Difficulties were observed in the leafing of mature birch, alder, and willow species in southern Finland in the spring 1989, especially at lush growing sites. The suspected reason was freezing of the buds in the preceding autumn caused by disturbed bud dormancy. The hypothesis was tested experimentally with 1-year-oldBetulapendulaRoth seedlings, investigating the effects of partial defoliation, nitrogen nutrition, and temperature. Defoliation clearly weakened both the growth and overwintering of the seedlings, altered the carbohydrate relations in their roots, and markedly delayed leafing in the spring. The earlier in the summer the defoliation was performed, the more conspicuous were its effects, which were also emphasized by the fertilization. A short greenhouse treatment in autumn had no significant effect, however, and it is thought that the partial death of the defoliated top shoots may have been caused by frost drying. The main reason for the late leafing seems to be the delayed development of the buds as a consequence of early defoliation. On the other hand, the growth-promoting effect of nitrogen fertilization and the premature branching of the buds evidently disturbed the carbohydrate balance in the roots and thus the development of the whole seedlings.