Hello,

Thank you for the question. Really you can use any wood with this kit, with the exception of pines and cedars because of the sap contained in those are not condusive to mycelium growth. We recommend hardwood for the following reasons. The sapwood is what the mushroom fungus feeds on during the life of the log. The sapwood is the portion of the log that surrounds the hartwood, that's the dark core which is located in the very center of a log, the bark surrounds that. In hardwoods the sapwood is very dense and takes the fugus longer to consume it. In soft woods the sapwood is less dense and the fungus consumes it more rapidly cutting the life of the log in some cases by 50%. Softwoods include elm, birtch, cottonwood, maple, etc. A premium harwood to use is oak.
For example lets say you use a hardwood log 12" long and 4" in diameter (by the way we give you enough spores in this kit to do a log this size if you want) Your general incubation time would be 2-3 months, and the life of your log would be 4-8 years.

If you did the same size log with a softwood your incubation time would be 1-2 months and the life of the log would be around 3-5 years.
Hope this helps.