Oops. I meant to type freeze. It's sitting in my freezer right now. All this henna stuff is very word of mouth on the internet, but every generally seems to be right. It would be nice if there seems to be more research.
So far my new henna color (done with henna that was frozen for 2 months) seems very similar to the old one. I did want a richer, darker color though. It's very hard for me to tell, but it seems similar to me.
After this I am planning on just doing root touch ups, so hopefully my head will stay at this darkness of red.