Those are dandelion roots. And I'm sure you know how much fun digging those up can be. It took me ages to dig up a reasonable amount but curiosity made it worthwhile.
I started with a 50g skein of undyed 4-ply wool, mordanted with alum and cream of tartar.
For my dandelion root experiment I used approximately 60g of chopped dandelion root, which I simmered in water for about an hour. Then I added the wool, dry - I should probably wet it first but I always forget. I didn't bother removing the bits of root, deciding that it'd probably be easy enough to pick the bits out of the wool.
I simmered the wool gently for an hour then had a look at the resulting beige and decided it was too boring and I ddn't want another beige. So I added fresh dandelion leaves, unweighed but a big handful which I simmered for another hour then had another look. Still beige though a little more yellowy, so I turned the heat off and let it steep overnight.
The next day I decided it was still just too boring (there's subtle and there's plain dull) so I drained the dandelion liquor and picked out the bits of root and leaf.
And it was time to bring out the big guns in the form of brown onion skins. I'd been saving these all winter and had loads so stewed up a bagful for an hour.
Instant colour! Gotta love onion skins. I simmered the wool in the onion skin juice for an hour (onion skins removed this time as slimey onion skin is a pain to pick out of the wool) then allowed it to cool and left it overnight.
And here it is, still damp, on the washing-line. Glorious rich colour..
.. and partially dry, still a rich rusty gold.
And the result! The skein is a bit untidy because partway through simmering the wool in the onion dye I snipped a length of wool for a little afterdip experiment. I cut the snipped length in half and made up two jam-jars of afterdip - one acid (white vinegar diluted with water) and one alkaline (2tsp of soda-crystals dissolved in water). In the picture below you see the strand results on the lolly-stick. The left-hand one is from the alkali afterdip and the right-hand one is the acid one, which as you can just about see is a bit yellower.