MEASUREMENT OF FROST HARDINESS IN TWO-YEAR-OLD DOUGLAS FIR SEEDLINGS

Abstract

Seasonal changes in electrical conductivity, impedance, cambial activity and apical growth were investigated during three winters in relation to frost hardiness of two-year-old Douglas fir seedlings. Conductivity of stem diffusate and stem impedance, following freezing at −9.5 °C for 16 hours, were well correlated with hardiness of potted plants to the same treatment. Cessation and commencement of cambial activity coincided quite closely with development and loss of hardiness, but terminal bud formation was a poor indicator of hardiness. Seasonal changes in conductivity were associated with concentration changes of potassium in the diffusate. Hardiness of both nonhardy and hardy seedlings was unchanged by storage at 0–2 °C in plastic-lined bags in darkness.