Large Trees
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There’s no doubting that trees make a garden. They can be used to frame the garden or as a centrepiece: the classic visual exclamation mark. But as city gardens have become smaller and smaller, plant breeders and nurseries have turned their attention to producing smaller trees that fit them. However, as many would-be gardeners soon learn, there really is no such thing as a small tree. During my time as a nurseryman I was often faced with having to explain to a customer that there are very few 4m high trees that will fit perfectly in a tiny city garden. Nevertheless the success of plants such as Robinia pseudoacacia ‘Frisia’ and Gleditsia triacanthos ‘Sunburst’, which can now be seen in every second suburban garden, clearly shows that there is a demand for city-sized trees.
An unfortunate side-effect of this is that it can now be difficult to locate good specimen trees for larger gardens. Granted, the robinias, gleditsias and the like will eventually develop to a reasonable size, but if you have the room for large trees you are likely to want a bit more variety than is offered by the average garden centre.
There are many things that a large tree can offer that will make it worth considering. It may have variegated or otherwise unusual foliage, colourful flowers, brilliant autumn foliage, unusual bark or a different growth habit. Sometimes sheer bulk may be enough: a mature giant redwood (Sequoiadendron giganteum) doesn’t need fancy leaves and pretty flowers to make an impact. But in most cases the tree has got to offer that little something extra, otherwise you may not even be aware of its presence among all the other greenery — you literally may not be able to see the tree for the woods. As attractive as an English oak (Quercus robur) may be, it is a little too plain for most gardens, even expansive ones, and is really best suited to parks or arboretums. On the hand, the very upright form of English oak, ‘Fastigiata’, makes a great avenue tree, as it has very upright poplar-like growth when young and broadens slightly in later life.
Many of the larger trees are deciduous and autumn colour is a common feature. Trees like the red oaks (Q. coccinea and Q. rubra), pin oak (Q. palustris), liquidamabar (Liquidambar styraciflua), ginkgo (Ginkgo biloba) and the ashes (Fraxinus spp.) are widely planted and make a tremendous display where the climate suits them.
Summer-coloured foliage forms are also widely grown. Most gardeners will have marvelled at the blackish-purple leaves of the copper beech (Fagus sylvatica ‘Atropunicea’ [‘Riversii’]), and the purple birch (Betula pendula ‘Purpurea,). The golden elm (Ulmus procera ‘Louis van Houtte’) and the purple box elder (Acer negundo ‘Violaceum’) are also very attractive and have unusual flowers in spring.
Less common among large trees is variegated foliage. Fortunately my all time favourite, the variegated Norway maple (A. platanoides ‘Drummondii’), is among the more readily available. This tree has it all — size, form and colour. It develops into an 18m high tree with a rounded head and a sturdy trunk; its foliage, which is the typical maple-leaf shape, is light green with a broad yellowish to silvery-white edge. ‘Drummondii’ is magnificent at any time but looks particularly attractive against a deep blue sky. Other impressive specimens include the variegated tulip tree (Liriodendron tulipifera ‘Aureo-marginatum’), variegated elm (U. carpinifolia ‘Variegata’) and silver box elder (A. negundo ‘Argenteo Variegatum’). Acer platanoides ‘Waldesii’ is a striking tree with silvery flecked leaves, but I’ve only ever seen one specimen and that is in the Christchurch Botanic Gardens.
Unusually shaped leaves can also be an appealing feature. Three trees that immediately come to mind are the tulip tree, cutleaf weeping birch (B. pendula ‘Dalecarlica’) and cutleaf alder (Alnus glutinosa ‘Laciniata’) The birch and the alder are specially selected forms with finely dissected leaves that are very attractive. However, think twice before planting these trees as they are very ground-robbing.
Flowers can add to the appeal of a large tree but they are often so high up that they can’t be seen and few large, hardy deciduous trees have much in the way of an impressive flower display. Indian bean (Catalpa bignonioides), Paulownia tomentosa and the very unusual white-flowered dove or handkerchief tree (Davidia involucrata) are worth considering in cold areas. But it is among the more tender trees that the best flowering specimens are found: Illawarra flame tree (Brachychiton acerifolia), firewheel tree (Stenocarpus sinuata) and silky oak (Grevillea robusta) are all renowned for their striking flowers. The common scarlet-flowering gum (Eucalyptus ficifolia) and purple-flowered jacaranda (Jacaranda mimosifolia) will also grow large enough to dominate a garden, and besides, with the riot of colour that they produce it’s hard to ignore them.
Many large trees have a considerable expanse of bare trunk before the foliage canopy starts, so unusual bark patterns and textures can really stand out. This is an area where many of the eucalypts have great appeal; the most striking is probably the ghost gum (E. pauciflora), the bark of which peels to reveal a stark white trunk that creates a dramatic effect against a backdrop of blue or leaden-grey sky. The peeling bark and silvery-white trunk of the common silver birch (B. pendula) is not to be ignored either. Consider too, the camphor tree (Cinnamomum camphora), paperbark maple (A. griseum) and the scale-like bark of the maritime pine (Pinus pinaster syn. maritima).
Most large conifers tend to be rather dull-coloured and a bit too over-bearing, but the Japanese cedar (Cryptomeria japonica), which changes colour with the seasons; the non-conifer-like ginkgo; and our native rimu (Dacrydium cupressinum), with its bronze foliage and graceful weeping habit, are distinctive enough to stand out in any company. The deciduous conifers, such as swamp cypress (Taxodium distichum) and dawn redwood (Metasequoia glyptostroboides) add a touch of drama in the autumn with their russet-red tones. Also, their spring foliage is a unique and refreshing shade of bright green. Swamp cypress has the added benefit of growing where few other trees will — in up to 50 cm of water.
Among the natives a few stand out as being superb specimens. Titoki (Alectryon excelsus), karaka (Corynocarpus laevigata) and taraire (Beilschmiedia tarairi) have attractive glossy leaves and unusual fruit, and of course the large kowhai (Sophora tetraptera) must be one of the first choices for any collection of flowering trees, as should the bottlebrush-like white-flowered kamahi (Weinmannia racemosa). The variegated forms of Hoheria populnea will develop into impressive trees with age and flower well too.
Don’t forget, large doesn’t only mean tall; width is also important. Few gardens have the room for plants like the Camperdown elm (Ulmus glabra ‘Camperdownii’) with its spread of 15m or so, but where they can be grown they form an immediate focal point.
Palms too, add interest because of their very distinctive form, which often adds height with very little width, and because of the tropical effect they create. Canary Island date palm (Phoenix canariensis) and the Washingtonia palms are the ones normally used when large landscape-dominating plants are required but you could also consider the Chilean wine palm (Jubaea chilensis). Where the climate allows, Archontophoenix cunninghamiana, the Livistona palms, ‘Queen Palm’ (Syagrus romanzoffiana formerly Arecastrum romanzoffiana) and Rhopalostylis baueri are all capable of dominating a landscape. The native nikau (Rhopalostylis sapida) is probably too small to be considered a large tree.
How you use trees can be just as important as which you choose. Most of trees mentioned here are so spectacular or different and distinctive that they really must be used as specimens — planted out on their own where they can be seen. To hide them among other trees would be a waste and to mix them together is just asking for jarring clashes and a jumbled look. Just one of these trees can lift a garden out of the ordinary; and if I had to have just one it would be the variegated Norway maple.
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As mentioned in the article, garden centres don’t sell many large trees these days and you may have difficulty finding some of those listed. Ringing around the nurseries and garden centres will locate quite a few of them but often you will have to buy by mail order.
Copyright Geoff Bryant
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