Relationship of Soluble Salts Content in MSW Compost Media and Rooting of Evergreen Cuttings

Municipal solid waste (MSW) compost media with various levels of soluble salts were used for rooting stem cuttings of nine evergreen landscape shrubs: Buxus sempervirens L. ‘Green Gem’; Juniperus chinensis L. ‘Hetzii; J. chinensis ‘Mint Julep’; J. chinensis ‘Pfitzeriana Aurea’; J. horizontalis Moench ‘Bar Harbor’; J. horizontalis ‘Blue Chip’; J. sabina L. ‘Blue Danube’; Taxus x media Rehd. ‘Densiformis’; and Thuja occidentalis L. Rooting occurred during the winter in greenhouse compartments supplied with bottom-heated benches filled with 100% sphagnum peat or 100% perlite, or peat or perlite mixed with 15, 30, 45, 60 or 75% by volume of MSW compost. The electrical conductivity (salt) levels were similar in MSW compost with peat or with perlite (range, 0.05-0.60 dS·m−1 with 0-75% compost) and positively correlated with levels of MSW (r = 0.88, P≤0.001). With few exceptions, cuttings rooted similarly in MSW with peat or perlite. Depending on taxa, increasing salt levels had various degrees of diminutive, neutral, and enhancing effect on rooting response, expressed in terms of percent rooting, root number per cutting, and root length (longest root per cutting). Four taxa (J. horizontalis ‘Bar Harbor’ and ‘Blue Chip’, J. sabina ‘Blue Danube’, and T. occidentalis) were tolerant of the salt levels tested (positively influenced or unaffected). The other five taxa were intolerant (adversely affected).