A Novel Method of Supplying Nutrients Permits Predictable Shoot Growth and Root: Shoot Ratios of Pre-transplant Bedding Plants

†Background and Aims Growth of bedding plants, in small peat plugs, relies on nutrients in the irrigation solution. The object of the study was to find a way of modifying the nutrient supply so that good-quality seedlings can be grown rapidly and yet have the high root: shoot ratios essential for efficient transplanting. †Methods A new procedure was devised in which the concentrations of nutrients in the irrigation solution were modified during growth according to changing plant demand, instead of maintaining the same concentrations throughout growth. The new procedure depends on published algorithms for the dependence of growth rate and optimal plant nutrient concentrations on shoot dry weight Ws (g m 22), and on measuring evapotranspiration rates and shoot dry weights at weekly intervals. Pansy, Viola tricola ‘Universal plus yellow ’ and petunia, Petunia hybrida ‘Multiflora light salmon vein ’ were grown in four independent experiments with the expected optimum nutrient concentration and fractions of the optimum. Root and shoot weights were measured during growth. †Key Results For each level of nutrient supply Ws increased with time (t) in days, according to the equation DWs/Dt K2Ws/(100 þWs) in which the growth rate coefficient (K2) remained approximately constant throughout growth. The value of K2 for the optimum treatment was defined by incoming radiation and temperature. The value of K2 for each sub-optimum treatment relative to that for the optimum treatment was logarithmically related to th