GROWTH OF BEDDING PLANTS AND POINSETTIAS IN MINERAL WOOL AND MINERAL WOOL PEAT SUBSTRATES

Studies were conducted to ascertain the suitability of mineral wool (M W), either alone or in combination with sphagnum peat moss, as a subst rate for potted greenhouse plants. Two types of hydrophyllic mineral w ools, cleaned mineral wool (CMW) and uncleaned mineral wool (UMW), wer e used. Unamended CMW had a low bulk density, excellent water holding capacity, good aeration, but a high pH. Once peat moss was added to th e CMW, bulk density remained low, water holding capacity remained good , and the pH dropped to a more suitable level. Unamended UMW had a hig h bulk density, good water holding capacity, poor aeration, and a high pH. Once peat moss was added to UMW, bulk density decreased, water ho lding capacity remained good, aeration increased, and the pH decreased to a more optimal level. CMW and UMW, were used unamended, as well as amended with 25%, 50%, and 75% pear moss. Two bedding plants, Impatie ns walleriana 'Dazzler Violet' and Begonia semperflorens 'Whiskey' wer e grown for six and nine weeks respectively, and Euphorbia pulcherrima 'Glory' was grown for 20 weeks, in nine different substrates. Plants grown in unamended CMW and UMW were generally smaller in size and lowe r in fresh weight than plants grown in 50% MW/50% peat moss. The plant s grown in MW with either 25% or 75% peat moss were similar in size an d weight to plants grown in 50% MW/50% peat moss. Plant tissue analysi s showed that generally plants were receiving adequate nutrition.