timed annual pruning regime is required to produce and maintain a wall shrub or tree with a well-balanced framework of branches that performs at its floriferous and/or productive best. Get it badly wrong and although it will eventually recover you might remove some of next year’s flowering branches or end up with a slightly misshapen plant. Neglect to do it at all and you’ll end up with a plant that eventually becomes too big for its boots.

When to prune? As a general rule, shrubs and trees that flower on the previous season’s growth (typically species that flower in winter, spring or early summer) should be pruned just after they’ve finished flowering. But plants that flower on the current season’s growth (typically species that bloom in mid or late summer or in autumn) are usually pruned in late winter or early spring.

Formally trained fruit trees aside (these need a slightly more carefully considered pruning regime) you’re aiming to create a plant with a well-proportioned, permanent framework of branches that grow comfortably along the wall. To keep it space-efficient keep its side shoots short by cutting them back at pruning time to within two-four buds of this permanent woody framework. To keep it healthy give your wall shrub a really good soil enriched feed with plenty of organic matter and then mulch around the base each spring with some well-rotted manure and a handful or two of organic fertiliser. It truly is as simple as that.

This week in the garden

Well-established seedlings/young transplants of many (but not all) species of flowering annuals and perennials benefit greatly from the technique known as “pinching”, where the soft growing tip of the plant is nipped out using your index finger and thumb. This encourages the development of plenty of flowering side shoots, resulting in a much bushier and more floriferous plant. Examples of ornamental species that benefit from pinching include cosmos, tagetes, calendula, nicotiana, achillea, dahlia, fuchsia, and chrysanthemum.

Sow seed of fast-growing half-hardy vegetables such as courgette, pumpkin, squash and French beans on a sunny windowsill or frost-free glasshouse for transplanting outdoors into their permanent positions in the garden or allotment at the end of May.

Dates for your diary

Today, Saturday April 27th (1.30pm-4.30pm), Cabinteely Community School, Johnstown Road, Cabinteely, Dublin 18, DHV73, the Alpine Society’s annual show & plant sale with a wide range of beautiful plant exhibits and plant stalls;

Tomorrow, Sunday April 28th, (from 11am) Ennis Showgrounds, Co Clare, Clare Garden Festival celebrates its 10th year anniversary with a line-up of expert speakers that includes Kitty Scully, Jim Cronin, Carl Wright, Michael Kelly, Jo Newton and Lynn O’Keefe, plus demonstrations, and plant, craft and food stalls, see claregardenfestival.com

Sunday May 5th (10am-4pm), RHSI Russborough, Blessington, Co Wicklow, the annual RHSI Russborough Garden Show takes place. The line-up of expert speakers includes Paul Smyth, head gardener at RHSI Bellefield; Conall O’Caoimh of Ardán Gardens in Howth, Co Dublin; Maurice Parkinson of Ballyrobert Gardens & Nursery; Youtuber and Ireland AM garden contributor Niall McAuley; chef Catherine Fulvio and representatives from Festina Lente in Bray; plus demonstrations, workshops, children’s entertainment and plant and food stalls, see rhsi.ie

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