In the southeastern United States, inconsistent pine bark (PB) supplies and overabundance of cotton gin by-products warrant investigation about the feasibility of replacing PB with cotton gin compost (CGC) for container horticultural plant production. Most research on the use of composted organic substrates for horticultural plant production has focused on shoot growth responses, so there is a need to document the effect of these substrates on root growth. In 2004, `Blitz' tomato (Lycopersicon esculentum), `Hot Country' lantana (Lantana camara `Hot Country'), and weeping fig (Ficus benjamina) were placed in Horhizotrons to evaluate root growth in 100% PB and three PB:CGC substrates containing, by volume, 60:40 PB:CGC, 40:60 PB:CGC, and 0:100 PB:CGC. Horhizotrons were placed in a greenhouse, and root growth in all substrates was measured for each cultivar. Physical properties (total porosity, water holding capacity, air space, and bulk density) and chemical properties (electrical conductivity and pH) were determined for all substrates. Physical properties of 100% PB were within recommended guidelines and were either within or above recommended ranges for all PB:CGC substrate blends. Chemical properties of all substrates were within or above recommended guidelines. Root growth of all species in substrates containing CGC was similar to or more enhanced than root growth in 100% PB.
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