Collection:
Dogbane lives in a variety of habitats and once you learn to identify it you will find it all over the place. It is best collected November to March.
Stinging nettle is a floodplain resident. It should be collected after the first frost and before much rain falls on it. This does two things. First, it lets the plant go to seed and second, it wilts some of the stinging trichomes that cause our skin to itch so terribly. You can touch the stalks and leaves with the palm of your hand with no ill effects. However, if those same plant parts touch the back of your hand or your arm you will itch for 20 minutes. Trichomes convey an acid that irritates the skin. Palm skin is too thick for the trichome to penetrate and cause stinging. Any doubts? Then wear gloves. In Missouri that time frame gives me about 2-3 months to collect the stalks before they begin to decline due to rotting. Be sure to remove the leaves before bundling.
Milkweeds should be collected in autumn. Make sure they are dry.
Use a pocket knife for all of these plants or some hand trimmers to cut your stalks. Bring a short hank of rope to bind your “bundle of switches” when you are ready to move on.
Store in a dry location for a few weeks to ensure they are completely dry.
Ethics: All three plants are perennial and have the active growing part of the plant near the base of the plant. Thus, last year’s stalks will simply rot in place. So you can collect 100% of the stalks after the growing season, without damaging the plant. However, I find that some insects do bore into old dogbane stalks. This encourages me to leave a third of the stalks where they stand in any location to ensure whatever it is doing the boring, can complete its life cycle. We are not the only ones who can use these plants!