Over the weekend I was at our county fairgrounds for a 4-H function. Our fairgrounds is the best place I've found to forage wild onions and plantain; it grows so much earlier than at my house in the hills. You know what I did while I was waiting for the rest of my group to arrive, don't you?
I picked a bunch of plantain and stuck it in a plastic bag that was in the car. Leaving the bag in the car during the day helped to wilt the leaves. I brought it in the house when I got home and let the leaves "rest" in a towel overnight to absorb more moisture.
Next morning I tore the leaves and put them in a Mason jar, covering them with olive oil.
If you want to infuse oils, at this point you have two choices. You can set the jar in a sunny windowsill, gently shaking it daily, and wait 2 or more weeks, or you can put the plants and oil in a crockpot on LOW for a much shorter process. I've done both, but since I wasn't feeling well I put the jar in the windowsill until yesterday morning.
I transferred the contents of the jar to my little slow cooker and set it on WARM. Several hours later I strained the plant material from the oil and squeezed it to get every drop of the goodness.
I use infused oils in my soapmaking, and to make salves for my family and our horses and goats. Most years I triple-infuse the oil with chickweed, plantain and yarrow. The first step is to infuse olive oil with chickweed, then I strain out the plant material and add plantain to the oil. When that's finished, I strain out the plantain and add yarrow leaves and flowers to the same oil and let it infuse again. Because these plants aren't ready at the same time, I refrigerate the oil while waiting for the next herb to be "ready".
The yarrow is growing in plenty already. Our mild winter, warm spring, and plentiful rain means a very green landscape.