The walnut tree was introduced from Asia about 500 years ago. It does not spread very successfully when left to its own devices but they are not uncommon in woods and parkland, and indeed in people's gardens. The nuts do not always ripen fully in our climate, and it is best to allow them the benefit of any autumn sunshine and pick them as late as possible: late October or even early November. Ideally the fruit surrounding the nut should be split and the shell of the nut showing through. Peel away this fleshy case and, if you are not ready to use the walnuts straight away, or want to keep them for your nut bowl, leave them to dry in an airing cupboard for 24 hours, then transfer them to a cool, dry place. This should ensure they don't go mouldy. Wild walnuts can be used instead of the imported cultivated kind in any recipe, but because they have a particularly strong flavour I prefer to use them in savoury ones. They make a great pesto, in place of pine nuts.