AbstractTemperature and daylength treatments have been used to investigate the apparent link between the potential for rapid leaf extension in spring and floral initiation and development in Lolium perenne (cv. Vigor). After growth at 5°C for 10 weeks (vernalization treatment) the leaves which developed at 15°C expanded significantly faster than non‐vernalized controls under both long and short days. Under long days floral development was initiated in vernalized plants but under short days it was not. Specific leaf area was higher in vernalized than non‐vernalized plants under long days.The photosynthetic capacity of leaves which developed on plants which had been previously vernalized and then grown at 15°C under long days was higher than non‐vernalized controls when expressed on a leaf area and dry weight basis, but not on the basis of chlorophyll content. Vernalization followed by short days resulted in a smaller and non‐significant increase in the photosynthetic capacity of leaves.Application of gibberellic acid (GA) as a spray to non‐vernalized plants did not affect floral development but did increase the rate of leaf extension. The application of GA did not affect specific leaf area or photosynthetic capacity expressed on a