Tropical Tree in Germany?

Unfortunately, I had two tests (each 3 seeds) no luck. One seedling had at least managed to appear at all, but was due to lack of solar heat (in December) just too weak, since even cajoling and a UV lamp has not helped;)
Stands on the package, you can put the seeds throughout the year, of which I would like to advise - see above. I'll try it now again in the spring.