They like fairly alkaline soil (idea pH 7.9 for black truffles). There are several kinds of truffles so you'll want to get a type that's adapted for your climate. For example, where I'm at the French Perigord / Black truffle matures after things are getting pretty frozen over, and the Burgundy truffle was recommended for my area. You want to plant them away from indigenous trees so the mycorrhizae from the locals don't come over and out-compete the truffle mycorrhizae.

I worked with Charles LeFevre at New World Truffieres to innoculate some Burr Oak acorns/seedlings. While the trees took quite well to the truffles, I thought my house would have been built long ago but alas my trees are still in pots (look nice though) and they're still too young to expect crops anywas.

Here is a link that might be useful: New World Truffieres

I bought 4 truffle-innoculated hazelnut trees from Charles Lefevre at New World Truffieres and planted them here on Chehalem Mountain outside Portland, Oregon. The trees are growing fine (about 2.5 feet tall), but plan to give the truffles several years to (hopefully) spread. Charles is very helpful via email.

I'm bumping this up because I gifted 5 Hazelnut trees to a relative in Santa Cruz CA (same climate as Oregon and lots of wooded areas where mushrooms abound), and I was wondering where do you get the spores? for the truffles and how do you innoculate?

Do you just purchase fresh truffles and plant them at the base of the hazelnut tree??

Truffles are entirely outrageously expensive, and I'd love to taste one, but if I must buy some, I'd like her to turn them into several more at the base of her Hazelnuts!