Update on my sorbus seed experiment: two or three seeds have germinated out of the 14 in each pot by mid-March. I was going to photograph the seedlings, but a slug had them for breakfast today! I will try to be faster with the camera if any more germinate this spring.
It would appear that soaking, whether in water, lemon juice or vinegar, makes little difference to germination. Just as many seedlings germinated in the pot where the fruit pulp was merely removed but not soaked.
