Nutrition and effect of B-nine on zinnia grown as a winter pot plant : a dissertation submitted in partial fulfilment of the requirements for the Post Graduate Diploma in Horticultural Science in the University of Canterbury

Abstract

The traditional choices of midwinter-flowering pot plants in New Zealand have been chrysanthemum and poinsettia both with well established nutritional and photoperiodic regimes capable of producing consistently high quality plants. Such plants offer colour, tolerance to stress(low light, low humidity,etc.), as well as having the added bonus of being 'perennial'.

Criteria for selection of plants for year-round production are based on market demands and production considerations, acceptable species having showy and long-lasting floral display and/or attractive foliage,few insect and disease problems, and provide a satisfactory indoor pot plant for several weeks (Stefanis and Gortzig, 1979).

Zinnia elegans would appear to offer advantages of a long-lasting bloom in a range of colours not available from other plants in winter. As a rapidly growing and quickly-flowering annual it may have potential as a glasshouse plant although it may be anticipated that the high light and high temperatures combined with low humidity requirements may make it an expensive and more difficult crop,despite its short time in protected cultivation. Zinnia linnearis appeared to have potential for such production if low winter light levels could be enhanced and height controlled (Holcomb, 1982). Two zinnia cultivars (Dasher Scarlet, Small World Cherry) were flowered in eight to ten weeks as autumn pot plants when soil heat (24°C) was applied and had more flowers than plants grown 'cold'.

Information on the nutritional requirements of the plant are, however, scarce, especially with respect to quality characteristics. The present study was undertaken in order to add detail to this knowledge and to ascertain the value of growth retardants to control plant-height of tall growing varieties while maintaining flower size. However it is not necessarily expected that optimal nutrition alone can produce quality pot plants. If specifications approximating the 'golden mean' of 1.62:1(height: diameter) are to be achieved the use of growth retardants to control the proportions may be necessary.