Effects of soil temperature on head development of Cos lettuce

Cos lettuce plants (Lactuca sativa L. cultivar ‘Romana’) of 2 ages were grown for 30 days with soil temperatures of 12°, 20°, 28° or 36°C. The highest temperature caused poor growth and heading and quick head disintegration. Best heading occurred mainly at lower temperature, although the lowest one sometimes delayed growth. Higher temperatures did not enhance real bolting, as growth of the inner stem was accelerated.