BARK-AMENDED AND PEAT-AMENDED SPENT MUSHROOM COMPOST FOR CONTAINERIZED CULTURE OF SHRUBS

Four deciduous ornamental shrubs ['Coral Beauty' cotoneaster (Cotoneas ter dammeri C.K. Schneid); Tartarian dogwood (Cornus alba L.); 'Lynwoo d' forsythia (Forsythia xintermedia Zab.); 'Variegata' weigela (Weigel a florida Bunge A.D.C.)] were grown in trickle-fertigated containers. There were eight media consisting of 25% or 50% sphagnum peat or compo sted pine bark, 25% sand, and the remainder one of two sources of spen t mushroom compost; four media with 50% peat or bark mixed with 50% sp ent mushroom compost; and a control medium of 100% pine bark. Initiall y, higher than desirable salt levels in all compost-amended media were leached quickly (within 2 weeks of planting) and not detrimental to t he species tested. Unlike cotoneaster, which showed no difference in g rowth (shoot dry weight) due to medium, dogwood, forsythia, and weigel a grew significantly better in all compost-amended media than in the c ontrol. Growth of these three species was 20% greater-in peat-based th an in bark-based, compost-amended media. Dogwood and forsythia grew sl ightly more (+8%) with spent mushroom compost based primarily on straw -bedded horse manure than with one based on a blend of straw-bedded ho rse manure, wheat straw, and hay. The addition of sand (25%) to a mixt ure of 50% peat or bark and 25% spent compost produced a medium with m inimal compaction.