Yes. Most people who use herbs magically use them in dried form. Now, there is a limit - you wouldn't want to use very old dried plants that have lost most of their essence.
Plants aren't just a tool to focus your intent or to decorate your altar space - they have a magical ressonance all their own. Sometimes a good herbal mixture will do most of the work for you - no belief or extra work on your part needed.
Basically, i treat my magical herbs the same way as my cooking herbs. If they don't smell, if they don't have "life," energy, charisma, i put them in the compost pile. Depending on the herb, whether it's a dried root, flower, or leaf, you usually have a year or two before they start to go downhill - and of course you have to store them in the all-important air-tight "dark, dry space."
Hmm, I see, thank you very much for the information. I actually made a homemade bag out of a nice black cloth and a cheap pendent which is where i store the leaves, the only air-tight container I have is a bottle (Which i'm saving to make some holy water out of)
well medicinal you should only keepy dried herbs for one year, becuase they will less their potency. but magickaly you can use them until they lose their smell or if you dont think they should be used.