Crop Productivity and Morphology of Petunia and Geranium in Response to Low Night Temperature

Abstract

Seedlings of Petunia hybrida ‘Snow Cloud’ and Pelargonium × hortorum ‘Red Elite’ and ‘Cardinal Orbit’ were grown to anthesis at day air temperatures of 27° ± 3°C (9 hr) and either 7° ± 3° or 18° ± 3° night air temperatures (15 hr). Petunia crop productivity (CP, grams of dry matter produced per square meter of crop) and crop productivity efficiency (CPE, percentage of photosynthetic photon flux incident on the crop stored in the form of crop dry matter) were the same at both temperature regimes from canopy closure to anthesis, but anthesis was delayed 10 days at 7°. Petunias grown at 7° had four more basal branches and were only one-third the height of petunias grown at 18° (12 vs. 37 cm). CP and CPE were 20% lower for geraniums grown at 7° compared to CP and CPE for geraniums grown at 18°. The geraniums grown at 7° flowered 3 weeks later, were more compact, and were 16 to 19 cm shorter than geraniums grown at 18°.