I\U I I Potential for eucalyptus mulch used as a component
i _- 1 3 of potting mixes for foliage plant production
R.T. Poole and C.A. Conover'
University of Florida, IFAS
Central Florida Research and Education Center Apopka
CFREC-Apopka Research Report, RH-91-13
eP 3 0 199
Pine bark is currently the most widely utilized lumber industry product fo -Ifipi
Since pine bark is a versatile commodity utilized by more than one industry, competition
sometimes makes it unavailable and more substitutes are needed. Several other types of tree
products such as hardwood bark, woodchips, melaleuca bark and shredded melaleuca trees are
also successfully used as potting mix ingredients.
Many acres of eucalyptus trees, native to Australia, were planted for timber, on an
experimental basis, in southwestern Florida. Unfortunately, the hard freezes Florida experienced
in the last decade reduced the value of much of this crop. While the timber is not suitable for
use as lumber, many stands are being converted into a high quality mulch used by the
environmental plant industry. Whole trees are shredded, during the manufacturing process, into
particles small enough to pass through 1 inch screens. The following experiment compared the
Plants were graded based on a scale of 1 = poor quality, unsalable, 3 = fair quality, salable
md 5 = excellent quality plants.
Results and Discussion
The three plants responded differently to the various potting mixes. Compact Boston
Ferns receiving the highest grades were grown in the mixes made up completely or mostly of
Aine bark, although statistically they were no different than ferns grown in all the mixes
:omposed of eucalyptus mulch and Florida sedge peat. Plants in the mix composed entirely of
eucalyptus mulch received the lowest grades (Table 1). Dwarf bananas and red-veined prayer
plants grew best in mixes composed of at least 2:1 (by volume) Florida sedge peat regardless
)f the other components making up the mix. Dwarf bananas and red-veined prayer plants grown
n mixes containing less than 2:1 by volume or no Florida sedge peat received the lowest plant
grades. All plants grown were determined to be of salable quality.
Dwarf bananas and red-veined prayer plants generally grew tallest in the mixes containing
it least 2:1 (by volume) Florida sedge peat and mixes composed Florida sedge peat and pine
)ark (Table 2). Overall, tallest compact Boston fern were generally grown in media containing
Florida peat sedge and eucalyptus bark. The medium made up entirely of coarse eucalyptus
nulch produced the shortest compact Boston ferns and dwarf bananas, while the shortest red-
veined prayer plants were grown in 100% pine bark.
The mixes containing at least 2:1 (by volume) bark and/or eucalyptus mulch had higher
pH and lower electrical conductivity readings than mixes composed of over 2:1 (by volume)
Florida sedge peat (Table 3). The best and worst quality ferns were grown in 100% pine bark
nd 100% coarse eucalyptus, respectively-the two mixes with the lowest leachate electrical
conductivity readings. While pH and electrical conductivity measurements can be good
indicators of medium fertility and nutrient availability, medium physical characteristics also
influence plant growth. The mix composed of 100% coarse eucalyptus bark was very porous
nd did not retain enough water to prevent drying out between waterings.
Several types of composted wood products are currently utilized as medium amendments
in combination with sedge peat in order to moderate the acidity of the peat (raise the pH), to
provide some aeration and to reduce costs. The results of this experiment indicate that
eucalyptus mulch can be successfully used as a component in potting mixes and may serve as
i substitute for pine bark. An earlier study (5) indicated eucalyptus bark may contain toxic
substances and should be composted before use, but the eucalyptus mulch used in this test did
not seem to contain any substances harmful to the three foliage plants tested.
1. Conover, C.A. and R.T. Poole. 1983. Utilization of Melaleuca quinquenervia as a
potting medium component for greenhouse production of foliage plants. HortScience
Forster, W.J., R.D. Wright, M.M. Alley and T.H. Yeager. 1983. Ammonium
adsorption on a pine-bark growing medium. J. Amer. Soc. Hort. Sci. 108(4):548-551.
3. Gartner, J.B., T.D. Huges and J.E. Klett. 1972. Using hardwood bark in container
growing mediums. Amer. Nurseryman 135(12):10-11, 77-79.
4. Ingram, D.L. and C.R. Johnson. 1983. Melaleuca: an alternative container media
component for woody ornamentals. Proc. Fla. State Hort. Soc. 96:254-256.
5. Lunt, O.R. and H.C. Kohl. 1959. Horticultural applications for bark and wood
fragments. Forest Products J. 9:39A-42A.
5. Poole, R.T., C.A. Conover and J.N. Joiner. 1981. Soils and potting mixtures. Chapter
in textbook, Foliae Plant Production, J.N. Joiner, editor, Prentice-Hall Inc. Englewood
Cliffs, NJ 07632. pp 179-202.
7. Poole, R.T. and W.E. Waters. 1972. Evaluation of various potting media for growth
of foliage plants. Proc. Fla. State Hort. Soc. 85:395-398.
3. Sterrett, S.B. and T.A. Fretz. 1977. Effect of nitrogen source and rate on composted
hardwood bark media and subsequent growth of cotoneaster. J. Amer. Soc. Hort. Sci.
'able 1. Plant grade ot tree species grown m meala composer o0 vanous comumiauuis
of Florida sedge peat, pine bark and eucalyptus bark, from 16 April until 9 July
'Bostoniensis Musa acuminata Maranta leuconeura
Ingredients (vol) Compacta' 'Dwarf Cavendish' erythroneura
FPY 4.4abx 4.7a 4.labc
FP:EUC-1, 2:1 4. bc 4.3ab 4.2ab
FP:EUC-1, 1:2 4.3ab 4.5ab 3.3d
FP:EUC-2, 2:1 4.4ab 4.5ab 4.4a
FP:EUC-2, 1:2 4.3ab 4.4ab 3.8abcd
EUC-2 3.7c 3.8c 3.5cd
FP:PB, 2:1 3.8c 4.5ab 4.3a
FP:PB, 1:2 4.6a 4.5ab 4.labc
PB 4.6a 4.2bc 3.6bcd
Plants were graded on a scale of 1 = poor quality, unsalable, 3 = fair quality, salable and 5
= excellent quality.
FP = Florida sedge peat, PB = pine bark, EUC-1 = fine eucalyptus mulch (particles passed
through a 1/2 inch screen), EUC-2 = coarse eucalyptus mulch (particles passed through a 1
Mean separation in rows by Duncan's multiple range test, 5% level.
Height and width (cm) of three species growing in media composed of various
combinations of Florida sedge peat, pine bark and eucalyptus mulch, from 16
April until 9 July 1991.
'Bostoniensis Musa acuminata Maranta leuconeura
Compacta' 'Dwarf Cavendish' erythroneura
Ingredients (vol) Height Width Height Width Height Width
FPZ 35cy 74b 73d 75a 38d 62c
FP:EUC-1, 2:1 33bc 67b 66b 70a 34b 58bc
FP:EUC-1, 1:2 36c 71b 64b 70a 35bc 51ab
FP:EUC-2, 2:1 33bc 72b 70c 70a 38d 57bc
FP:EUC-2, 1:2 35c 68b 66b 70a 35bc 52ab
EUC-2 28a 55a 58a 62a 34b 58bc
FP:PB, 2:1 29ab 68b 70c 74a 38d 50ab
FP:PB, 1:2 32abc 65b 67bc 73a 36bc 48a
PB 3labc 63ab 65b 68a 30a 44a
:al conductivity (jmhos/cm) and pH of leachate from pots containing
leDis exaltata 'Bostoniensis Compacta'. 30 April 1991.
Ingredients (vol) pH /xmhos/cm
FPZ 5.6a 3042a
FP:EUC-1, 2:1 7. c 1250cd
FP:EUC-1, 1:2 7.5c 678e
FP:EUC-2, 2:1 7.0c 1590c
FP:EUC-2, 1:2 7.5c 667e
EUC-2 7. c 713e
FP:PB, 2:1 5.8b 2460b
FP:PB, 1:2 6.5c 1153d
PB 6.8c 461e
Florida sedge peat, PB = pine bark, EUC-1 = fine eucalyptus mulch (particles passed
;h a 1/2 inch screen), EUC-2 = coarse eucalyptus mulch (particles passed through a 1
separation in rows by Duncan's multiple range test, 5% level.