in 1.1 forestries could plant trees on landfills iirc. I think the 2.0 change making landfills mineable caused that to stop. it's a small issue, but it really irritates me because the trees refuse to grow in the soft soil of landfilled places.

Also, just as a suggestion, what if artificial grass was available to turn deserts grassy to make tree farms in deserts feel more like terraforming? a good recipe might be 10 silica and 20 wood chips and maybe 20 fertilizer in a mixer so it will cost the same amount of material as a landfill.
note if you add fertilizer to the recipe, it will only be available when advanced forestries are unlocked, but if you want it to be available in the mid game, unlocking it with electric forestries or landfills would be good times.

I think the intent is to stop trees growing on artificial tiles such as concrete or tarmac. I've added an exception for "landfill" and "foundation" which is now in the Codeberg build.

Terraforming is a nice suggestion for a possible add-on mod, but I won't be adding any new content to the Patchset.