The only time weed is unsafe to smoke is when it has mold on it. Sometimes it's hard or impossible to know unless your spoiled and live near a dispensary that sells lab tested cannabis.
You should be just fine leaving your herb in the grinder for a few days. After that it will get harsh and dry. As others have said, to restore your herb if/ when it gets dry and harsh you can use an orange peel, moist paper towel, amazon has these little metal pucks with small holes and has a porous material inside. Moisture Pouch Buttons for Fresh Tobacco
https://www.amazon.com/dp/B00326GR9W/ref=cm_sw_r_cp_api_XbKzybK5AQXHS
Happy trails!
I can't remember the exact number, but the ideal humidity for pipe tobacco is less than cigars. Mason jars are your best bet for storing pipe tobacco long-term, and the airtight seal even means the tobacco will age over time. You also want to be careful of cross-contamination since pipe tobacco can have a range of strong aromas.
I like to use button humidifiers when my pipe tobacco gets dry (like these: https://smile.amazon.com/Moisture-Pouch-Buttons-Fresh-Tobacco/dp/B00326GR9W/ref=sr_1_1_a_it?ie=UTF8&qid=1489516134&sr=8-1&keywords=button+humidifier). Just dip them in distilled water, pat dry, and throw them in the jar on top of the tobacco for a couple days.
My grandfather used the skin of apples or potatos. But you can get tobacco moisturizers like this one
I picked up some of these. Used one in an open can that was beginning to dry out. Popped it in the fridge with one in the can. Works great. http://www.amazon.com/Moisture-Pouch-Buttons-Fresh-Tobacco/dp/B00326GR9W/ref=sr_1_35?ie=UTF8&qid=1426185497&sr=8-35&keywords=mudjug
https://www.amazon.com/Moisture-Pouch-Buttons-Tobacco-Discs/dp/B00326GR9W
So something like that? We talking days, weeks, months?
https://www.amazon.com/Moisture-Pouch-Buttons-Tobacco-Discs/dp/B00326GR9W use them for my bulk tobacco, they help some.
Reminds me of a humidor discs used to keep tobacco fresh.
Try these humidifier buttons You just soak it in distilled water and you should he good to go
http://www.amazon.com/Moisture-Pouch-Buttons-Fresh-Tobacco/dp/B00326GR9W
Buy those and you'll be sorted. Never have dry snus again.
Anyone tried the humidifier discs that's usually used for pipe tobacco?