Composted Household Waste Utilized as a Medium Component in Greenhouse Foliage Plant Production

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University of Florida, IFAS,
Central Florida Research and Education Center - Apopka
CFREC-A Research Report RH-91-6

C.A. Conover and R.T. Poole*

Satisfactory soil mix ingredients developed from processing residues in recent years include pine bark, rice hulls, sugar cane stalks and peanut shells. Unfortunately these products are not universally available so the need for inexpensive medium components still exists. In the United States, growing concern for environmental quality and the rising cost of solid waste disposal has created a climate favorable for recycling projects. Municipal refuse, a widely available material, has been tested for use by the greenhouse industry in the past with mixed results.

Experiments by Conover and Joiner with raw garbage converted to compost within 3 weeks showed that garbage compost could be substituted for peat moss in potted chrysanthemum production. However, the mix composed of 100% garbage compost had higher soluble salts levels and produced poor quality plants compared to other mixes tested which contained a lesser volume or no compost.

The uptake of potentially toxic elements is a major concern when garbage composts are utilized in container media. Earlier experimentation by Gogue and Sanderson using municipal compost as a medium amendment for chrysanthemum culture resulted in accumulation of high levels of potassium, copper, boron and zinc in foliar tissue. A marginal leaf injury on older foliage was also observed in compost grown plants. Boron toxicity and high total salts or pH were possible explanations for the foliar damage.

Processed garbage was also utilized as a soil amendment in a series of tests conducted by Sanderson and Martin with Chrysanthemum morifolium, Antirrhinum majus, Lillium longiflorum and Petunia hybrida. Soil analysis of media containing 25-50% processed garbage revealed low nitrogen, phosphorous and calcium levels, excessively high pH and high soluble salts. The processed garbage underwent a rapid breakdown in greenhouse culture causing nitrogen deficiency symptoms. Leaves of chrysanthemums, snapdragons and petunias often exhibited scorched margins.

Chamaedorea elegans (Parlor Palm) growth response is typical of a number of soluble salts sensitive foliage plants. On the other hand, Dieffenbachia maculata 'Camille' can tolerate a wide range of fertilizer levels and its growth response is typical of a number of soluble salts tolerant plants. The following research involving these two foliage plants with widely divergent soluble salts tolerance was performed to determine the feasibility of utilizing solid waste aerobically composted for 21 days as a medium amendment in foliage plant production.

The compost tested, Agri-soil (Agri-post Inc., Pompano Beach, FL 33061), was manufactured from unseparated household garbage obtained from Dade county's municipal curbside waste pick-up service. The unseparated household solid waste which included tires, glass, plastic and paper was shredded, hammermilled and then composted under aerobic conditions at temperatures above 170F for a 3 week period.

A 9 x 3 factorial experiment was initiated on 16 August 1990 at the Central Florida Research and Education Center, Apopka, Florida. Chamaedorea elegans and Dieffenbachia maculata 'Camille' growing in 3 inch pots were transplanted into 6 inch containers using nine growing media composed of various amounts of Florida peat sedge (P), Agri-soil (AGRI) and pine bark (B). Composition of the tested media by volume is listed in Table 1. Plants were grown in a greenhouse under a maximum of 1500 ft-c and watered three times a week. They were fertilized with 19-6-12 Osmocote 3 month release fertilizer (Grace/Sierra Co., Milpitas, CA 95035) surface applied on 21 August and 30 November 1990 at rates of 3, 6 and 9 g/6 inch pot. Electrical conductivity and pH of the leachate from the media were measured using the pour through method before planting and fertilization, and then monthly for the duration of research. Plant height was recorded initially and at three month intervals and plant grade was determined every three months.

Generally, plants grown in the mixes composed of 30 and 40% Agri-soil and less than 40% peat received lower plant grades than foliage produced in media containing less compost and more peat than pine bark (Tables 1 and 2). The lowest quality plants were produced in mixes containing only 20 and 30% sedge peat.

Fertilizer rate had no effect on growth and quality of Neanthe Bella palms but Dieffenbachia 'Camille' grew taller and received higher plant grades as fertilizer rate increased (Table 2). The best quality Dieffenbachia 'Camille' were grown with 9 grams of 19-6-12 per 6 inch pot, the highest fertilizer rate tested.

Initially the electrical conductivity and pH of leachate significantly increased as percent of Agri-soil increased but no significant differences were found in electrical conductivity of all mixes tested after two months had elapsed (Tables 3 and 4). High levels of soluble salts present at the beginning of experimentation in the media containing 30 and 40% Agri-soil must have been easily leached from the media over time. Fertilizer rate significantly affected leachate electrical conductivity and pH. Electrical conductivity of the leachate increased as fertilization rate rose from 3 to 9 g/6 inch pot and pH. dropped in response to rising fertilizer levels.

In this test and in previous research, composted unseparated municipal waste produced satisfactory greenhouse crops when its presence in media was limited to no more than 20% by volume or 30% by volume if the mix also had a 30% or higher volume of sedge peat. The higher soluble salts levels found in media containing higher percentages of unseparated garbage may have inhibited plant growth at the start of the experiment, especially growth of the salt intolerant parlor palm.

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

Additional Reading

1. Bugbee, G.J. and C.R. Frink. 1989. Composted waste as a peat substitute in peat-lite media. HortScience 24(4):625-627.

2. Conover, C.A. and J.N. Joiner. 1966. Garbage compost as a potential soil component in production of Chrysanthemum morifolium 'Yellow Delaware' and 'Oregon'. Proc. Fla. State Hort. Soc. 79:424-429.

3. Conover, C.A. and R.T. Poole. 1990. Light and fertilizer recommendations for production of acclimatized potted foliage plants. Foliage Digest 13(6):1-6.

4. Gogue, G.J. and K.C. Sanderson. 1975. Municipal Compost as a medium amendment for chrysanthemum culture. J. Amer. Hort. Sci. 100(3):213-216.

5. Hoitink, H.A. and H.A. Poole. 1980. Factors affecting quality of composts for utilization in container media. HortScience 15(2):13-15.

6. Poole, R.T. and C.A. Conover. 1972. Evaluation of various potting media for growth of foliage plants. Proc. Fla. State Hort. Soc. 85:395-398.

7. Sanderson, K.C. and W.C. Martin, Jr. 1968. Utilization of processed garbage as a soil amendment in the production of selected greenhouse crops. HortScience 3(2): 104.

^ZPlants were graded on a scale of 1 = poor quality, unsalable, 3 = fair quality, salable and 5 = excellent quality plant material.
^YMeans in columns followed by the same letter are not significantly different at the 5% level, Duncan's multiple range test.
^X19N-6P₂O₅-12K₂O Osmocote 3 month release rate fertilizer was applied on 17 August and 30 November 1990.
^Wns denotes results showing no significant statistical differences.

^ZPlants graded on a scale of 1 = poor quality, unsalable, 3 = fair quality, salable and 5 = excellent quality.
^YMeans in columns followed by the same letter are not significantly different at the 5% level, Duncan's multiple range test.
^X19N-6P₂O₅-12K₂O Osmocote 3 month release rate fertilizer was applied on 17 August and 30 November 1990.
^Wns, **; Nonsignificant or significant at P = .01.

^ZElectrical conductivity and pH level of the leachate from the media were measured from filled containers without plant material or fertilizer on 24 August 1990. Measurements taken on later dates were obtained from containers holding media, fertilizer and plants.
^YMeans in columns followed by the same letter are not significantly different at the 5% level, Duncan's multiple range test.
^X19N-6P₂O₅-12K₂O Osmocote 3 month release rate fertilizer was applied on 17 August and 30 November 1990.
^Wns, *, **; Nonsignificant or significant at P = .05 or P = .01 respectively.

^ZInitial electrical conductivity and pH level of media leachate were measured from filled containers without plant material or fertilizer on 24 August 1990. The measurements recorded thereafter were taken from containers holding media and growing plants.
^YMean in columns followed by the same letter are not significantly different at the 5% level, Duncan's multiple range test.
^X19N-6P₂O₅-12K₂O Osmocote 3 month release rate fertilizer was applied on 17 August and 30 November 1990.
^Wns, *, **; Nonsignificant or significant at P = .05 or P = .01 respectively.