Germination is successful only when GA3 is used. See http://botanicallyinclined.org/fridays-seeds-with-the-ga3-seeds-treatment
Give sown seeds several weeks @ 20°C to imbibe water (perhaps even germinate!), then expose to fluctuating outdoor winter temperatures including freezing for 3 months. Gradually increase light and temperature in spring. See https://www.youtube.com/watch?v=SO_KKbGYTEM