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Architectural plants are the elegant permanent residents of your garden that give it it's "backbone". If you consider your garden as a room, then the architectural plants are the large permanent residents, the "furniture" while other shorter-lived and smaller plants are the pictures and ornaments. Whether a plant is "architectural" is pretty much a matter of opinion and so this is a somewhat arbitrary group.
There are some qualifying traits however that a plant should have for inclusion, in particular it should have a strong and distinctive shape, both of the leaves and of the overall growth pattern. It is also helpful if the plant is evergreen, or with a distinctive winter presence - bark coloration, shape of branches for instance so that your garden doesn't become dull in the winter. By definition architectural plants tend to be fairly large.
Arguably all trees should fit into this category and in the summer they probably do, what is needed is year-round interest and not so much of a "blobby" shape.
The plants featured are recommended as they are reliable in most soils in most regions and are widely available.
C - Climber P - Perennial S - Shrub T - Tree
Abies koreana - Korean Fir T
Conical conifer with darkish green leaves. Produces purple-blue cones from an early age which are very decorative. A well shaped and proportioned tree, to 30ft tall and 20ft wide.
Acer palmatum, Japanese Maples - assorted T
The archetypal Japanese tree (other than bonsai) usually bought as a small specimen 1-2ft tall. Not tolerant to being exposed to cold, wind or full sun and best grown initially at least in a container so you can move them about to find the best position. They don't like chalky soils preferring it on the acid-side. Numerous cultivars available, one of the commonest (and cheapest) being "atropurpureum" which needs positioning carefully as it can appear rather dark and dense. The "dissectum" cultivars are very beautiful with finely cut leaves. "Aureum" has plainer shaped leaves but a lovely bright yellow color. "Sango-kaku" (senkaki) has bright coral-red winter shoots with yellow autumn leaves.
Aucuba japonica - Spotted or Cuban laurel S
Evergreen shrub, with glossy leaves to 8" long spotted yellow. Plants are either male or female, females have bright red berries in autumn. Tolerant of quite deep shade and indeed requires some shade to be really happy. Will grow in difficult situations and tolerant of dry soil. To about 10ft high and wide but easily controlled. Frequently sold as three or four rooted cuttings in a pot, separate them and you instantly have more plants!
Bamboos S / P
A large and varied group of graceful grasses which contrary to popular belief are often hardy and not invasive - it does depend on temperature though. In colder climates they are fairly slow growing and the length of the stems is connected to the extent of the root system. So if your young plant doesn't produce 8ft high canes immediately, give it a chance to establish. In the warmer southern states however, you need to be very careful of what you buy if you don't want canes growing to 50 feet or more.
Bamboos are evergreens and not affected by any major pest or disease in this country (there's little chance that panda's will start eating the emerging shoots). They are not always able to cope with exposed windy conditions which often makes them look a bit tatty and threadbare. they all prefer dampish conditions and won't withstand being baked by the sun with little moisture available.
*Arundinaria nitida (also known as Sinarundinaria nitida or Fargesia nitida) - fountain bamboo, is a handsome one with dark purple-green canes and dark green leaves, to 15ft high by 5ft wide. Arundinaria murieliae (Sinarundinaria or Fargesia murieliae) - umbrella bamboo is similar but more, well, umbrella-shaped. Yellow-green canes at first turning yellow with age. Phyllostachys nigra - black bamboo is particularly striking with canes that start green but then turn black in the second or third year 10-15ft high by 6ft wide.
Bamboos, particularly large specimens are not cheap but are fairly easily propagated by division when grown in containers, keep moving them on to bigger and bigger pots (i.e. the opposite to when they are grown in a container as their final home) which encourages them to spread, before taking them out and splitting into several plants.
* Bamboos have undergone a taxonomic review in recent years, meaning that their ancestry and relationships with other plant types has been update in the light of new evidence and discoveries. The knock on effect to this is that many bamboos have been renamed and are still often to be found as the same species under two totally different Latin names - such is the price of progress.
The birches are admirable trees for small gardens, some types can grow tall (eventually to 50ft or more), but they tend not to spread very far and have an open canopy that gives a dappled shade, a lovely effect. They need an open sunny situation. Leaves turn gold in fall, flutter in the breeze as briskly as quaking aspen.
The native silver birch Betula pendula is a popular choice, but the bark is rather rough and splits with dark patches forming with age, go for named cultivars such as "Dalicarlica" / "Laciniata" or "tristis" if you can find them. I prefer the Himalayan birch, Betula utilis "jacquemontii" (usually sold as Betula jacquemontii) or the paper birch, Betula papyrifera. Both have a smoother, brighter bark than the native species and are fairly easy to find.
If you have more space, birches can be planted as a triangular group of 3 about 3 feet apart. You tend to get a similar canopy as if a single tree was on its own, but 3 times the trunks and bark which is the main feature. Zones 2 to 7
Choisya ternata - Mexican Orange Blossom S
Glossy evergreen shrubs that comes in two main types grown either for wonderfully fragrant white flowers in summer (and often again in autumn) with green leaves, or for vibrant yellow leaves in the variety "Sundance" which unfortunately rarely flowers. "Aztec Pearl" is a flowering green variety with leaves that are more delicately cut.
Often described as having "fragrant foliage", I think beauty is definitely in the nose of the beholder on this one. Probably not so bad in small doses, and the smell is only released when the leaves are rubbed. The flower scent however is exceptional. To about 6-8ft tall and wide. Best in sun.
Cordyline - Cabbage palm S
Larger outdoor versions of the dragon-trees and ti-trees often grown as houseplants. Evergreen woody tree-like shrub or perennial. Can grow to 10-12ft or more in parts of the country that have reliably mild winters.
These are not fully hardy, so don't push it too far, plant them in sheltered areas away from strong winds and with the protection of a wall if possible. They can be helped over the winter by tying the leaves together with some soft string in the late autumn to protect the tender heart of the plant from frosts.
Cortaderia selloana - Pampas grass P
Pampas grass is a big plant 6ft tall by about the same wide with flower panicles to 10ft, so plant it slap bang in the middle of a small lawn and it will look completely overwhelming. Maybe people seem to think "oh its only a grass, it can't be that big".
Best planted at the margins of a garden or at the back of a mixed border unless you have great expanses of lawn. If you can, plant it so that the sun sets behind it when viewed from your house or usual garden viewing place and you could well come to love it deeply. It's very resilient and an easy plant to grow, try it in a difficult area where its natural vigour may well allow it to thrive while the difficult conditions will keep it smaller than normal size (but with less flower panicles).
Eucalyptus spp. esp. - gunnii - Cider Gum T/S
Eucalypts are a genus of trees that if left to their own devices that will go to 50ft +, if they're happy. However, don't be too alarmed. What you need to do is treat a Eucalyptus as a coppice stool. Let the plant get established for one or two years and then in Feb / March you cut it down to about 4-6" above ground level. This encourages it to throw out new shoots from just below the cut point. The plant will then provide you with lots of very attractive glaucous blue/green juvenile foliage that can grow up to 6ft from ground level in a season. It's also reputed to keep midges and mosquitoes at bay, so plant it near the patio.
A very beautiful foliage plant, excellent against rather dull fences and as a contrast to other leaf colors and shapes. Tends to be a bit fussy about position. Likes to be well drained so incorporate lots of sharp sand and / or pea shingle when planting it and only plant in full sunshine, otherwise 6ft growth a year becomes 6mm.
Euphorbia mellifera - Honey Spurge S / P
The evergreen Euphorbias sound as dull as ditch water from a simple description of their insignificant small flowers surrounded by greenish or yellow bracts. They manage however to be one of the most striking groups of garden plants and one of my favourites (hence three entries!). Somehow with a restricted palette of shades of green and yellow, they manage to "glow" in the garden, a definite example to the more gaudy garden residents that "less is more".
E. mellifera is one of the larger members of the group and is well placed at the back of the border. It has vibrant apple-green leaves and the flowers while not being particularly striking, have a probably unique scent of honey. An excellent addition to any garden. To 8ft tall and wide. Best in sun tolerates some shade, not fond of exposure so molly coddle it a bit if you can.
Euphorbia myrsinites P
Completely different habit to E. mellifera above. A prostrate creeping plant with blue-green leaves, yellow "flowers" in spring. 4" tall and spreads to about 18", a succulent so needs reasonable drainage, goes well with spiky plants or against gravel / rocks etc.
Euphorbia wulfenii S
Bluish green leaves to about 4ft tall. Particularly bright green-yellow "flower" heads in spring. Well known and deservedly so. Reputed to emit a coffee scent.
Fatsia japonica - castor oil plant S
A large plant with large bright glossy leaves up to 36" long in mature specimens. Chiefly a foliage plant, but also produces long lasting white flowers as a bonus which are followed by masses of black berries. Fits into many different styles of garden, but best in formal or jungly / tropical types. Grows in sun and also in quite deep shade. To 12ft by 12ft but not for ages.
Gunnera manicata - Giant rhubarb P
The common name sums it up very well, although this one is from the South American jungles and inedible. The leaves are enormous, up to 6ft across borne on prickly stalks to 8ft long. It is really a bog plant and needs moist conditions, if you think you might be able to accommodate its requirements and size, then little else will get the same WOW! effect, I love them. Also notable in that it dies back totally in winter (protect the base of the crown with a thick manure mulch) and so all of this fabulous growth happens from ground level each season. To 8ft tall and 10-12ft across.
Hedera - ivy C
e.g. Hedera canariensis - Canary island ivy - variety, "Gloire de Marengo" - Large shiny variegated leaves with a jungly feel. Not as hardy as most Ivies you see (which are often as tough as old boots), so benefits from some shelter. Grow as a climber up a wall or use as ground cover, pretty vigorous in both situations. To 12ft.
Useful for their evergreen foliage and winter color provided by berries and / or variegated leaves. Slow growing and usually only available as smaller specimens as they don't take too kindly to being moved. Will tolerate shade, especially the darker-leaved forms, variegated types require sun to bring colors out to the optimum. Hollies are usually either male or female and only the females have the berries, but they need a male to achieve this! The naming of varieties doesn't help the situation however;
Ilex aquifolium "Silver Queen"
- variegated green / cream, male.
I. aquifolium "Mme. Briot" variegated green / yellow, female, red berries.
I. aquifolium " J.C. van tol" - self-fertile female, abundant red berries, dark green smooth margined leaves.
One of my favourites I. aquifolium "ferox argentea", hedgehog holly - variegated cream / green, male with spikes all over the surface of the leaf, a bit more fussy about soil than the others, doesn't like it too heavy or wet.
Juniperus scopulurum - "skyrocket" T
A more reliable alternative the Italian cypress in the British climate and a very lovely tree in its own right. Again narrowly upright and this time with a blue-grey tinge to the foliage best brought out when planted in full sun.
Use either of these trees effectively in pairs either side of a path or entrance, or use them as punctuation marks in planting schemes.
Mahonia spp. S
Evergreen shrubs with shiny dark green holly-like leaves and large sprays of highly scented yellow flowers in the winter months. Make sure you plant it near a path or doorway otherwise you may never be tempted to venture out and appreciate the scent. M. aquifolium - Oregon grape is the toughest and will withstand quite deep shade ("Apollo" is the best variety). Others though are more delicate and less shade tolerant such as, M. x media "Charity" and M. bealei, plant one of these if conditions allow.
Phormium tenax - New Zealand Flax P
These seem to be one of the "in" plants of the moment. Great evergreen fans of sword-shaped leaves up to 10ft long in green, purple or many variegated varieties. These plants will grow large! up to 10-12ft across. Flower spikes up to 12ft tall in the "weird and striking" rather than "pretty" category.
On a different note, the Maoris of New Zealand were using these to weave all kinds of things before anyone got the idea of planting them in the garden and showing off about it. If you're quick you can claim, "I always liked them actually, they just became trendy afterwards"
The ordinary green one is the best, and Phormiums actually prefer clay soil! - zones: 8-10S/8-10W
Rhus typhina "laciniata" - Stags Horn Sumarch S
A striking shrub or small tree that earns its common name due to the shape of the branches in the winter. Handsome pinnate leaves up to 18" long that give very good autumn colors. Tends to sucker quite a lot, but a small price to pay for such a handsome plant, it also means that you get some extra plants for free to give to friends. To about 15ft tall and wide. Zones: 3-8S/3-9W
Graceful shrub to small tree, wispy frothy pink flowers produced in summer. Height and spread to 15ft. Unusual scale-like leaves produced in large numbers, likewise with the flowers, individually tiny, but loads of them.
Not a likely candidate for wet soils at first glance as it is often grown on well drained sea-side soils. I discovered its wet-tolerance when I planted it by mistake once (i.e. I wouldn't have if I'd known) in a dried out waterlogged soil in the summer. By the next spring whereas some other plants around had died, the Tamarix was doing well. Withstands a fairly high degree of wetness, but don't bother if the planting hole fills with water as you're digging it.
Bushy dense evergreen shrubs eventually to about 10ft tall and wide. Fragrant white flowers borne over a long period through winter and spring, followed by blue/black berries. Tolerates a fair amount of shade and can be hard pruned.
Vitis coignetiae - Crimson glory vine C
One of my favourite climbers this one, large bright green heavily textured leaves up to 12" across whose autumn colors earn it its common name. A vigorous and large plant that will grow to 50ft if given space in a mature tree, alternatively grow it up and over a pergola to give summer shade and fall fireworks.