Some foliage plants have specific potting medium requirements, but most grow well in a variety of potting mixtures, and thus, there is no single best growing medium for foliage plants. High quality potting media produce quality plants, in the shortest time, with the lowest total production costs. Potting medium components should be readily available to growers, inexpensive, uniform, and sterile.

Most potting mixtures are blends of two or more materials. Good quality sphagnum peat moss or sedge peat moss, vermiculite, builders' sand, and pine bark are four popular ingredients used today. Unfortunately, these, and other popular potting medium amendments are becoming more costly and less readily available to the foliage plant industry. Growers are looking for less expensive potting medium amendments to replace, in part, the more expensive ingredients in their mixes. They want more information on new potting medium amendments because any amendment added to a potting medium will affect its physical characteristics and plant growth.

Compro, a woodchip sewage sludge compost, manufactured by Maryland Environmental Service, 60 West Street, Annapolis, Maryland, was shown to be a satisfactory ingredient of potting media in a preliminary experiment. Compro is produced by mixing sewage sludge with woodchips, then composting this mixture at temperatures well into the pasteurization range, up to 180F. The compost-woodchip mixture is then screened to eliminate large woodchips. Compro has a pH of 6.8-7.4. The composted sludge is dense, with a dry weight of 40 lb/ft , and has a water-holding capacity of 225% by weight. Two experiments were conducted to determine growth of 4 foliage plants in various potting media with different levels of Compro incorporated. The physical characteristics of these media were also determined. These media physical characteristics have already been published (Proc. Fla. State Hort. Soc. 98:92-94, 1985) and will not be mentioned here.

Experiment 1, initiated June 24 utilized 3 base potting media which were (1) 3 Florida peat:1 builders' sand; (2) 2 Florida peat:1 pine bark:1 cypress shavings; and (3) 1 Florida peat:1 pine bark. Five levels of woodchip sludge compost were added to make up 0, 10, 20, 30, or 40% of the above media. The resulting 15 potting mixes were amended with 1.5 lb/yd Micromax and 7 lbs/yd3 dolomite. Micromax is a micronutrient blend manufactured by Sierra Chemical Co., Milpitas, CA. These mixes were then used to grow rooted cuttings of Dieffenbachia maculata (dieffenbachia) and Peperomia obtusifolia (oval-leaved peperomia) in 6 inch standard pots.

Osmocote 19-6-12, manufactured by Sierra Chemical Co., Milpitas, CA, was surface applied at 2 grams per pot for Peperomia and 3.3 grams per pot for Dieffenbachia, on June 24 and Sept 26. Plants were grown in a greenhouse receiving 1500 ft-c maximum light and temperatures ranging from 65 to 95°F. Plants were irrigated 2 or 3 times weekly. On Oct 24, experiment 1 was terminated and the following data were determined: plant height, plant quality, rated on a 1 (poor, not salable) to 5 (excellent quality) scale; and root grade rated on a 1 (0-20% root ball coverage) to 5 (81-100% root ball coverage) scale.

Experiment 2 soil treatments were the same as those in experiment 1. Brassaia actinophylla (schefflera) and Chrysalidocarpus lutescens (areca palm) were placed in 8 inch pots on July 9 and fertilized with 9.5 grams and 7.0 grams respectively, of 19-6-12 Osmocote on July 9 and Oct 14. Plants were grown in a shadehouse receiving 6,000 ft-c maximum light with temperatures ranging from 50 to 98°F. Growth data for Brassaia were taken on Dec 8; for Chrysalidocarpus on Feb 8. Plant height and quality were determined as were color grade rated on a 1 (light green) to 5 (dark green) scale.

Dieffenbachia and Peperomia grown in 3 Florida peat:l builders' sand (base medium) were slightly taller and of higher quality than plants grown in the 2 other base media, but root grade was reduced (Table 1). Brassaia and Chrysalidocarpus grew equally in the 3 base media (data not shown). Additions of Compro to these 3 base potting media had no influence on the height or quality of plants grown All plants qrown were of good salable quality. These experiments demonstrate that media composed of 10 to 40% Compro can be used without reducing quality of the plants tested.

*Professor, Plant Physiology and Center Director and Professor, respectively, Central Florida Research and Education Center, 2807 Binion Road, Apopka, Florida 32703-8504.

1. Chase, A. R. and R. T. Poole. 1985. Root Rot. Greenhouse Manager 4(2):142, 145, 146, 149.

2. Conover, C. A. and R. T. Poole. 1978. Influence of Florida humate on foliage plant growth. Proc. Soil and Crop Sci. Soc. Fla. 38:5-7.

3. Fonteno, W. C., D. K. Cassel, and R. A. Larson. 1981. Physical properties of 3 container media and their effect on poinsettia growth. J. Amer. Soc. Hort. Sci. 106:736-741.

4. Joiner, J. N. and C. A. Conover. 1965. Characteristics affecting desirability of various media components for production of container-grown plants. Proc. Soil and Crop. Sci. Soc. Fla. 25:320-328.

5. Poole, R. T. and C. A. Conover. 1977. Influence of medium, container size and water regime on growth of Pellionia pulchra N. E. Br. and Pilea involucrata (SIMS) URB. Proc. Fla. State Hort. Soc. 90:319-320.

6. Poole, R. T., C. A. Conover, and J. N. Joiner. 1981. Soils and potting mixtures, p. 179-202. In: J. N. Joiner (ed.). Foliage plant production. Prentice-Hall, Inc., Englewood Cliffs, N.J.

^Z1 = poor, not salable, 5 = excellent quality.
^Y1 = 0-20% root ball coverage, 5 = 81-100% coverage.
^X3 Florida peat:1 builders' sand; 2 Florida peat:1 cypress shavings:1 pine bark; 1 Florida peat:1 pine bark.