Past Their Prime from Drying?

Another indicator is looking at the width of the cracks. If you can stick a dime in the biggest cracks, the wood is approaching the "too dry" phase, termed "fiber saturation point" where the free water in the wood cell is gone and now the bound water within the wood cell wall is drying up, physically changing the structure of the wood and it's ability to support good fungal growth. This occurs when the wood is approximately 20-30 percent moisture. You can take a moisture test by cutting a wafer of the wood, drying it and calculating the moisture content, or just looking and feeling the surface of the log end. It will feel very dry. Again the exact timeframe when this happens will vary based on where you live, log size, storage, etc. so, unfortunately, we cannot give the exact timeframe.

past-prime logs

Logs with severe cracking - this log is too dry for inoculation.

Other Factors to Consider...

While drying of logs is a huge factor in deciding the suitability of your logs, another thing to keep in mind is other native fungi moving into your logs before you inoculate them with your desired species. After cutting your logs it's helpful to store them on either a concrete slab, a pallet, or stringer logs to keep them slightly off the ground. Keeping your logs away from direct contact with forest floor will create a space barrier that will prevent native fungi from easily inhabiting the wood. Typically if you cut logs in the spring of the year, you will want to inoculate the logs within a month of harvest. If you live in the north where fungal activity is a little slower than you have a little bit longer, but if you live in the south you will want to inoculate the logs within a month of cut.