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Of the 77 species of banksia, the majority grow in southwest Western
Australia - and (as many a gardener will be able to painfully recall)
the majority of these cannot cope with Sydney's weather. The reason for
this is that summer humidity provides ideal conditions for the spread
of the rootrot fungus Phytophthora cinnamomi, to which western
banksias are exquisitely sensitive. Some species, such as Banksia speciosa
may appear to grow quickly and thrive for a couple of years before succumbing
rapidly one summer.
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Banksias are used to well-drained sandy soils or sandy loams and sunny
positions. Heavy or clay soils pose some problems. The only species which
copes well with heavy soils is Banksia integrifolia, though Banksia
robur is fine with poor drainage. Some forms of Banksia spinulosa
are found naturally on clay soils in the Sydney basin but growth can
be slow. Alternately, soils may be 'improved' by adding gypsum
or other soil conditioner or by raising the growing level by at least
30-60 cm. Banksias appreciate extra water during dry periods, especially
during summer. Special care shold be taken not to let them dry out
until established (i.e. they get roots deep into the gorund and find the
water table, which may take anything up to 2 years). Fertilizing with
phosphorus should be minimal. A slow release low phosphorous treatment
is best. If new leaves turn yellow use iron chelate or iron suphate according
to the instructions. Species which are lignotuberous, such as Banksia
robur, B. spinulosa and B. serrata, may
be pruned -even back to ground level! Others, such as B. ericifolia
and B. "Giant Candles" are nonlignotuberous and should be pruned
lightly (not below green foliage) and often.
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In the past, banksias in nurseries were usually grown from seed or from
cuttings from plants raised from seed from the wild. These days more and
more named and registered varieties from recognised companies such as
Austraflora or Merricks are seen in nurseries - these are all cutting-propagated.
This means that the plant grown will be predictable in habit and flower
colour. Some seed from dwarf plants may not remain so. Local volunteer
or community nurseries are the best source if you are
looking for banksia populations that come from your local area
(known as 'local provenance' or indigenous plants)- many eastern species
are widespread, so you or the nurseryman may have no idea whether the
nice Banksia spinulosa you're looking at comes from North Queensland,
NSW or Victoria!
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Some of the most showy Banksias are those from WA which are very difficult
to grow in the Sydney region, generally succumbing within a couple of
years of planting (and well before they've had time to flower!).
Some species may be available, grafted on to fungal-resistant eastern
species. Combinations to look out for include Banksia brownii
on B. integrifolia and B. speciosa on B. aemula.
If you want to grow Banksias, and every garden should have them, start
with EASTERN SPECIES. As your knowledge and experience grows, you can-then
experiment with other more difficult types.
Banksia integrifolia is the easiest banksia to grow and the
most forgiving in regards to soil (it will grow in most soils and tolerates
alkalinity too). It is a fast growing plant of open, rangy habit and can
grow into a large tree. Some unnamed dwarf forms are in nurseries, though
some reports indicate they do grow larger than predicted! The prostrate
form, "Austraflora Roller Coaster" does remain prostrate. Leaves
are serated on young plants, entire on older. The pale yellow to yellow
flowers occur in autumn, some forms are greenish in bud, others yellow. In
Sydney, the local form is variety integrifolia, which is also
the form most commonly seen in nurseries. There is a mountain subspecies
monticola with narrow leaves, though this is not seen in nurseries
yet.
Banksia serrata occurs in near coastal regions from Queensland
to Tasmania. 10 to 12 m high. Large flower spikes summer-autumn, grey-green
in bud, turning yellow. Large woody cones outstanding. slow growing but
long lived. It has attractive foliage and develops a gnarled warty grey
trunk over time, however may take several years to flower. Especially
good for exposed coastal sites and as a sand binder. A prostrate form
known as B. "Austraflora Pygmy Possum" is available. Banksia
aemula is similar but leaves are smaller and flowers brighter. Its
fruit is the "Big Bad Banksia Man" of May Gibbs' stories. Both are fairly
finicky in their soil requirements, preferring a sandy well drained sunny
site.
The Swamp Banksia (B. robur) grows in sand or peaty sand in
Qld and NSW. It is a spreading shrub to 2.5 metres. It has very large,
leathery leaves with serrated margins up to 30cm long. New growth is colourful,
wih shades red, maroon or brown with a dense felt-like covering of brown
hairs. Stunning large flower spikes, metallic green with pinkish styles
in bud, becoming cream-yellow and fading to brown. This one likes plenty
of moisture.
Banksia oblongifolia used to be known as B. asplenifolia
and grows from Qld to Ulladulla, NSW, mostly near the coast
on moist sites. A 1 to 3m spreading shrub. Very attractive (but slow
growing) garden shrub with velvety red or brown new growth
on foliage. In bud, flowers can have mauve or aqua highlights before opening
to a dull yellow. Best in moist soil in sun or partial shade. B. paludosa
is related. From central NSW in coast and mountains. This is a compact
shrub to 1m x 1.5m. It does best in sunny position. Both can be pruned
to shape.
The Hinchinbrook or Blue Banksia (Banksia plagiocarpa) from
North Queensland grows readily in Sydney and is frost tolerant. It is
related to B. oblongifolia and has more vivid furry red new growth.
The other outstanding feature are the spikes, which are generally
blue-grey in bud. It grows to 4m or so and prefers sandy soils. Hinchinbrook
gets a lot of rain so this plant would appreciate extra moisture.
B. ericifolia is found in the Sydney Basin and Blue Mountains on
sandstone soils. A strong growing bushy shrub with long red to orange
spikes with red styles. Some forms, such as 'Kanangra Gold' have paler
orange spikes with gold styles. It flowers in late autumn and
winter and is very attractive to birds. Plant in sandy soils and
don't prune hard.
The Hairpin Banksia (B. spinulosa) is a showy shrub
1-3 m by 1-2m, with long, narrow leaves. Flowers over a long period through
autumn and early winter with spikes from yellow to orange, and styles
of yellow, orange, red, pink, maroon or black colour. The subspecies most
commonly seen in nurseries is variety collina (Hill Banksia),
which naturally occurs north of the Hawkesbury whereas variety spinulosa
occurs to the south. Given that the varieties hybridise, try and get a
local provenance form from your local community nursery, Bushcare or Australian
Plants Society group. There are, however, some marvellous dwarf forms
available for the city gardener - 'Stumpy Gold' is a form of variety
collina originally from the Central Coast, while "Birthday
Candles", 'Coastal Cushion' and 'Golden Cascade' are forms of variety
spinulosa from the south coast of NSW. In general, Hairpin Banksias
prefer sandy well-drained soils, though some local forms hailing from
Wiannamatta Shales may do OK on heavier soils.
Banksia "Giant Candles" is an excellent garden plant - believed
to be a hybrid between B. ericifolia and B. spinulosa.
It grows to 5m high and wide with tall (30cm) all-orange spikes in autumn.
Best in well-drained soils and sunny aspects.
Finally, of the Western species, the most successful
are the two more vigorous prostrate species - Banksia blechnifolia
and B. petiolaris. Both have been grown by many gardeners in
well-drained sandy beds. Banksia blechnifolia in particular appreciates
some extra moisture and will reward you with odd orangey pinkish spikes
in late spring. Banksia media is the other species which has
been grown with some success.
- Cas Liber
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