You can only pickle walnuts when the shells are soft - you need to pick them in about June, so make a note on your calendar for next year. You prick them a couple of times, cover in a thick layer of salt for 3 days, wash off salt quickly, cover with hot spiced vinegar & put in jars with seals or waxed paper between lid & jar, ready to eat in 3 to 4 months. Dead easy and so much cheaper than buying pickled walnuts - in the shops they are £2 or £3 for a small jar!