Download Subtropicals for NZ Designers 2015

Subtropicals for Designers in Northern NZ
NZ is not tropical and the idea that we have subtropical districts is pushing the
definition a bit. BUT we can grow some wonderful subtropical plants in wellsheltered, warm microclimates in this country. A surprising number of subtropical
plants are actually tolerant of light frosts once well-established.
The crucial difference between our climate in the North here and that of most of the
subtropics is not the temperature range, its the fact that winter is wet which makes our
winter soils MUCH colder than if they were dry and it also drives air from the soil
when it is most needed by subtropical plants.
Loose friable soil with free drainage, good wind-shelter, steady summer moisture and
bright dappled light are what is needed to succeed with most of the subtropical
beauties I will discuss today.
1. Dramatic textural contrasts in a front door planting using the Alpinia ginger
(A. malaccensis hybrid) ‘Pink Perfection’ in pottery bowl. Medinilla
myriantha in ground in dappled light beneath a portico with little moisture.
2. A steep South facing bank planted with contrasting foliage textures
including a small clumping bamboo, Colocasia illustris ‘Blue Nile’, a bright
orange Sinningia hybrid, Neoregelias and begonias, forms the backdrop to a
deck at an Auckland gardener’s front door.
3. Strobilanthes gossypinus with Dichondra ‘Silver Falls’ provides dramatic
contrast with green Coprosma repens ‘Poor Knights’, Coprosma acerosa
‘Hawera’, Alpinia zerumbet, Cycas revoluta and red-leaved flax.
4. Philodendron hybrid climbs a palm trunk beside a lush clump of Cordyline
stricta.
5. Philodendron erubescens is an enthusiastic, heavy climber on a swamp
paperbark, Melaleuca leucadendra.
6. Philodendron renauxii is a mainly terrestrial scrambler with leathery ovate
leaves and short internodes which makes it a beautiful groundcover in
dappled light to full shade.
7. Philodendron xanadu is (despite the claims it is a cultivar of P.
bipinnatifidum) a wild species which needs warm roots to thrive here. This
street planting in Whangarei shows it doing very well with 80cm leaves in a
raised stone planter in full sun.
8. Alocasia gageana is a Malaysian species, very robust, forming lush clumps
quickly without spreading much. Usually does not seed in NZ and its
hardiness keeps it looking good all year unless frosted.
9. Xanthosoma sagittifolia is a giant taro from South America where it has
been grown for food for millennia. Its known widely as ‘Malanga’,
‘Cocoyam’ or ‘Yautia’ among other local names. It makes a spectacular
garden specimen in semi-shade with no wind.
10. Xanthosoma violacea or ‘Blue Tannia’, ‘Blue Yautia’ or ‘Violet Taro’
grows about 1m high. Very important edible crop in West Indies. Full sun or
dappled shade.
11. Alocasia ‘Portadora’ is a sterile hybrid that grows to 2.5m high and is a
very strong, wind-hardy taro. Striking form. Does not produce pups or seed.
12. Tropical figs. Banyan trees. Ficus benghalensis, the classic Indian fig with
many trunks developed from roots coming down from the branches. Slow
growth in NZ but quite hardy where frosts are light.
Ficus religiosa is the fabled Indian Bodhi tree or Peepal tree, sacred to
Buddhists and Hindus and a very beautiful tree by any standard. Slow growth
and frost-tender initially but becomes an elegant weeping specimen tree
eventually.
13. Ficus prolixa is a stately huge tree in Samoa, Tonga & Fiji where it towers
far above the forest with no true trunk, just a maze of prop-like roots which
start from high up where the much thicker branches form a broad canopy.
This grows here (just) but needs a very warm spot to get started.
14. Ficus macrophylla subsp columnaris is a huge stately tree from Lord Howe
Island. The tree in this pic is the source of the seed I grew my own
specimens from. They grow very fast in NZ and start making copious aerial
roots within about 3 years. Gibbs Sculpture Farm has taken about 25 of
these to plant in the landscape among the sculptures as they are tolerant of
the fierce winds that thrash that property. Not for an urban environment.
15. Caesalpinia ferrea, the leopard tree from Brazil thrives in our climate and
will cope with quite heavy frost once established. An elegant species used
as a street tree in subtropical cities. Briefly deciduous in Spring. Its yellow
flowers are pretty in summer but the silky smooth, patterned bark is the
main event. Grows to about 4m - 5m in NZ but can reach 30m in the tropics.
16. Australian swamp paperbark: Melaleuca quinquenervia is found in Southern
Australia around and in swamps and rivers. It also grows well here in
similar conditions. Despite the fact that it is frowned on by the regional
councils of Auckland and Northland, it does not produce seedlings under
natural conditions here. It is a very sculptural small tree here to about 5m
and it makes a fast-growing nectar-rich tree for boggy conditions and can be
very useful to help prevent erosion around waterways. Grows equally well
in dry soils too.
17. Melaleuca leucadendra is a more tropical species with elegant weeping
form and not so tolerant to boggy soil, preferring light sandy/volcanic soils.
18. Melaleuca viridiflora is yet another paperbark with very similar form and
green flowers. I am propagating a burgundy-flowered form which is found
naturally along the Queensland coast North of Cairns.
19. The beach hibiscus, Hibiscus tiliaceus, is found naturalised throughout the
tropics on beaches and coastlines.
20. The beach hibiscus is a small tree to about 4m in NZ which blooms all
summer and autumn with flowers which change colour over several days
from lemon yellow to orange-red. Hardy and easy to manage as a garden
tree or shrub.
21. Syzygium luehmanii, the riberry, from Eastern Australian rainforest is a
small tree to 4 or 5m with spectacular pink young foliage. Growth flushes
continue throughout the year. Seldom produces flowers or seeds in NZ.
Shade and sun tolerant.
22. Syzygium wilsonii needs shade to avoid foliage scorching.
23. It is a scrambling tropical shrub with spectacular large, terminal, burgundy
inflorescenses through summer. Staked to grow upright for a metre or two it
will cascade from that point or down a wall.
24. Bauhinia variegata is a small tree to about 4m at maturity, producing a
massed flower display during Spring over several months, defoliating as the
flowers develop. The colour varies from white to pink and red. The latin
name refers to the variegated flowers not the leaves.
25. There are a range of colours available from red to white.
26. Bauhinia galpinii is a South African sprawling shrub with bright orange
flowers through Autumn. It is winter deciduous and very hardy in welldrained soil.
27. Tecoma stans, from Central & South America, is a shrub or tree which
grows 4m - 6m and flowers almost continuously throughout the year with
strongly perfumed golden-yellow trumpet flowers typical of the Bignonia
family. Frost-tender when young but hardy with age.
28. Brugmansias originate in South America and have been widely hybridised
to create many handsome cultivars, single and double flowered in a range of
colours through every shade of pink, cream, yellow and orange.
29. Most but not all are night perfumed to attract night-flying pollinators. The
red and yellow species B. sanguinea with small tubular flowers is from high
altitude and finds our climate too hot in summer which results in defoliation
from November to March unless it is grown in cool, shady conditions.
30. Some pink cultivars and their pink ancestor, the species B. versicolor
‘Ecuador Pink’, are sun-sensitive resulting in flowers collapsing very
quickly in sunny conditions.
31. They are all frost-sensitive but re-grow rapidly as weather warms up in
Spring.
32. Pandanus furcatus is a large cool climate pandanus from the Himalayan
foothills and montane subtropics throughout Asia and in Australia. The large
fruits are sweet and edible.
33. Alpinia gingers, known collectively as ‘shell ginger’ originate in South and
East Asia with one species in Australia.
34. Most are comfortable in warmer parts of NZ and all prefer bright dappled
light to look their best.
35. Flowering occurs through summer on the previous summer’s growth.
36. There are a range of species
37. and many new hybrids available in NZ. The Thai spice ‘galangal’ (‘Kha’ in
Thailand) is very tropical and difficult to grow outdoors but is a very
worthwhile culinary plant to grow in a pot and bring indoors over winter.
38. The species and hybrids of the genus Hedychium are known as ‘butterfly
gingers’ in the West and include the dreaded ‘Kahili ginger’ which is such a
weed in this country.
39. However most other members of the genus are reasonably easy to manage.
Their growth habit is fairly aggressive so they need to be contained in some
way to avoid annual removal of excess rhizomes but most of the hybrids
produce few if any seed. Most are perfumed and the glamorous flowers now
include a couple of pink forms and some rich orange and yellow hybrids.
Flowering occurs from February to May.
40. The Kaempferia gingers are deciduous, emerging in Spring and dying off in
winter. K. rotunda is shade and sun tolerant and makes a handsome 40cm
clump of foliage for 7 to 8 months of the year.
41. The sparkling Spring flowers emerge from the soil before the leaves.
42. Kaempferia pulchra reaches only 15cm in height and prefers shade but the
mauve-pink flowers continue throughout the growing season. These also
make beautiful houseplants.
43. Curcuma zedoaria is known as zedoary and also as ‘mango ginger’. It is
also called ‘white turmeric’ as it is closely related to turmeric. It is a
handsome deciduous plant with 50cm - 80cm tall foliage for 8 months of the
year. The striking red flower spikes emerge in December soon after the
leaves. It is used as athickening agent, a spice and medicinally throughout
India and SE Asia.
44. The genus Costus, the spiral gingers, is tropical but some species are more
hardy than others. Costus barbatus is known as ‘Tower Ginger’ and is
arguably the most spectacular of them. It requires bright shade and perfect
wind-shelter without frost. The flower spikes continue developing over 12
months so the plant has dramatic flower colour all year.
45. Costus speciosus is the hardiest of this genus, and will grow almost
anywhere in NZ in bright dappled light. This one is deciduous and the
shoots that emerge from the soil in Spring will reach a metre in height with
flowers though the Autumn.
46. Costus pictus is a useful garden plant in Auckland and North in bright shade
with good shelter from wind. The cane-like stems which reach 1m and the
lettuce-green leaves are very handsome. The flowers occur all year as a
cone-like terminal inflorescence on the leafy stems and on separate leafless
flowering stems. This is the so-called ‘insulin plant’ used to control blood
sugar levels in India. It is native to Mexico.
47. Crinum asiaticum is a complex group of subspecies of Asian-Pacific lilies
many of which thrive here in full sun or shade, bog or dry soil.
48. Most reach a metre or more in height with big spidery white flowers through
summer.
49. Cordyline petiolaris from North-eastern Australia is a large Cordyline with
long paddle shaped leaves and red berries which thrives in NZ, forming
clumps up to 4m high.
50. Cordyline fruticosa originates in Papua New Guinea and has been taken
throughout the Pacific by the first people to settle there, even to NZ by early
Maori. It was the main source of dietary sugar until sugar cane arrived with
European colonists.
51. The very colourful cultivars need good drainage, shelter and dappled light to
look their best. Some varieties thrive here and look good all year long but
the vivid pink types are too tender for most gardens and spend half the year
looking very tatty. Snail damage is the other big problem but a couple of
mesurol pellets lodged in the centre of each rosette fixes that for several
months.
52. Calliandra haematocephala is another Central American shrub which does
well in almost frost-free conditions in full sun.
53. These flower for at least 8 months of each year and the vivid colour is a
delight, especially as the nectar feeding birds come to it daily.
54. Quite a number of Heliconias grow and flower well here in warm dappled
light with maximum shelter. They are heavy feeders like all the
banana/strelitzia/ginger group and need steady moisture throughout the
summer. H. schiedeana flowers emerge in November and last all year. It is
an outstanding garden plant around 2m to 2.4m high with a compact growth
habit unlike H. subulata which spreads alarmingly fast if not confined. H.
spissa has attractive shaggy leaves and rather muted pink flowers and
reaches about 1.5 – 1.8m.
55. Heliconia tortuosa is the latest species to be imported and is an outstanding
success with dramatic fiery red large upright heads for 4 months from
February. It is compact and reaches only 1.5m in height. And H.
bourgaeana is a very tall one which needs very calm conditions and rich soil
to flower. The very large fluorescent pink flowers are amazing but it is fairly
marginal in NZ.
56. Mussaenda frondosa, from South and East Asia is called the ‘white butterfly
bush’ by Western gardeners because the white bracts which accompany the
little orange flowers look like and attract a mass of butterflies. The bracts
last for about 8 months, sometimes longer in milder years. This is best
grown in full sun and given a good prune back every couple of years.
57. Lomandra hystrix is a giant Australian grass-like plant found in both boggy
and dry environments and is even salt tolerant enough to handle brackish
estuarine tides. It is remarkably tough and can be used to help control
erosion on dam and creek margins. Its glossy foliage can reach 1.5m high. It
always looks its best in dappled light and is one of the few plants that will
thrive under old totara trees along with clivia.
58. Canistropsis billbergioides is a very useful understorey plant for year round
colour in deep shade. The rich orange and yellow flower heads last for about
14 months.
59. We in the warmest parts of NZ are in the privileged position of being able to
grow an amazingly broad range of plants and we have the opportunity to
create our own individual, boundary-breaking landscape styles.
A little risk-taking has the potential to launch us into new landscape design
territory.
Russell Fransham Subtropicals
Website www.subtropical.co.nz with comprehensive
catalogue.