Trees for small gardens (or small trees for gardens)
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Although it wasn’t a conscious decision, The use of trees in the garden has been a recurring theme in
my articles. Previously I’ve covered large specimen trees, flowering trees,
conifers and palms. This month I’m going to look at the smaller trees, which,
of course, are not only suitable for small gardens, but also for small sections
of large gardens or places such as patios or entrances where a small tree is
appropriate.
What is a small tree? Well, that’s a
question fraught with problems. It’s not just the question of when a shrub
becomes a tree, there’s also the difficulty of defining the difference between
small and large. For the purposes of this article I’m defining a tree as a
single trunked plant over 2 m tall, so something like a magnolia can be a
shrub or a tree depending on its form or how it’s trained. As regards size, I
think it’s more a matter of manageability than defining an absolute size: a
small tree is one that is naturally compact or easily controlled, say a maximum
height of around 6–7 m.
Beyond basic trimming and
thinning try to avoid pruning. It’s infinitely
preferable to choose a tree that fits the site properly rather than have to
hack a larger tree back to the right size. Not only does such practice spoil
the shape of the tree, it may also weaken it and leave it susceptible to
disease.
In a small garden spread is often a more
significant consideration than height. Fortunately it’s not a difficult to
control as height; just thinning out and tipping the branches will often solve
the problem without the need to resort to major surgery. The key is the early
recognition of any potential problems. Training and shaping a young tree is far
less work than trying to manage an overgrown adult specimen.
Small trees in the landscape
When space is limited how you use it is of
paramount importance. In a small garden, especially one bordered with fences or
hedges, trees can greatly alter or even define the microclimate within. The
shade and shelter they provide greatly influences the choice of companion
plants and the general feel of the garden.
The worry that most gardeners have is that
by planting trees in a confined space they will end up with a dark, cold
garden. There’s also the concern that trees may interfere with underground
pipes and overhead wires or guttering. I think in most cases the potential for
roots to invades pipes and branches to cause
structural damage is overstated, but the effect of shading on the brightness
and warmth of a garden is a very important consideration.
Three things mainly determine the degree of
shade and shelter a tree provides: the aspect, foliage density and whether the
tree is evergreen or deciduous.
Aspect
Positioning determines where a trees’ shade
is cast. It seems such an obvious thing to say but it’s often overlooked. In a
large garden a misplaced tree is not likely to be much of a problem. It just
creates another area for shade-loving plants. In a small garden, however, it
can be a disaster. Large parts of the garden may be cast in a permanent pall of
deep shade that not only makes the garden cold and unwelcoming, it limits the
range of underplanting material to those plants that tolerate such conditions.
The solution is simple: commonsense and
forethought. Consider the changing position of the sun though the day and over
the seasons and plan the positioning of the trees to provided
shade where and when it is needed rather than where it is least desirable.
Position the trees where they won’t shade out smaller sun-loving plants and
stagger the heights of your plantings so they all receive adequate light.
Consider too, whether you actually need
trees. Is the garden large enough for trees? Will large shrubs do the same job?
Can you capitalise on the trees in your neighbours’ gardens or in neighbouring
parts of your own garden? A tree hanging over the fence may be just as useful
and effective as one planted on your soil.
Foliage
Large, heavy leathery leaves block out far
more light that light ferny foliage. While they also provide more protection
form winter frosts and driving rain, they cast too much shade to be well suited
to a very small garden. Also, large leaves can take a long time to break down
when they fall. A dense layer of large fallen leaves can completely smother
small shrubs and perennials. If space is really limited, pinnate foliage like
that of Albizia, Gleditsia and Sophora is usually preferable. Even if
quite dense it allows light through and any fallen leaves break down quickly.
Evergreen or deciduous?
Given the choice, most gardeners opt for
evergreen over deciduous. The usual comment is “I don’t want my garden to look
dead in winter.” If only it were that straightforward. Although ultimately it’s
a matter of personal preference, the decision should more wisely be based on
the size of the garden, its aspect and the foliage type of the trees in
question.
It may be acceptable for a small garden to
be shaded by evergreens in summer, but come winter that same cooling shade
makes the garden cold and damp. Using deciduous trees is an obvious answer: the
foliage is there when shade is needed and gone when the sun is most welcome.
Again, leaf size is important. It may be
possible to get away with using a large-leaved magnolia if it is deciduous, but
an evergreen with similar foliage would cast dense shade throughout the year
making it almost impossible to grow anything under the tree.
Design
Having decided on the general positioning
and style of tree, it’s time to consider the more aesthetic aspects.
Do you want a garden with a theme and how
will that influence your tree selection? A garden with a desert or dry country
theme would suit a tree-sized succulent such as Aloe bainseii; Pencil cypresses (Cupressus sempervirens) would suit a Mediterranean garden; a
graceful Styrax is an ideal shade
tree for rhododendrons; and a native gardens needs
native trees.
What about flowers, fragrance or attracting
birds into the garden? Well, rather than take a lot of space covering these
things in detail I’ll simply say that the range of trees is wide enough to
accommodate all of them. If flowers are important there are flowering trees, if
scent is required there are small trees with aromatic foliage and fragrant
flowers, and there are plenty of trees with fruit and nectar to attract birds.
And of course, trees are attractive nesting sites even without additional
enticements.
Foliage colour is very important. If the
garden has but one tree, something very strongly coloured, such as a silver
pear (Pyrus salicifolia ‘Pendula’),
can dictate the style and colour scheme of the entire garden. Less
distinctively coloured foliage blends more easily and allows the tree to
perform its functional tasks without the risk of constantly intruding on the
garden design.
Where it’s possible to fit say three to
five trees, a garden often has a greater sense of unity if the choice is
limited to just one or two varieties. That may seem boring, but remember trees
are often at their best when they are operating in the background, acting as a
framework for the garden and the more flamboyant plants it may contain.
The trees
In addition to the few already mentioned
there are hundreds of small trees and large shrubs that can be trained as
trees. An article this size can only hope to cover the tip of the iceberg but
here are some to consider.
New Zealand Natives
The most instantly recognisable native tree must be the cabbage tree (Cordyline australis). It’s a superb all-rounder with interesting foliage, attractive scented flowers and unusual white fruit. Both the flowers and fruit are attractive to birds. The broad-leaved cabbage tree (Cordyline indivisa) has the added benefit of lush, deeply ribbed blue-green foliage but is not as easy to cultivate, preferring rich soil, a moist climate and shelter from strong wind.
The two tree-sized kowhai species (Sophora microphylla and S. tetraptera) are similar to one another. Sophora tetraptera has foliage with large leaflets as well as larger and brighter flowers. It’s probably more effective as a specimen plant, while S. microphylla is better planted in groups. The flowers are full of nectar and popular with most native birds, especially tuis.
The small lancewoods (Pseudopanax crassifolius and P.
ferox) have very stiffly erect and distinctive juvenile forms but both
eventually develop into round-headed trees with very deep green foliage. The
juvenile leaves are long and narrow with toothed edges, particularly vicious on
P. ferox.
Although the ratas and the pohutukawa are
too large to be called small trees, their relative from the Kermadec Islands, Metrosideros kermadecensis, is far more
compact and just as colourful. A shrub for many years, it will eventually
develop into a tree around 6–8m tall. The variegated foliage form is smaller.
For a lush tropical foliage effect its would be hard to beat the puka (Meryta sinclairii). It’s suitable as a container plant as well as
for the open garden. However, its frost tenderness limits its range. In cold
winter areas the five finger or whauwhaupaku (Pseudopanax arboreus) is similarly lush
with the added benefit of far greater frost tolerance.
Don’t forget the tree ferns. They are very graceful and quite different from what we normally expect a tree to be. The same is true for the nikau palm (Rhopalostylis sapida).
Other large shrubs or small trees native to
New Zealand include makamaka (Ackama
roseafolia), wharangi (Melicope
ternata), pate (Schefflera digitata),
mahoe or whiteywood (Melicytus ramiflorus),
karaka (Corynocarpus laevigatus) and
many of the Pittosporum and Olearia species.
Exotics
One can’t talk about exotic small trees
without mentioning those most commonly seen: the Japanese maples (Acer palmatum and A. japonicum cultivars), the flowering cherries, plums and apricots
(Prunus spp. and cvs.), crabapples (Malus spp. and cvs.) and the smaller
magnolias. As they’re so well known I’m not going to describe particular
plants. Suffice it to say that they’re all extremely beautiful but you should
be very careful when selecting. It’s all too easy to choose a pretty-foliaged
or -flowered plant only to find that it eventually grows too large.
Without doubt my favourite small trees are
the dogwoods. Many demand a continental climate with clearly defined seasons
and find New Zealand’s maritime climate not entirely to their liking. The Himalayan
strawberry tree (Cornus capitata) is
generally reliable and prefers mild winters. It has cream flower bracts and red
warty fruit. Cornus kousa, which has
small white bracts, also does well, but my two favourites, Cornus florida (particularly the form ‘Cherokee
Chief’) and Cornus nuttallii, are a
little temperamental. The popular ‘Eddies White Wonder’ is a hybrid between
these two species.
For most of the year the Japanese snowdrop
tree (Styrax japonica) is rather
unprepossessing, a plain green tree with simple deciduous foliage. However,
when in flower it is a plant of unrivalled grace: beautiful sprays of white
blooms against a dark green background. Styrax
obassia has similar flowers but rather coarser foliage.
The epaulette tree (Pterostyrax hispida) creates a similar effect, though its flowers
are in hanging chains rather than slightly pendulous horizontal sprays. The
common name is derived from the supposed resemblance of the panicles to the
braid on the epaulettes of formal military uniforms.
Fraxinus
sieboldiana (syn F. mariesii) is a small ash tree with plumes of small creamy white
flowers. The blooms have a rather spicy fragrance. A slender tree that doesn’t
demand much space, it’s at its best in late spring to early summer.
Shad bush (Amelanchier lamarckii [often-mislabelled A. canadensis, a far less common species]) is an erect deciduous
tree that in spring bears drooping racemes of white flowers. Its rich
orange-red autumn foliage is an added attraction. It needs cool winter
conditions to flower reliably.
The various Cercis species are of a similar size and habit. They too are
deciduous and generally prefer cool winter conditions. The purple-pink-flowered
Judas tree (Cercis siliquastrum) is
the most common, though I favour Cercis
canadensis ‘Forest Pansy’, which has lovely purple foliage throughout the
growing and develops glowing orange and yellow coloration in autumn. Its
flowers are soft pink and typically pea-like.
The banksias are unusual small trees.
Although they are sometimes rather sparse and open, their flower cones are
attractive and certainly distinctive. I think I prefer the waratah (Telopea speciosissima) though because of
its neater habit and lusher foliage. In mild climates another Australian protea
family plant, the Queensland firewheel tree (Stenocarpus
sinuatus), can be relied on to produce masses of red and gold flowers in
early winter.
Ceratopetalum
gummiferum, Grevillea
banksii and Eucryphia moorei are
a few of the other Australian species worth considering. The Chilean eucryphias
and the hybrids between Chilean and Australian species are some of the most
attractive yet often overlooked summer-flowering trees. Their white, single,
camellia-like blooms contrast well with their dark green leaves and are often
slightly scented.
Having praised our native Sophora species, I shouldn’t ignore the
pagoda tree (Sophora japonica).
Unlike the natives, which drop their leaves on flowering, this Japanese species
is winter deciduous in the normal manner. In spring it bears magnificent
panicles of cream blooms. It is often sold as a grafted weeping standard on 2m
stock, and while such plants are expensive, the effect they create is well
worth the cost.
Gardeners in cool climates are very familiar with the common rowan (Sorbus aucuparia). It is a small tree with late spring sprays of rather unpleasantly scented creamy white flowers followed by magnificent clusters of orange-red berries. While it’s a very attractive and adaptable tree, for something a little different try S. hupehensis (pink-tinted white berries), S. cashmeriana (pure white berries) or S. aria (orange-red berries with deep green, slightly felted foliage).
The many forms of the honey locust (Gleditsia triacanthos) offer a wide range of foliage types, colours and tree sizes. The yellow-leaved ‘Sunburst’ and the purple-red ‘Ruby Lace’ are probably the best known. Robinia ‘Mop Top’ and ‘Lace Lady’ offer similar growth habits.
That’s just a small selection. Any self-respecting nursery should be able to provide most of them and a few more besides. Choice therefore is not likely to be problem, it’s more a matter of making up your mind.
Copyright Geoff Bryant
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