We evaluated the effects of pre-sowing treatments such as near-infrared (NIR) light sorting (for filled seeds) and fungicide cleansing on the germination rate of Cryptomeria japonica and Chamaecyparis obtusa seeds, which were stored dry for 18 months below freezing. After NIR light sorting, seed germination rates of both species were greatly increased; as for C. japonica, more than 90% of all collected seeds successfully germinated, the rate considered as the minimum requirements for containerized seedling production via single-seed sowing procedures. On the other hand, seeds of both species soaked in fungicide solution or water before sowing exhibited a tendency to germinate earlier than unsoaked controls. However, these cleansing treatments did not perfectly prevent seed deterioration due to mold breeding or putrefaction, and hence the effect was not significant at later than two weeks after sowing. It is expected that future development of methods for identifying stale seeds and/or for preventing sown seeds from deterioration will further contribute to improve production efficiency of afforestation tree seedlings.