Trends in Rooting Media in Dutch Horticulture during the Period 2001-2005: the New Growing Media Project

An overview of the developments in the area and volume of substrates used for horticultural rooting media in Holland in the period 2001 to 2005 is given. The overview is followed by a discussion of some trends in society and technology including the interest of public and society in a possible substitution of peat, an increase in the use of locally produced renewable carbon based substrates and an increase in nutrient recirculation for soil grown crops. In reaction to growing public concern about peat harvesting for horticultural purposes in parts of Europe, Dutch growers, researchers, potting soil producers, an auction and traders initiated in 2003 a research program named the New Growing Media Project. The aim was: To assess the technical and economical potential of peat alternatives. Develop experience and knowledge of growing on alternative mixtures. During 2004 and 2005, fifteen growers cultivated green and flowering container plants on alternative mixes. The 2004 season was used to test larger numbers of potting soils with relatively small numbers of plants. The 2005 season was used to test the most promising potting soils with larger numbers of plants. The results showed that for Hedera and Schefflera, the ultimate alternative mix was superior to the commercial standard used. For five species, Anthurium, Chrysanthemum, Gerbera, Spathiphyllum and Castanospermum, the alternative mix proved equal to the commercial standard. For eight species, Azalea, Guzmania, Poinsettia, Rosa, Saintpaulia, Adiantum, Crassula and Ficus, results were poorer than on the standard medium. The growers however, felt confident the alternative mixes could do better if the growing system, often the irrigation frequency, could be adapted to the experimental growing medium. Begonia gave poorer results with the new mix. The percentage peat used in the mixes was reduced from 77% on average in the commercial standard mixes to 30% on average in the new mixes. The most popular alternatives were coir products which increased from 17 to 40%. Other alternatives used were various barks, rice hulls, perlite, wood fiber, composts, and rockwool granulate. Those alternatives were used in mixtures from 5 to 30%. General conclusions include a growing interest in locally produced composts, granulates and fibers and for materials with properties such as a high initial air content combined with an improved rewetting rate.