Abstract: Based on the data of the field experiments in 2004-2006,the characteristics of the growth and development of the citron daylily(Hemerocallis citrina) under traditional growing pattern,and the hydrothermal effects and growth characteristics under the protected and field cultivation were compared.The results showed that the effect in increasing temperature and keeping soil moisture was significant by plastic mulching,while the growth period of the citron daylily advanced and grew better,but with relative lower yield.The excessive increase of the soil temperature in spring was effectively strained by the straw mulching,and the soil moisture evaporation was reduced.Consequently the picking period was extended with a relative high yield.It was concluded that the mulching during the overwintering period could reduce the non-effective consumption of the soil moisture in the non-growing periods,and reduce the influence of the spring drought on the growth of the citron daylily.The straw mulching was recommended as one of the low cost mulching techniques.

Key words: Protectd field, Protectd field, Citron daylily, Plastic mulching, Straw mulching