Research Matters - Scheduling growth in the greenhouse

The ability to schedule the growth and flowering of greenhouse crops is important to growers. In the experiments reported here, 18 different bedding plants were raised from seed.

When ready, they were transplanted from plugs into plastic containers (480ml) of a soil-less medium and were grown in growth chambers. The environments consisted of a standard irradiance and constant temperatures of 5, 7.5, 10, 15, 25 and 30 degC.

Flowering was defined slightly differently for each of the 18 species but the assessments of the time of flowering at each temperature were then converted into rates.

The relationships between the rate of flowering and mean day temperature were described using an equation. This gave the minimum and maximum temperatures at which the rate of flowering was zero and optimal.

Such temperatures are given for most species and graphs of flowering rate against temperature are presented for all 18 species.

The optimum temperature for flowering rate of Dahlia 'Figaro Mix' was 19.1 degC, but it was higher for most other species. With Dianthus 'Super Parfait Raspberry' and Gazania 'Daybreak Bronze', the optimum was around 27-28 degC.

However, the optimum temperature for flowering may not necessarily be the best for growth or plant quality.

Dr Ken Cockshull, Associate Fellow, Warwick Crop Centre, University of Warwick.

Quantifying the Thermal Flowering Rates of Eighteen Species of Annual Bedding Plants by Blanchard and Runkle (2011).

Scientia Horticulturae 128 (1): 30-37. The contents of Scientia Horticulturae issues and abstracts of papers are provided at

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