so true! I got some freeze dried white widow from a friend, tasty but no moisture left to vaporize, unsatisfying result unless mixed with something else
You can use a hydrostone to add moisture to the herb. It works surprisingly well. The only issue is it will not last long, as in a few days the herb will go back to being dry. But for rehydrating the last small part of a batch before consumption, it does the job perfectly.
In case I do not have a hydrostone around, my "ghetto" solution is to load the stem and then drop a few drops of water in there. Just a few drops. It adds enough moisture to protect the plant while vaping and make the vapor more smooth. Not as good as with the hydrostone, because the moisture is outside the plant, but it produces a noticeable improvement.