Architectural And Exotic Plants

This is an excerpt from the Book called “New Classic Gardens  by Jill Billington. Continue reading to learn more about Architectural And Exotic Plants, thanks to the author.

Architectural & Exotic 

Modern formality may be orderly but it is certainly not predictable.  One of the charms of today’s designs is that there are fewer preconceptions as to how a garden should look, so native plants with strong form as well as exotic-looking subjects from sub-tropical climates are frequently included in the layout to add an element of surprise and challenge.  You may need to choose a reliably hardy form for a protected environment or use more tender species in containers that are brought outdoors only for the summer.  Check with a local nursery if in any doubt about a plant’s suitability for your climate. 

Architectural and exotic plants can be used singly, or they may be planted in linear regiments or as a group.  Used as soloists, they draw the eye and could be the focus of a minimalist garden.  They may emphasize layout by being planted in lines, while in a group they can add drama to an otherwise humdrum, easily maintained geometric background. 

Architectural plants  

The all-important atmosphere of a garden is greatly affected by the types of plant selected, and plant form speaks volumes in a formal setting.  Those plants that grow naturally with a clear outline create shapes and silhouettes which have great character; naturally large-leaved examples include the frost-tender silvery Melianthus major for sun and rodgersias for shade.  Where there is a lot of detail in a garden, these shapes help to establish a focus which draws the eye. 

Architectural plants
Architectural plants  

The shape of a plant often determines how we use it; its inherent formality may be exact and geometric, as in the Irish juniper (Juniperus communis’Hibernica’), or studiedly asymmetrical, as in the best forms of Japanese maple (Acer).  Vertical outlines catch the eye whichever purpose they serve and sword-like foliage is just as focused.  Stiff sword-likes shapes such as that of New Zealand flax (Phormium tenax) will always stand out.  The sword leaves grow from the base of this plant, fanning out widely, so it needs space.  In its native country, the smooth grey leaves with tall panicles of dark plum-red flowers reach 3m (10ft).  It benefits from a mild climate, where it will reach its natural ultimate height, but when less well suited the height may be reduced to about 1.8m (6ft).  There are also variegated and reddish forms, as well as some smaller cultivars like the brown-red P. ‘Bronze Baby’ which is only 45-60cm (18-24in).  Because of their uncompromising structure, all phormiums suit formal gardens.  Among the smaller P. cookianum cultivars there are some, like the 1.5m (5ft) tall P.cookianum subsp, hookeri ‘Cream delight’, whose reflexed outer leaves shine in the light, creating a softer look. 

Some crocosmias and flag irises have similarly tall, elegant, lanceolate foliage with knife-points, but they are deciduous and their bright green colouring has a less dramatic effect than the grey-greens and purples of the phormiums, so they merge rather easily with other plant leaves. 

Foliage plants for shade 

Formality in the shaded garden can be achieved using a framework of clipped shrubs with some audaciously large-leaved plants.  Shapely foliage is an asset, particularly when it is evergreen.  Architects choosing to flatter their town houses often use the easy-going evergreen shrub Fatsia japonica and its variegated form F. japonica ‘Variegata’ (both 1.5-4m/5-12ft), because they have large, glossy, palmate leaves that look good against wall even in dense shade.  The admirable acanthus also earned respect from architects a long time ago, in ancient Greece, as can be seen on the capitals of Corinthian columns.  The statuesque Acanthus spinosus, almost 1.5m (5ft) when its flower spikes are fully fledged, will do well in light shade or full sun.  Its deeply divided, sharply pointed foliage is magnificent but this plant must have space.  These large-leaved plants make a strong statement wherever they are. 

Most plants with large leaves are best suited to shaded, damp areas where the rate of evaporation from their leaves is slower.  In temperate gardens rodgersias, rheums, cimicifugas and ligularias have great foliage presence; their large leaves are either rounded or jagged and they have tall flower spikes in summer.  In the formal country garden, foxgloves (Digitalis) look good rising from groundcover comprising large hostas (like H. ’Big Daddy’), bergenias (like B. ‘Ballawley’)and the invasive, massive-leaved Trachystemon orientalis, all of which, with their overlapping leaves, create formal effects and can serve the need for low maintenance. 

Shapely plants for sun  

For flowering as well as foliage interest in hot spots there are some rigidly erect herbaceous plants, like the brilliant columns of kniphofias, rising from knife-pointed leaves, or the huge foxtail lilies (Eremurus robustus) that grow vertically to a height of 2.5m (8ft) and more.  Plants like these may be used in summer as sentinels, marking either side of an entrance, or will make a random Manhattan –like skyline of white, pink, cream or yellow.  Other bold temperate plants with skyward ambitions include massive hybrid delphiniums, although these do need staking; some grow over 2.5m (8ft) and are a pathetic sight when snapped by the wind.  The older Belladonna Hybrids are shorter, up to 1.5m (5ft), but they are similarly aspirant and produce successive spikes through to late autumn.  All enjoy free-draining, neutral soil. 

The sharp, silvery magnificence of the cardoon (Cynara cardunculus) requires sunlight and space to accommodate a circumference of 1.8m (6ft).  Macleaya microcarpa ‘Kelway’s Coral Plume’ requires less space as it grows more vertically, attaining 2.1m (7ft).  The large lobed leaves are dove-grey with white undersides and the flowers are fluffily fine, contrasting with the smooth, flat leaves.  This plume poppy is one of the few large-leaved plants that will grow in direct sunlight, apart from those sub-tropicals that live in high humidity; free-draining soil is important.

Shapely plants for sun
Shapely plants for sun

Two appropriate biennials should be mentioned here-one is the silver-grey, lethally spiny Scotch thistle (Onopordum acanthium), which grows to a height of 1.8m (6ft) by the second summer.  The other, which has contrastingly luminous grey woolly leaves, is the giant mullein (Verbascum olympicum) which reaches over 2m (6ft 6in). 

Exotic plants  

Contemporary designers of formal gardens often look to ‘foreigners’ to provide a dramatically different summer look and they experiment with these tender exotics to create a garden magnificently out of context with its surroundings.  By ‘exotics’, I mean plants that have dramatic foliage and extravagant form.  They usually come from sub-tropical parts of the world but can often be grown successfully in cooler climates given a sheltered, warm position where the soil is rich and will not dry out but drains freely.  They are often faster-growing than the smaller-leaved plants native to temperate climates and can take over in a competitive situation. 

This is not a modest or sentimental garden style-it is bold and exciting.  In the modern garden these exotics can be ravishingly different, brilliantly coloured and powerfully foliaged.  The hardiest ones, like the fan palm and dwarf fan palm (see opposite), will set the skeletal form of a scheme, used either as an individual focus or in regimented lines, like the orange trees of Versailles.  More fragile specimens like daturas may then be slotted in for the summer season, provided they are grown in containers that can be taken back indoors for winter. 

Some spiky-leaved yuccas are hardy, such as the trunkless Yucca filamentosa, surviving at temperatures of -10°C (14°F) , but others are less so, like the neatly compact, stemless Y. whipplei, which should be grown only in the warmest areas and well protected, if necessary, from cold winter rain.  And Y. gloriosa’s massive 60cm (2ft) long flower panicles carry creamy-white hanging bells over a trunk with dagger-like leaves.  The magnificent grey lanceolate foliage of yuccas is not be trifled with, so these are not plants for the family garden.  A yucca-like plant, Beschorneria yuccoides, must be grown in a sunny position where it may bake in summer, but it needs some protection from wind, like a south-facing wall, and well-drained soil.  Its red flower panicles are a rewarding sight.  The spiked foliage of cordylines is less threatening but every bit as stylish.  Cordyline australis, the hardiest species, survives at- 5°C ( 23°F),  gradually reaching over 15m (50ft), but also consider C. indivisa, with its large crown slowly growing to 3m (10ft) in warmer sites.   

From the really arid areas of the world come the extraordinary shapes of cacti.  These reservoirs of water grow into tough, distinctive fleshy forms.  Most are unsuitable for transplanting but some of the prickly pears (Opuntia) from North America will adjust to growing in areas that are guaranteed frost-free.  But unless you have really hot, dry conditions, the choices will be limited.  In desert heat, wonderful shapes and colours are to be found, like the little rounded Cereus species and Echinocactus, contrasting with the prickly pears.  They are in the colourful company of aloes, like the 2m (6ft 6in) tall, flowering Aloe arborescens, agaves like Agave Americana ‘variegata’, wickedly sharp and with a height and spread of 2m (6ft 6in), or aeoniums, such as Aeonium arboretum ‘magnificum’, which is 60cm (2ft) tall but 1m (3ft 3in) wide, with frost-hardy Zauschneria californica ‘Glasnevin’, a clumpy perennial with tubular scarlet flowers and spurges such as Euphorbia seguieriana, a bushy, frost-hardy plant of 45cm (18in) with glaucous foliage and terminal flowers that are acid-yellow. 

Palms are classified as sword, feathered or fan, which is an indication of their distinctive shapes, but most suit only gardens where they are protected from frost by glass.  The Chinese fan palm Trachycarpus fortunei will survive in mild areas if the temperature is no lower than -5°C (23°F); it has a tree-like habit, growing to about 8m (27ft), with 1m (3ft 3in) wide fans on every stem.  Chamaerops humilis, the dwarf fan palm of 1.5m (5ft) height and spread, is deal for smaller gardens; it is frost-tender, needing a minimum temperature of 7°C (45°F).  Growing these palms alongside grey-foliaged plants and an evergreen Euphorbia characias subsp. Wulfenii, with its branches of crowded narrow leaves forming a rounded shrub 1.2m (4ft) wide, makes for a Mediterranean style of formality. 

Exotic plants
Exotic plants

More exotic foliage effects come from bamboos like Phyllostachys nigra, with ebony canes, growing to approximately 3.5m (11ft) in cooler climates or the huge P. viridiglaucescens (7.5m/25ft) which survive at -20°C (-4°f).  There are smaller ones like the pygmy bamboos that are good for neat edging but many are very invasive.  Even in temperate climates you can have success with a banana (Musa basjoo), which needs a wide space to reveal its assets.  It will not produce fruit, but the magnificent paddle-like leaves may be 1m (3ft 3in) long; provided it is wrapped in horticultural fleece for winter, the banana will ultimately reach 3-5m (10-15ft) with a diameter of 2-2.5m (6-8ft).  And from Tasmania come the tree ferns (Dicksonia antartica), with their low, wide canopy of fronds now being grown in surprisingly cool areas, though they are half-hardy to frost-tender and prefer humus-rich, moist soil.  You can buy short trunks from the garden centre but eventually tree ferns grow to 10m (30ft) and, with their summer canopy, will be up to 4m (12ft). 

Brilliant colour among exotics can be achieved with the flowering cannas from South America, crinums from tropical Asia, Aloe aristata and Ricinus from tropical Africa, daturas (Brugmansia) from the West indies, Eucomis from South Africa and ginger lilies (Hedychium) from India.  In temperate climates, these can be grown indoors and put out in summer where, among the more modestly coloured northern plants, they will stand out and instantly add drama to the garden. 

Consider the siting of exotics carefully, for example placing them in dappled light where necessary or against walls in full sun, but avoiding east-facing walls because the early morning sun will thaw frosted buds and flowers too quickly, ‘burning’ them brown.  Be sure that the moisture level is constant or that free drainage is available as needed.  Protection with horticultural fleece in winter will widen the scope of sub-tropical species that can remain outside or you could contemplate moving such plants indoors for winter if you have room.  Straw, bracken or even old newspapers can also be used to protect tender plants; sacking or hessian strips will hold them in place but they will not be very attractive in winter.  There are other methods of wind protection, such as setting out temporary screens of fine-mesh nylon netting or, more attractively, by installing woven hurdles of hazel or willow around the plants.

Architectural And Exotic Plants
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