Cold hardiness of Phellodendron sachalinense Friedr. Schmidt seedlings increases with age

Seedlings of several landscape tree species frequently experience cold inju ry at temperatures that are noninjurious to older specimens of the same spe cies. However, there are few published reports quantifying age-related diff erences in hardiness. In this study, the stem cold hardiness of a mature, 3 5-year-old female Sakhalin corktree was compared with that of half-sib seed ling progeny of different ages. Ten-, 22-, and 34-month-old seedlings were hardy to -4 degrees C on 9 Oct., while the 35-year-old parent withstood -12 degrees C. Ten-month-old seedlings exhibited no further increase in hardin ess on 26 Oct., whereas the 34-month-old. seedlings and the mature parent w ere hardy to -16 degrees C. The 22-month-old seedlings were intermediate in hardiness on this date. The 10- and 22-month-old seedlings had died back t o the snowline by late January, but the 34-month-old seedlings and the matu re tree were uninjured, The corktree seedlings did not attain midwinter har diness levels comparable to the adult tree until the winter following their fourth season of growth. The absence of flower buds on cold-tolerant 4- an d 5-year-old seedlings suggests that physiological maturation is not a prer equisite for full expression of the cold acclimation capability of this spe cies.