This hyacinth bulbs are felted in a washing machine.
(40 degrees 1 hour)
I used diffent yarns from my stash (only non-superwash).
To be sure that your yarn will felt knit a little test swatch and wash it.
For one bulb you need about 10 grams of brown yarn, 5 grams of white and 5 grams of green yarn.

Worsted yarn (non-superwash), mohair