Mix formulation and preparation

Abstract

A brief historical review of the development of loamless mixes shows the difficulty of attempting to establish a date for their first introduction or general acceptance into horticulture. As with many horticultural practices, evolution has occurred over a long period. Peat, leafmould and pine needles have been used for growing azaleas by many generations of gardeners, and experiments made at Versailles in 1892 on the nutrition of azaleas in these media are described by Watson (1913). Laurie (1931) in Ohio, usa, experimented in the late 1920s and early 1930s on the use of peat—sand mixtures for growing a range of plants, but no further development of this concept appears to have occurred for the next 20 years. In the 1950s, American workers at Michigan (Asen & Wildon 1953) and in California (Baker 1957) revived the interest in the use of peat and sand by obtaining favourable results in comparison with plants grown in traditional mixes based on mineral soils. In Europe, Penningsfeld, working in Bavaria, initiated work on the use of pure peat as a medium (Penningsfeld 1962), and Puustjärvi (1969), working in Finland, developed a system of growing in peat known as ‘basin culture’. With this system, vegetable and ornamental crops are grown in peat, isolated from the glasshouse border soil by a sheet of polythene. Several attempts have been made to include clay, in either powdered or granular form, into mixes made from peat and sand. Fruhstorfer (1952) used a 1:1 mixture of granulated clay and peat to formulate his ‘Einheitserde’ compost. Dempster (1958) recommended 10% by volume of clay to 40% peat and 50% sand, and Dänhardt & Kühle (1959) reported a progressive increase in growth as the amount of clay mixed with the peat was decreased to 10%; the inferior result when growing plants entirely in peat was attributed to the very low pH in the absence of some clay. Difficulties over supply and quality control have restricted the use of clay in mixes; early unpublished work by the author showed that adverse effects on pH, microelement availability and forms of nitrogen could occur if the clay contained more than a very small amount of calcium carbonate.