Our garden has a 15 year old Japanese Walnut tree. We live in Denmark. I harvested the nuts back in October and kept them in a bowl. There are still about 10 left. The apartament is quite warm, 27-29C on average. Now I'm reading about walnut propagation and I would like to try to germinate the nuts but the guides ask for fresh nuts. Is it too late already and I should wait til next year's harvest?
Go for it. You might not have as good of germination rates as if the walnuts had been kept in a cool environment, but in a "worst case scenario" you will only be out 10 walnuts and a few minutes of your time. At the very least, you'll gain experience for next year.
I had some black walnuts germinate a year and a half after harvest. They had mostly been in moist soil in the fridge, then some ended up in pots outside after a year, some ended up in a bag for several months and weren't kept particularly moist. I thought, eh, toss them in a pot and see what happens, and several germinated. So long as the embryo doesn't completely desiccate nuts can stay viable for some years. Give it a try!
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