Scheduling crops of "containerized" roses

Two experiments between 1995 and 1997 studied the effects on bud development through to flowering of lifting bare-root rose plants of cv. Warm Wishes from October to December and potting them immediately or at intervals from February to July after cold storage. In both experiments the times of four key morphological stages, bud burst, first expanded leaf, flower bud and bud showing colour, were recorded on terminal shoots. There were no significant effects of lifting date on the time from potting to any morphological stage and in the first experiment the most appropriate storage temperature was 0 degrees C. The major effect on time to all four morphological stages was the time of potting, with later potting resulting in progressively shorter intervals to each stage. For crops potted in the year in which they flowered the most appropriate of the environmental scales considered for describing the period from potting to buds showing colour was day-degrees >4 degrees C. On average, crops required 772 day-degrees >4 degrees C from potting to bud showing colour and 543 day-degrees >4 degrees C from the first expanded leaf to the same stage. Using meteorological data from 1989-1998, simulations of the time to buds showing colour were run for crops potted at the beginning of each month from February to July. These enabled effects of yearly variations in temperature on predicted marketing dates to be estimated. They show that, on average, buds were predicted to show colour between 17 June (February potting) and 28 August (July potting) and that over the ten years the range of predicted flowering dates was 34, 23, 17, 18, 13 and 17 d from potting at monthly intervals from 1 February to 1 July respectively. This model provides a framework for scheduling potting dates to extend the season and maintain continuity of supply of plants at the optimum stage for marketing.