[AlaninCarlisle]

Followed instructions on packet very precisely. Pressed into seeding compost, kept moist and in a heated propagator at 21C. After three weeks, nothing!

Is there a trick of the trade to germinate these, or should I just give them a couple of weeks more?

[Eblana]

I didn't sow mine until end of Feb last year and even then only got patchy germination.  Light levels possibly too low for them.