Use repeated cycles of 4°C, then 20°C for 3 months each. Germination is very prolonged.
germination unlikely after dry storage > 6 months; leaf may not emerge for 2 cycles after radicle.
Research by Jeffery and Carol Baskin demonstrated "Freshly-matured seeds of ... Jeffersonia diphylla .....have underdeveloped (ca. 0.6 mm in length) embryos and exhibit deep, simple morphophysiological dormancy (MPD). For rapid growth of the embryos at October (20°/10° C) and November (15°/6° C) temperatures in October and November, seeds must first be exposed to high (30°/15°C) summer temperatures. If embryo growth is not completed in autumn, it continues during winter. However, even after 10-12 weeks at summer temperatures, embryos grew very little at 5°C, unless growth already had begun at autumn temperatures. After embryo growth has been completed, or after it has been initiated, seeds require cold stratification (5°C) to overcome dormancy. Embryos must attain a minimum length of about 1 mm before seed dormancy can be broken by cold stratification. Gibberellic acid increased the rate of embryo growth in seeds kept at 20°C, but only 1-9% of them germinated. Thus, GA substitutes for warm but not cold stratification. High summer temperatures, as well as the traditionally-used autumn and winter temperatures, should be used in germinating seeds with deep, simple MPD."
Sow @ 20°C for 6 weeks, then place @ 4°C for 6 weeks, then slowly raise temperature to 10°C for 6 weeks. If there is no germination, repeat the cycle. This mimics fall sowing outdoors for spring germination.
sow fresh or soak old seed; prechill 4 weeks or place outdoors over winter and bring indoors once germinated to avoid temperature shock; transplant at 4 leaves