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-/7 Observations of Eucalyptus Cold Tolerance 1985-86 Winter:
Species and Fertilization
R. H. Stamps j Ctra Science
University of Florida, IFAS Librar
Agricultural Research and Education Center Apopka
AREC-Apopka Research Report RH-86-170CT i 4 1987
The genus Eucalyptus, with over 500 species (4), contai hs qalaWrfe mbers
that are popular landscape plants (11) and/or sources-0fcu-t-fo-4age---fo
use by florists and interior designers (3). Lack of adequate cold
tolerance is one of the factors limiting the more widespread use of these
attractive plants. For example, commercial plantings of E. cinerea
(silver-dollar tree) for cut foliage use and a trial planting of 42
eucalyptus species for forestry use have been badly damaged in central
Florida during recent winters.
Cold-hardy eucalyptus should exist since they grow in the coldest areas
of the southernmost mountains and highlands of Tasmania (8). The island of
Tasmania, with elevations over 5,000 feet, receives the majority of
Australia's snowfall (2). In fact, E. neglecta (Omeo rouna-leaved gum)
was included in the following cold toTerance trial because plants of this
species had survived the winters of 1980-81 (approximate low 18"F) and
1981-82 (approximate low 21F) in Sumter Co., Florida, relatively undamaged
(6). Additionally, cuttings of E. neglect have been shown to have
acceptable (1-3 week) vase life T6,7) and to respond positively to the use
of floral preservatives (7). Eucalyptus neglect also appears to be
disease resistant (10) which may help decrease cold damage. Eucalyptus
gunnii (cider gum) was also included in this study because it is reportedly
more cold tolerant than E. cinerea (1), has withstood at least 11'F in
Australia (8), and is used by the florist and landscape industries.
Eucalyptus cinerea, a popular ornamental eucalyptus, was used as a standard
In spite of the common belief that high nutrition predisposes plants to
winter injury, an analysis of the literature indicates that this concept is
not entirely justified (9). Studies have indicated that fertilization with
a complete (NPK) fertilizer may increase cold tolerance in some plants (5,
This study was undertaken to observe the cold tolerance of the three
eucalyptus species listed above when grown under central Florida
conditions. In addition, the effects of fertilizer level on cold tolerance
were also noted.
Materials and Methods
All plants were grown in the ground in Millhopper fine sand under full
sun conditions in a completely randomized design. Plants were irrigated
using one 360" spray nozzle (Maxijet, Thayer .Industries, Dundee, FL 33838)
Assistant Professor of Ornamental Horticulture, Agricultural Research and
Education Center, 2807 Binion Road, Apopka, FL 32703.
per tree when tensiometer (Irrometer Co., Riverside, CA 92506) readings in
the root zone reached -30 (winter) or -15 centibars (spring, summer, and
fall). The 4-year old E. neglecta and E. cinerea plants observed in this
study were clonal (each-species propagated vegetatively from a single stock
plant), and well established prior to the onset of cold weather since they
had been planted 8 March 1983. The E. gunnii plants were propagated from
seed and were not so well established as the other species since they were
transplanted 7 August 1985 from one gallon containers.
Fertilizer treatments, initiated 26 September, were 300 or 600 1b
N/acre/year obtained using bimonthly applications of Sierrat 17-6-12
controlled release fertilizer (Sierra Chemical Co, Milpitas, CA 95035).
The fertilizer was applied to a 22 ft square area under each tree.
Treatments were replicated 7-8 times for E. gunnii and E. neglecta, and 3-4
times for E. cinerea. Temperatures were recorded using a hygro-thermograph
(Model 594, Bendix, Baltimore, MD 21204) and a National Weather Service
mercury minimum temperature thermometer. Wind speeds were supplied by the
Two subfreezing temperature periods occurred at the test site during
the winter of 1985-86. The first from 25-27 December consisted of 23.5
hours of sub 320F temperatures, wind speeds of 3.5 to 15 mph, and low dry
bulb and dew point temperatures of 20 and 2F, respectively. The second
freeze occurred in January on the night of the 27th and the morning of the
28th. Temperatures remained below freezing for 13 hours, wind speeds were
5 to 12 mph, and dry bulb and dew point temperatures reached lows of 22
and 2F, respectively.
Above ground portions of plants were rated on 31 December, 10 February,
and 14 April for cold damage using a rating scale of 0 = no damage, 1 =
slight damage (damage to some tender foliage only, virtually all foliage
still salable as cut foliage), 2 = moderate damage (immature and some
mature foliage damaged), 3 = severe damage (no marketable stems), and 4 =
complete necrosis. Additional observations were made regarding plant
regrowth from the stem base.
Results and Discussion
Eucalyptus cinerea sustained severe damage to above ground plant parts
(Table 1). However, about 70% of the plants survived and regrew from the
ground. Eucalyptus gunnii survived the first freeze with only slight
damage. Unfortunately, three E. gunnii plants (1 low and 2 high
fertilizer) that had survived the second freeze with virtually no cold
damage died before the April ratings due to stem breakage and girdling
caused by high winds. Of the remaining E. gunnii, 25% of the plants
survived the second freeze with very slight damage and the remainder were
killed. The variability in cold tolerance results may be due to genetic
differences .since these plants were grown from seed, or to temporal
differences in physiology or maturity of the plants. The E. gunnii plants
that sustained little damage from the two cold stress periods were the
largest plants of that species. Eucalyptus neglect was tolerant of the
temperatures occurring during the 1985-86 winter. Direct comparison of the
three species is not possible due to differences in plant age, size, and
time in the ground. However, the fact that some E. gunnii and all E.
neglecta plants sustained little or no damage is encouraging.
RH-86-17, page 2
Although the cold damage ratings in every case but one were numerically
lower (less damage) for plants fertilized at the higher rate for each
species at each rating, none of these differences were statistically
significant (P<0.54 to 0.09). However, these data suggest that by using
higher fertilizer rates and/or more replications, significant differences
in cold tolerance due to fertilizer treatments may be detectable.
(An additional observation was made at this eucalyptus planting: Three
young E. nicholii (narrow-leaved black peppermint) plants being grown at
the 300 lD N/A/yr rate were severely damaged, but one of the plants
sprouted from the ground and survived the winter.)
1. Allemand, P. and E. Berninger. 1985. Les degats du froid aux arbres
et arbustes d'ornement du littoral mediterrangen. P.H.M.-Revue
Horticole, No. 259:45-48.
2. Anonymous. 1972. Australia. Collier's Encyclopedia.
3. Auman, C. W. 1980. Minor cut crops, p. 183-216. In: R. A. Larson
(ed.). Introduction to floriculture. Academic Press, New York, NY
4. Bailey, L..H. and E. Z. Bailey. 1976. Hortus Third. MacMillan
Publishing Co., Inc., New York, NY 10022.
5. Gilbert, W. B. and D. L. Davis. 1971. Influence of fertility ratios
on winter hardiness of bermudagrass. Agron. J. 63:591-593.
6. Henny, R. J., R. H. Stamps, and E. M. Rasmussen. 1982. Preliminary
evaluation of different Eucalyptus species for use as a cut-foliage
crop: II. Increasing postharvest vase-life of cut stems using a
floral preservative. Univ. of Fla., Agr. Res. Cntr.-Apopka Res. Rpt.
7. Henny, R. J., R. H. Stamps, and E. M. Rasmussen. 1982. Preliminary
evaluation of different Eucalyptus species for use as a cut-foliage
crop: I. Postharvest vase-life of cut stems. Univ. of Fla., Agr.
Res. Cntr.-Apopka Res. Rpt. RH-82-5.
8. Jones, J. 1980. Eucalyptus indoors. Horticulture LVIII(12):52-57.
9. Pellett, H. M. and J. V. Carter. 1981. Effect of nutritional factors
on cold hardiness of plants, p. 144-171. In: J. Janick (ed.).
Horticultural reviews, vol. 3. AVI Publishing Co., Inc., Westport, CN.
10. Stamps, R. H. 1986. Cut foliage crops for Florida. Univ. of Fla.,
Agr. Res. and Ed. Cntr.-Apopka Cut Foliage Res. Note RH-86-A.
11. Sunset Books. 1979. J. R. Dunmire (ed.). Sunset New Western Garden
Book, 4th Edition. Lane Publishing Co., Menlo Park, CA 94025.
RH-86-17, page 3
12. Zurawicz, E. and C. Struchnoff. 1977. Influence of nutrition on cold
tolerance of 'Redcoat' strawberries. J. Amer. Soc. Hort. Sci.
Table 1. Cold damage ratings of 3 eucalyptus species grown at 2
Fertilizer Cold damage ratingy (% regrowthx)
Eucalyptus rate --------------------------------- Survival
species (lb N/A/yr) 12/31/85 02/10/86 4/14/86 (%)
cinerea 300 3.00w 3.33 4.00 (67) 67
600 2.50 3.00 3.50 (75) 75
gunnii 300 1.25 2.25 3.33 (17) 17
600 0.94 1.10 2.60 ( 0) 33
neglect 300 0.10 0.44 0.00 ( 0) 100
600 0.05 0.11 0.13 ( 0) 100
zObtained using bimonthly applications of Sierra" 17-6-12 fertilizer.
YO = no damage, 1 = slight damage, 2 = moderate damage, 3 = severe damage,
and 4 = total necrosis of above ground plant parts.
XVegetation sprouting from below ground plant parts.
Fertilizer treatments had no significant effect (at the 5% level) on cold
damage ratings for any species at any rating date.
RH-86-17, page 4