Effects of Dense Planting on Yield and Growth of the Purple Asparagus Variety ‘Purple Passion’

Abstract

Purple asparagus is becoming popular among consumers in Japan because of its unique appearance, thickness, sweetness, tenderness of the spears, and quality of vitamins and minerals. The growing area for purple varieties such as ‘Purple Passion’ is spreading, particularly in cool regions of Japan. However, lower yields compared to those of major green varieties have been regarded as a serious problem. Therefore, some growers hesitate to cultivate the purple varieties. In order to improve the yield of ‘Purple Passion’, we investigated the effect of high density planting on mother fern cultivation between 1999 and 2005. The yield of plots with a normal planting of ‘Purple Passion’ was lower than that of ‘UC157’ which is a green asparagus variety cultured in Japan. However, the yield of ‘Purple Passion’ in the plot with dense planting showed yields as high as those with normal planting of ‘UC157’. The spear weight of ‘Purple Passion’ in all treatments was larger than that of ‘UC157’, although the number of harvested spears of ‘Purple Passion’ per unit area was decreased compared to that from a normal planting of ‘UC157’. This advantage might contribute to labor-saving. These findings suggest that ‘Purple Passion’ can achieve a sufficient yield when cultivated by dense planting. The aptitude for dense planting and its unique properties are key factors in achieving stable cultivation and promoting the consumption of purple varieties in Japan.