The yellow herbs of summer: Elecampane.
Very good for slimy coughs.
Dig the root in fall (when they're rather sweet) or in summer (when they're quite bitter). I've seen a stand of garden escapees [*] once in the wild in southern Finland: it's mostly a garden plant, over here. A proud 2-3 m (6-9') tall yellow-flowering plant - unlike other tallish plants, this one won't fall over in the garden.
Wash the roots (don't bother trying to get the skin off - just get rid of small stones, earthworms and dirt), slice into 5 mm (⅕") coins (hah! a 4-5 year old plant has a root the size of a head ... coins indeed. Get out your sharpest breadknife and just start slicing things where you can, is a better idea), and dry the root bits, or make them into a syrup. The taste is interesting: at first bite it's nicely aromatic (wonder why this root isn't in general use?), about half a minute later it gets very bitter (summer root, that is) (ah, now I know why it's not in general use ...), and perhaps half a minute later your tastebuds go numb for 30-60 minutes (wooo, lovely root!).
Syrup: You get a very good cough syrup from elecampane root. It's one of the most effective herbs (or syrups) I know of for slimy coughs, and it's even better if there's an element of digestive troubles behind the cough (your protein digestion is wonky -> your immune system doesn't work properly (the immune system is all proteins) -> you have a queue of respiratory troubles, and they're all waiting for their turn, waiting for the previous lung grunge to clear out so the next one can hit you (if your lungs are the weakest spot in your body, that is)).
It's easy to make a syrup: put a handful or two of roots into a pot, add about 5 dl (1 pint) of water, bring to a boil. Let boil for 20 minutes or so, strain, pour 2 dl (½ pint) back into your pot, and add 450 g (1 lb) sugar. Warm (don't boil) and stir until the sugar has melted. Pour into a glass jar, close lid, add label.
Take 1 teaspoon of the syrup when needed.
[*] Can you see them, too, yelling and jumping over all the fences? "Wheee, we're free, free, freeee ... !"