Thought about growing them last year, but didn't go ahead. Here's the advice from one seller.....
"Supplied as wooden 'spawn plugs' - all you need to do is find some freshly cut logs, drill holes in them and push them in. Cropping commences after 4-10 months and continues 3-5 times a year for 3-5 years."
Another specifies hardwood logs and adds:
"Please note that these dowels are available all year, however the logs should be cut during the trees dormant season, between leaf fall in autumn and early spring, and it is recommended that the dowels are planted in the log no longer than 6 weeks after the log has been cut"
- so why do they supply them all year round?