Large quantities of low quality sedge and highly oxidized sphagnum peats exist in the United States. This peat is generally unsuitable for use as growing media unless amended with materials to improve aeration. Pine bark, vermiculite, perlite, or styrofoam pellets are coarse materials currently used for this purpose. With these materials becoming more expensive, there exists a need for more economical substitutes.

Melaleuca quinquenervia (punk or paper bark tree) currently has few commercial uses. This Australian import, considered a weed in our country, has invaded over 500,000 acres of southern Florida. Melaleuca can grow on a wide variety of wet or dry, poor or disturbed soils, crowding out native plant material and quickly dominating the landscape. Melaleuca bark comprises up to 50% of the trunk and branch volume and its loose, open structure makes it a potential coarse material for use in potting mixes. The experiments that follow were developed to examine the potential use of shredded Melaleuca bark (MB) and Melaleuca tree mix (MM) as components of potting media for containerized foliage plants.

All Melaleuca bark used was separated from fresh 4 to 6 inch diameter logs, and individual bark fragments ranged in size from dust to 2 inches long with most within the 0.4 to 0.8 inch range. Thickness was less than 0.2 inches. Melaleuca tree mix was composed of the entire above-ground portion of trees measuring 1 to 4 inches in diameter at breast height. Shredded particle sizes were variable, with bark portions similar to the bark listed above, and wood portions mostly 0.1 to 0.2 inches in diameter and up to 2 inches long. Leaf and seed portions of trees were included and were barely noticeable after shredding. All bark and tree materials used were fresh, having aged no longer than 8 weeks. All media tested were first amended with 7 lbs/yd³ dolomitic limestone and 1.5 lb/yd³ of Perk or Micromax (micronutrient blends). Perk, manufactured by Estech General Chemicals Corporation, Chicago, IL, was used in experiments 1 through 4. Experiment 5 media contained Micromax, which is manufactured by Sierra Chemical Co., Milpitas, CA.

Two experiments compared artificial media composed of sedge peat (P), Solite (SO), [a fired Montmorillonite clay particle sized about 0.5 inch, produced by the Solite Corp. of Richmond, VA.], MB and MM, against 3 peat:1 sand (P:S). Experiment 1 utilized 6 to 8 inch liners of Ficus benjamina (weeping fig) and Dracaena marginata (Madagascar dragon tree) potted into 6 inch standard pots. The five potting mixes examined were (1) 3P:1S, (2) 3P:1SO, and (3-5) P:MB:SO in mixtures of 2:1:1, 1:2:1, and 2:1:1 by volume. Six month release rate 18-6-12 Osmocote fertilizer was surface applied at time of potting, Jan. 4, at rates of 3.3 or 6.6 grams per pot. Osmocote fertilizer is manufactured by Sierra Chemical Co., Milpitas, CA. Plants were grown under 47% polypropylene shadecloth where they received a maximum of 6000 ft-c natural light. Temperatures ranged from 45°F to 100°F. Plants were watered once or twice weekly.

On Sept. 2, plant height was measured and plant quality graded on a scale of 1-5 with 1 = poor, not salable; 3 = good, salable; and 5 = excellent quality. Color grade was rated on a 1-5 scale with 1 = light green; 3 = medium green and 5 = dark green.

Different media had less effect on plant grade of Dracaena than that of Ficus. Where MB constituted 50% of the potting mixture, as in the 1P:2MB:1SO, plant height and grade of both Ficus and Dracaena were smallest. Where MB made up only 25% of the mix, growth of both plants compared favorably with the 3P:1S standard (Table 1). Doubling fertilizer levels increased height of Dracaena.

Experiment 2 involved growing rooted tip cuttings of Ficus benjamina and Dracaena marginata, one per 6-inch standard pot. Medium treatments included (1) 3P:1S, (2) 3P:1SO, (3) 2P:1SO and (4-6) P:MM:SO in mixtures of 1:1:1, 2:2:1, and 1:2:1 by volume. Fertilizer rates of 4, 8, or 12 grams per pot Osmocote 14-14-14 fertilizer were surface applied Nov. 25, at time of potting. Plants were refertilized 5 months later with 19-6-10 Osmocote at rates of 3.3, 6.6, or 9.9 grams per pot. Plants were grown under 47% polypropylene shadecloth, receiving 6000 ft-c maximum natural light. Temperatures ranged from 45°F to 100°F and plants were irrigated twice weekly. Plant growth data recorded after 8 months for Ficus included height and plant grade, and for Dracaena, height, plant grade, fresh top and root weight.

Growth of Ficus was not affected by media or fertilizer levels (Table 2). Height of Dracaena was greatest in the 3P:1S mix, while plant grade was equal in the 3P:1S, 3P:1SO, 2P:1SO, and 1MM:1SO media. No differences in top or root weights were observed on Dracaena grown in these mixes. As in experiment 1, 1P:2MM:1SO was a poor mix for Dracaena, especially when compared with the 3P:1S standard. Increasing fertilizer levels increased top weight, height, and plant grade of Dracaena. Lack of interactions found in plants' response to the medium-fertilizer combinations tested shows increases in fertilizer levels would not correct problems observed with the Melaleuca containing mixes (Table 2 significant effects MxF). Shorter plants, and lower plant grade of Dracaena appear to be caused by too much non-capillary pore space (aeration) and lowered water-holding capacity of the soil mix.

Experiment 3 was conducted to determine growth response of Ficus benjamina (weeping fig) in various combinations of peat, sand, Melaleuca bark, and Melaleuca tree mix, irrigated at different frequencies. Twenty-two inch Ficus plants growing one per pot, in 6 inch pots containing 3 Florida sedge peat:1 builder's sand by volume, were repotted into 10 inch containers on June 16, using the twelve listed potting medium combinations (Table 3). Containers were surface treated with 9 grams per pot 18-6-12 Osmocote fertilizer every three months, for a total of 3 times. Plants were grown in a polypropylene shadehouse where they received 4500 ft-c natural light. Temperatures ranged from 54°F to 95°F and plants were watered 2 or 4 times per week.

On Feb. 10, plants were sleeved, boxed, and placed in coolers with 55°F temperature and 85% RH (relative humidity). Plants were removed from shipping chambers after 4 weeks and placed in rooms where they received 75 ft-c light from cool white fluorescent lamps 12 hours daily. Temperature was maintained at 77°F and RH was 60%. Plants were watered once a week or as needed.

Data recorded May 27, on termination of experiment 3, included height, fresh weight and plant grade as in experiment 1, and root grade (based on a quality scale of 1-5 where 1 = 0-20%, and 5 = 81-100% root ball coverage). Plant height was not affected by percentage of MM in soil mix, but percentage of MM in mix did influence other plant characteristics. Fresh weight, plant grade, and root grade increased as Melaleuca content of the media decreased. More frequent waterings increased fresh weight and root grade, but did not affect plant grade or height (Table 4). These results agree with experiments 1 and 2, suggesting media composed of no more than 25% by volume MB and/or MM can be used to grow good quality foliage plants if other media components do not have a high water-holding capacity.

Experiments 4 and 5 examined the potential use of shredded Melaleuca tree mix and/or Melaleuca bark as components of growing media for greenhouse production of foliage plants, and compared MB and MM mixes to 2 sedge peat:1 pine bark:1 cypress shavings mix. Both experiments used Aglaonema commutatum 'Fransher' (Fransher aglaonema) and Nephrolepis exaltata 'Fluffy Ruffles' (Fluffy Ruffle Boston fern) potted in 6 inch containers.

Experiment 4, initiated Mar. 5, compared four potting mixes: (1) 2 Florida sedge peat:l pine bark:l cypress shavings (SP:PB:CS) and (2-4) Florida sedge peat:melaleuca bark (SP:MB) in mixtures of 1:1, 3:1, and 1:3 by volume. Plants were fertilized with 3.5 or 7.0 grams per pot 18-6-12 Osmocote and watered 2 or 4 times weekly. Plants were placed in a glass greenhouse where they received a maximum of 1200 ft-c natural light. Temperatures ranged from 64°F to 90°F.

Plant growth data for Boston fern, recorded after 3 months, included plant height and plant grade, based on the same scale as experiment 1, and number of runners (Table 5). Boston fern grew equally well in all media and fertilizer levels had no effect on growth. Height, plant grade, and number of runners produced were greater when watered 4 rather than 2 times per week, but earlier research has also shown that Boston fern responds positively to increased watering levels.

Growth data recorded for Aglaonema after 6 months included height, plant grade, and number of basal breaks (shoots) greater than 1 inch tall. Height and grade of Aglaonema were unaffected by treatment. Lack of interactions in this experiment show the wide range of conditions under which these Melaleuca bark mixes could be useful in greenhouse production. In experiment 5, initiated Feb. 5, Aglaonema and Boston fern watering and fertilizer treatment rates were similar to experiment 4 except 19-6-10 Osmocote Sierrablen fertilizer replaced 18-6-12 Osmocote. Seven media were compared: (1) 2 Florida sedge peat:1 pine bark:1 cypress shavings, (2-4) Florida sedge peat:melaleuca bark in mixtures of 1:1, 1:2, and 2:1 by volume, and (5-7) Florida sedge peat:Melaleuca tree mix in combinations of 1:1, 1:2, and 2:1 by volume. Plants were grown in glass greenhouses under the same conditions as experiment 4.

Plant growth data recorded at 4 months for Boston fern included plant height, plant width, and plant grade as in experiment 4 (Table 6). Growth data recorded for Aglaonema at 6 months included height, plant grade, and number of basal breaks greater than one inch tall.

Height and plant grade of Boston fern, and plant grade and number of shoots on Aglaonema were not affected by media. Plants in mixes containing more than 50% MB or MM were slightly shorter (Aglaonema) or not as wide (Boston fern). Doubling fertilizer rate from 3.5 grams to 7.0 grams per pot increased slightly all growth measurements for Boston fern and Aglaonema but may not be economically worthwhile. Lack of significant irrigation interactions (Table 6 significant effects) shows responses to increased watering relate to all mixes tested and may be due to their high aeration levels.

Experiment 4 and 5 data show MB and MM have great potential for increasing aeration in potting media. Mixes containing more than 50% MB or MM by volume produced the smallest plants probably because aeration levels were too high and the medium dried too rapidly.

Data from all 5 experiments show MB and MM can serve as a component of media used to produce high quality shadehouse and greenhouse grown foliage plants. Up to 50% by volume MB or MM may be used when other components of media have poor aeration and high water-holding capacity. When builder's sand or other materials having a lower water-holding capacity make up to 25% of the growing media by volume, Melaleuca bark or Melaleuca tree mix should not exceed 25% by volume.

Melaleuca bark and Melaleuca tree mix have potential for use in the container plant industry but are not currently being used by most potting mix manufacturers. This situation will continue unless producers ask the potting mix industry to supply mixes containing melaleuca products.

Some of the advantages to using Melaleuca bark and/or Melaleuca tree mix are:

1. Melaleuca's excellent aeration characteristics allow it to be used with high or low quality peat moss.

2. The decomposition rate of Melaleuca is about the same as cypress shavings and pine bark.

3. Melaleuca bark and/or Melaleuca tree mix can be used as a substitute for pine bark. This is especially advantageous for growers shipping foliage plants to Europe since melaleuca meets quarantine requirements and pine bark does not.

4. Melaleuca trees are a renewable resource in south Florida where pine bark is in short supply.

*Center Director and Professor (retired 7/96) and Professor, Plant Physiology, respectively, Central Florida Research and Education Center, 2807 Binion Road, Apopka, Florida 32703-8504.

1. Conover, C. A. and R. T. Poole. 1983. Sedge moss peat, solite, and Melaleuca quinquenervia as potting medium components for shadehouse production of foliage plants. HortScience 18:888-890.

2. Conover, C. A. and R. T. Poole. 1983. Utilization of Melaleuca quinquenervia as a potting medium component for greenhouse production of foliage plants. HortScience 18:886-888.

3. Ingram, D. L. and C. R. Johnson. 1982. Melaleuca bark as a container medium component. Univ. of Fla. IFAS, Orn. Hort. Rpt.

4. Poole, R. T. and C. A. Conover. 1979. Melaleuca bark and solite as potential potting ingredients for foliage plants. Proc. Fla. State Hort. Soc. 92:327-329.

5. Poole, R. T. and C. A. Conover. 1985. Growth of Ficus benjamina in combinations of peat, sand, and Melaleuca. HortScience 20:383-385.

6. 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.

^Zmedia composed of P = peat, S = sand, MB = melaleuca bark, and SO = solite by volume.
^Y1 = poor, not salable; 3 = good, salable; 5 = excellent quality.
^XNS,*,**Nonsignificant (NS), or significant at 5% (*) or 1% (**) level.

^ZMedia composed of P = peat, S = sand, SO = solite, and MM = melaleuca (tree) mix by volume.
^Y1 = poor, not salable; 3 = good, salable; 5 = excellent quality.
^X14-14-14 at 4, 8, 12 grams/pot initially, grams/pot, 5 months later.
^WNS,*,**Nonsignificant (NS) or significant at 5% (*) or 1% (**) level, L = linear; Q = quadratic.

^Z1 = poor, not salable; 3 = good, salable; and 5 = excellent quality.
^Y1 = 0-20%, 3 = 41-60%, and 5 = 81-100% root ball coverage with white healthy roots.

^ZMedia composed of SP = sedge peat, BP = pine bark, CS = cypress shavings, and MB = melaleuca bark.
^Y1 = poor, not salable; 3 = good, salable; and 5 = excellent quality.
^XFrom 18-6-12 6 month Osmocote.
^WNS,*,**,***Nonsignificant (NS) or significant at 5% (*), 1% (**), or 0.1% (***) level.

^ZMedia composed of SP = sedge peat, PB = pine bark, CS = cypress shavings, MB = melaleuca bark, and MM = melaleuca mix.
^Y1 = poor, not salable; 3 = good, salable; 5 = excellent quality.
^XFrom 19-6-10 Osmocote.
^WNS,*,**Nonsignificant (NS) or significant at 5% (*) or 1% (**) level.

---