I haven't studied Tractate Kilayim. I know you can't plant grapes with wheat. What about, say: Jazz apple = Royal Gala apple X Braeburn apple ? Nectarine = Peach X Plum ? Nectaplum = Nectarine X ...
Where did the idea of doing a Seder on Tu b'Shvat come from? Why a Seder, not just the eating of fruit? Why do we call it a Seder if there is no formalized way of doing it?
What is the earliest source for the custom of dipping an apple in honey on Rosh Hashana? (It is found in the Tur (Siman 683), the Abudraham (quoted by the Rama there) - believed to be a student of ...