Apparently, it would work very well in tincture form. Here is a link to an ephedra tincture which is NOT the "official' (ephedra sinica) plant, but which they say works "as well". Not having asthma myself, I can't test that, but it would be worth trying while you're trying to get your own plants going of the official species.
http://www.terrafirmabotanicals.com...tm_medium=feed&utm_campaign=googleproductfeed
You should be able to make tincture or tea from fresh or dried leaves. For tincture, if using dry plant material, use a 80 or 100 proof vodka as the menstruum. For green leaves, use a minimum of 100 proof, and preferably 160 proof vodka (or dilute pure grain alcohol to 80%), to adjust for the water naturally in the plant material.
For dry herb, use 1:5 ratio herb to menstruum... 100 grams dried herb to 500 mls menstruum. For fresh herb, it's usually 1:2, or simply pack as much fresh herb as you can in a glass jar and pour the vodka over it.
Summerthyme