Between 1969 and 1976, seedlings of 102 eucalyptus species were planted in a
coastal garden at Baily,
(53.4 N latitude) to test their hardiness and suitability as ornamental trees.
Although many species were killed by low temperatures, including all those
from from Western Australia, Queensland and South Australia, plants of 37
species from New South Wales, Victoria and Tasmania are still alive and growing
well in 1992, 16 to 23 years after planting.
The results suggests that a range of species, in addition to E. gunnii
and others normally recommended, could be planted in mild areas in Ireland for
garden decoration. Among those which survived temperatures down to -6 C and are
suitable for this purpose are:- E. acaciaeformis (small, green, sessile
juvenile foliage), E. cinerea (blue green ovate, sessile foliage), E.
kitsoniana (bright green foliage and floriferous) and E. linearis
(graceful habit, linear green leaves).
has only about 1,400 species of flowering plants and ferns compared with
approximately 2,500 species in Britain. However, the
temperate climate enables many exotic plants to flourish. Species from
Australasia are well adapted to conditions in many parts
and a number of Australian plants are 'naturalised' in some Irish gardens.
One of the most popular of these is the genus Eucalyptus. Eucalyps are widely
planted in milder areas because of their many attractive features. These include
beauty of foliage, bark and flowers, speed of growth and scent. Eucalyptus trees
are free from practically all the pests and diseases that affect them in
and so the foliage usually remains completely blemish-free except for wind
scorch towards the end of the winter.
Eucalyptus gunnii is the most widely planted because of its reputation
for hardiness. Other species grown in
are E. johnstoni, E. urnigera, E. viminalis, E. delegatensis and E.
globulus (Morley, 1979). Other species that have survived and continue to
thrive in the climate of the
are E. coccifera, E. pauciflora, E.parvifolia, E. vernicosa and E.
niphophila (Penfold et al, 1961).
Evans (1983) has classified 25 eucalyptus species that have grown in
into the following categories:-
Very hardy - likely to survive long cold spells of -10 C to -14 C. or
short periods down to -18 C E. debeuzevillei, gunnii, parvifolia,
niphophila and perrineana.
Hardy - as above, but unlikely to survive colder than -16 C. E. archeri,
coccifera, glaucescens and vernicosa.
Moderately hardy - likely to survive long cold spells of -
, or short periods down to
-16 C. E. aggregata, dalrympleana, delegatensis, nitida, pauciflora,
stellulata, subcrenulata and urnigera.
Less hardy - likely to survive long cold spells down to -6 C or short
periods down to -9 C. E. cordata, fraxinoides, globulus, johnstoni,
nitens, nicholi, pulverulenta and viminalis.
However, some 500 species of Eucalyptus are recognised (Bean, 1973) ranging
from tall trees to shrubs and small, stunted plants. Because only a small number
of possible eucalypts have been tested in
Ireland, a wider range was examined for their
hardiness and suitablilty as ornamental trees. Moreover, as pointed out by
Penfold and Willis (1961), although the importance of eucalypts to Irish
forestry is small,
is a useful testing ground, where the behaviour of eucalypts may provide much
useful information about climatic adaptability.
Materials and methods
Between 1969 and 1980, seedlings of 102 different eucalyptus species were
planted in a coastal garden Earlscliffe, located on the Howth peninsula just
(53.4 N latitude and 6 W longitude). For details of the situation of the garden
and soil type see Robinson (1992).
Seed, obtained mainly from Kew Gardens London, Mr F.W.Walker, Department of
and Mr A.H.Crane, Chief Commissioner, Forestry Commission,
was sown in a peat compost at Kinsealy Research Centre,
usually in February or March. The seedlings were transplanted to peat pots when
large enough to handle and were planted out in their final position usually in
June or July of the same year when they were 150 - 300 mm high.
The eucalypts tested included species from
New South Wales,
Western Australia. The following species (usually three
seedlings of each) were planted:- E. acaciaeformis, aggregata, alba, albida,
amygdalina, andreana, astringens, baxteri, bicostata, blakelyi, blaxlandi,
bridgesiana, caesia, calophylla, camalduensis, campaspe, camphora, carnea,
cinerea, citriodora, cladocalyx, coccifera, cordata, cordieri, cornuta,
dalrympleana, deanei, delegatensis, diversifolia, doratoxylon, elaeophora,
eremophila, erythronema, falcata, fastigata, ficifolia, forrestiana, glaucescens,
globulus, gomphocephala, goniocalyx, grossa, guilfoylei, gunnii, huberiana,
jacksoni, johnstoni, kitsoniana, kruseana, laevopinea, lansdowneana, lehmanni,
leucoxylon, linearis, longifolia, macarthuri, maculata, maideni, McKieana,
macrorrhynca mitchelliana, neglecta, nicholi, nortoni, notabilis, niphophila,
nitens, notabilis, nova anglica, nutans, obliqua, oblonga, obtusifolia var.
Dendromorpha, occidentalis, ovata, parvifolia, pauciflora var. Bothwell,
peperita, perrineana, polyanthemos, preissiana, pulverulenta, punctata, radiata,
regnans, resinifera, risdoni, rubida, saligna, simondsi, steedmanii, stellulata,
stricklandi, stricta, stuartiana, sturgessiana, tenuiramus (tasmanica),
tetraptera, urnigera, viminalis, wandoo and woodwardi.
The eucalyptus were kept weed free mainly by two applications of simazine at
1.7 kg/ha each year applied in April and July, plus spot treatment of other
appropriate herbicides as required. [*]The heights of surviving trees were recorded
in the early years. It became necessary to reduce the size of most of the trees
because of their rapid growth and height measurement was discontinued.
Minimum air temperatures were recorded at Earlscliffe and meteorological data
were recorded at Danesfort, Baily, about 400 m due north of the test site.
For general information on the climate in Baily see Robinson (1992). The
lowest temperature recorded during the period was -6.0 C, which occurred on a
number of nights in the period 31 December 1978 - 3 January 1979 and on 13/14
January 1987. Low temperatures of - 5.0/5.5 C were recorded on a number of other
occasions, but some winters were very mild. Typical figures for lowest minimum
air temperatures for a five year period are shown in Table 1.
Table 1 - Lowest minimum air temperature ( C) recorded each month at
Danesfort, Baily, Co
As expected, a number of the Eucalyptus species failed to survive their first
winter after planting. This applied particularly to those species from warmer
Australia, such as E. citriodora from
Plants of the very attractive Western Australian eucalypt E. ficifolia
planted in June 1972 were killed in the following winter. One of two plants
overwintered under glass and planted out in May 1973 blossomed between September
and November, 1976 with flowers of a good red colour. This tree was badly
damaged during the 1976/77 winter and, although it made some recovery during the
1977 summer, it died subsequently.
Many other tender Eucalyptus species were killed by the unusually prolonged
cold spell during the period
31 December 1978 -
3 January 1979 . This
cold period killed all the surviving species from
except E. kruseana and cornuta but these species also died
subsequently. The Western Australian species that died during this period or
earlier included E. astringens, calophylla, campaspe, carnei, cornuta,
doratoxylon, eremophila, erythronema, falcata, forrestiana, gomphocephala,
grossa, jacksoni, lehmanni, leucoxylon, nutans, occidentalis, preissiana,
steedmanii, stricklandi, tetraptera and woodwardi.
Many other species died in the early 1980s, but in June 1992, 16 to 23 years
after planting, 37 species still survive. Of the species tested in Baily
the following appear to be the most hardy:- E. acaciaeformis, aggregata,
blaxlandi, camphora, cinerea, cordata, coccifera, cordieri, dalrympleana,
delegatensis, fastigata, glaucescens, globulus, goniocalyx, gunnii, johnstoni,
kitsoniana, linearis, niphophila, nitens, ovata, parvifolia,
pauciflora, perrineana, pulverulenta, risdoni, stellulata, tenuiramis (tasmanica),
urnigera and viminalis. Somewhat less hardy, although still
surviving after 20 years are:- E. baxteri, blakelyi, camalduensis. elaeophora,
laevopinea, nicholi and polyanthemos. All the species in the
most hardy group are native of
New South Wales
and those in the less hardy group are native of
New South Wales
. No species endemic in
survive, although E. pauciflora and viminalis occur in
as well as
New South Wales
Growth of most of the species that survive is rapid compared with native
trees. Some tree heights measured in October 1975 from seed sown in February of
a previous year are as follows:- after 4 seasons E. parvifolia 4 m; after
5 seasons E. maideni 8.4 m, E. cordata 9 m, E. pauciflora var
Bothwell 7 m, E. dalrympleana 7 m; after 7 seasons E. goniocalyx
6.7 m, E. delegatensis 8 m, E. johnstoni 8 m, E. urnigera 8
No serious problems occurred with pests or diseases. Occasionally aphides and
the Blue Gum Psylla (Ctenarytaina eucalypti) occurred, particularly on
E. pulverulenta, but caused little damage.
The major factor influencing the survival of eucalypts is the minimum winter
temperature and not spring frosts, but many other factors are involved (Martin,
1948). Seed provenance is important, but so also are soil conditions, for plants
will stand a lower temperature on a well-drained site better than on a poorly
Weather conditions prior to the onset of a cold period are also relevant. If
the eucalypts are gradually exposed to low temperatures in the autumn and early
winter, they will withstand frost conditions more effectively than if the
temperature drops rapidly before any 'hardening off' process occurs.
None of the species listed as hardy in Evans' (1983) classification was
killed in this study and the results of the trial are in general agreement with
his groupings although not all the species listed by Evans were included in this
The results suggest that a number of additional species are worthy of testing
in mild areas of Britain
to obtain further information on their hardiness.
The following should be included in future trials:-
E. acaciaeformis, blaxlandi, camphora, cinerea, cordieri, fastigata,
goniocalyx, kitsoniana, linearis, ovata, polyanthemos, risdoni, and
tenuiramis, as all have survived temperatures as low as -6 C.
In addition to the species normally grown in
and to those listed by Evans (1983), there are several relatively hardy
eucalypts that would appear to have especial merit as garden plants. Four
attractive species not previously mentioned in the available literature on
E. acaciaeformis, cinerea, kitsoniana and linearis.
E. acaciaeformis. In
this eucalypt grows into an attractive tree with small glaucous leaves about
50 x 20 mm. Although it grows up to 25 m in its native
New South Wales
, it can easily be maintained as a small ornamental garden tree 3 to 4 m tall
by judicious pruning.
E, cinerea. This species, from
New South Wales
, has attractive glaucous, blue-grey foliage and rough fibrous bark on the
trunk, but not on the branches. it does not make a large tree and is highly
E. kitsoniana. This tree grows to about 5 m and is notable for its
bright green foliage and prolific flowering from sessile buds usually in large
clusters of seven.
E. linearis. This attractive species has light green, long, linear
leaves, approximately 70 x 5 mm and with a strong peppermint smell. It makes a
graceful tree about 6 m tall with a light crown.
The State of
is noted for the large number of attractive ecualypts with brilliant coloured
flowers including red, pink, orange and yellow. The results in this trial
suggest that none of these would be sufficiently hardy for growing in
. Nevertheless the fact that E. ficifolia did survive for several years
and flowered in 1976 suggests that there might be opportunities for hybridising
it with a more cold tolerant species. The natural climate could be used to
eliminate the less hardy seedlings, and the survivors screened for their
The results show that a wider range of eucalyptus species than had previously
been tested will grow satisfactorily in mild areas in
Ireland and planting of further Eucalyptus
Bean, W.J., 1973. Trees and shrubs hardy in the
British Isles . Eight Edition. M.Bean and John
Murray (Publishers Ltd.)
50 Albemarle Street,
Evans, J., 1983. Notes on growing Eucalyptus in
. Forestry Commission Booklet 50. HMSO, 49 High Holborn,
WC1V 6HB. pp31.
Martin, D,, 1948. Eucalyptus in the
British Isles . Australian Forestry 12, 64-74.
Morley, B.D., 1979. The contribution of southern hemisphere plants to
Irish gardens. Irish gardening and horticulture, (Eds. C. Nelson and A.
Brady), Royal Horticultural Society of Ireland,
Penfold, A.R. and Willis, J.L.,1961. The Eucalypts. Botany, chemistry,
cultivation and utilization. Leonard Hill Books Ltd.
9 Eden Street,
Robinson, D.W., 1992. Increase of cold hardiness of Echium pininana
through natural selection. ISHS Symposium on Selection and breeding of woody
ornamentals. Acta Horticulturae (In press).
[* Footnote. Since this article was written, the
herbicide, simazine, has been banned in Europe under Commission Decisions
2004/141/EC(3), 2004/248/EC(4), 2004/140/EC(5) and 2004/247/EC(6), taken within
the framework of Council Directive 91/414/EEC of 15 July 1991. This came into
effect on 26th April 2004.]