The method NuskeAlbert
provides a very simple method which is inspired by
standard climatological procedures but employs a 7 day moving average and
a 5 °C threshold (cf. Walther and Linderholm 2006).
Calculations
2 criteria: temperature & short day criterion
References
Walther, A. and Linderholm, H. W. (2006) A comparison of growing season indices for the Greater Baltic Area. International Journal of Biometeorology, 51(2), 107--118. doi:10.1007/s00484-006-0048-5 .