Weedwood logs/bark can already be ground into Ground Weedwood Bark
It makes sense that you should be able to do the same with Giant Root. Perhaps, instead of making a new sprite and item for it, we can just have it give the same result as Tangled Root, and change the name of Ground Tangled Root to Ground Root, since both blocks from which they originate use the same textures anyways.

I don't think Rubber Logs should be ground though. I saw a vid where someone was questioning why Aspectrus would require rubber plank fences specifically. This could be explained by saying that rubber trees hold no aspects, and thus when the roots of the Aspectrus grip on the fence, there are no influences of other aspects that could seep in. You know... lore and stuff, people love it.