I had these weeds growing in my yard, they reminded me of Japanese Indigo and I thought maybe I can do something with them:
As a Girl Scout, I always won the plant identification contest, I enjoyed poring through books to find the match. So I used Google and identified these as Polygonum Persicaria, in English smartweed (among other names: Redshank, Lady's thumb, Heartweed), in Icelandic flóajurt, in Norwegian hønsegras. (It's really interesting to me how sometimes weeds have so many names, this one even has two different Latin names, the other one is Persicaria maculata.)
Lots of sources said you could dye with these, and it would be yellow, including a Norwegian site given me by someone on the Natural Dyeing list which said the Vikings used this. (Too bad it's not THAT closely related to Indigo!) I also found in one of my books that it suggests drying them and then making a solution and letting it ferment... so I have dried some of the plants (240g) that I picked to see how that goes. But these ones I tried fresh. First I made the dye solution of 288g of fresh plants (stems, leaves, and flowers), by bringing them up to a simmer and simmering around 2 hours.
Then I tried two things. I was going for variegated yarn, so I put 1 Tbsp baking soda in one jar, and left one alone. I stuck one end of my skein (86g) in one jar, the other end in the other jar, and put the jars into the dye bath. I didn't get so vibrant a colour, because the yarn was crowded in the jars. I would love to hear a better solution for this. Anyway, the baking soda end came out more golden-brownish, and the regular end came out more greenish, and here's my swatch:
I then tried a skein (78g) just straight into the dye bath, like normal:
It's definitely a deeper yellow than the Lily of the Valley one.
All yarn here is mordanted with alum (I mordanted while dyeing). Both skeins I cooked around 2 hours, I believe, and let soak in the bath overnight. I'll post again when I try the dried leaves.