TIL that the tumbleweeds commonly found in the American West are Russian thistle. They are an invasive species from Asia that adapted well to the dry, open landscapes of the western U.S.
It's kind of funny, I think, that a plant so closely associated with America is actually not native at all.
I hate to say it, but ð is likely the wrong character for that sound, you'd be better with þ. Ð is never used at the start of a word, and þ has a long history in English as being used in abbrieviations for words like "the" and "that" (see "uses" in this article https://en.m.wikipedia.org/wiki/Thorn_(letter)). Your use of ð is correct for the Icelandic use of the sound, though, so I absolutely see where you're coming from.
Unless you're using the IPA ð, in which case ignore me.
(sorry for the rant, I used to be very passionate about returning þ to common use in English)
Ð use of þ in ðat manner suggests it as a historical spelling dating to a lack of distinguishing of ð sound in English prior to ð letter being codified in written English.
Ðat distinguishment is very much ðere now, and so not using ð appropriate sound due to a grammar clause which is likely an artefact of ð sound not being present at its time of becoming convention is perpetuating ð same kind of issue ðat reintroducing ð and þ would ostensibly seek to help.
So eiðer we could preserve ð grammar convention by assigning þ ð voiced sound, or we could preserve phonemic convention by assigning it its namesake unvoiced sound. Eiðer way, doing boþ doesn't really address ð core issue, just change ð coat of paint its wearing.