Evaluation of Spent Tea Grinds as an Alternative Horticultural Substrate Component

Abstract

Spent Tea Grinds (STG) is the by-product of the rapidly growing tea brewing industry. Published research to date provides few alternatives for beneficial uses of STG. However, the physical and chemical properties of STG indicate a possibility for use as a suitable substrate component. In response to a request for proposals from the Milo’s Tea Company, Inc., Bessemer, AL, a series of studies were proposed and subsequently funded to evaluate STG as a substrate component for greenhouse and nursery crops. In a greenhouse study, Lantana camara ‘New Gold’ and Nephrolepis exaltata ‘Bostoniensis’ were grown for 10 weeks in seven substrate blends. Substrate components included a commercial greenhouse substrate (Fafard® 3B), pine bark (PB), STG, perlite and a composted product (PB:STG ; 50:50) referred to as TBC. Plant performance was evaluated for leaf chlorophyll content, growth indices, and dry weights. Substrate leachates were collected weekly to determine substrate chemical properties. PB:STG and TBC substrates produced similar or superior plants than Fafard® 3B. An additional greenhouse study determined the effect of pre-plant incorporated elemental sulfur on foliar chlorosis symptoms in petunia. Petunia x hybrida ‘Dreams Mix’ and Begonia x semporflorens-cultorum ‘Harmony Mix’ were grown for 10 weeks in a greenhouse. Plant performance was evaluated by comparing leaf chlorophyll content, visual quality, and dry weights. Petunias grown in a substrate containing up to 20% (by volume) STG were similar to those grown in substrates containing peat moss (PM). Incorporated elemental sulfur eliminated foliar chlorosis of petunia grown in STG substrates. In a container-plant production study, Lagerstroemia indica ‘Tuscarora’, Loropetalum chinense ‘Chang’s Ruby’, Nandina domestica ‘Fire Power’, and Rhododendron x ‘Micrantha Pink’ were grown in five substrate blends containing various PB:STG ratios. Leaf chlorophyll content and growth indices were used to determine plant performance. Substrate leachates were collected every four weeks in order to monitor pH and electrical conductivity. Crapemyrtle, loropetalum, nandina, and azalea, grown in substrates containing up to 50% (by volume) STG, had similar or greater growth than those grown in 100% PB. An additional container-plant production study evaluated Zantadeschia hybrids ‘Elliottiana’ and Hosta hybrids ‘T-Rex’ and ‘Wide Brim’ were grown in five substrate blends containing various ratios of STG:PB. Plant performance was evaluated by comparing root quality and foliar weight. Calla lily and hosta grown in substrates containing up to 50% (by volume) STG were similar to those grown in 100% PB.