Actually qep’a’ 2016 produced something close to one of your desiderata:

magh              Klingon plant that most closely resembles grass (n)

magh yotlh     lawn (n)

So I would say *{magh tIq yotlh} “field of long grass” for grassland, steppe, prairie, etc., though {Hatlh} might be better for open, uncultivated/unmanaged land. 

--Voragh

On Behalf Of Rhona Fenwick (QeS 'utlh)

Many of the words I've had on my personal wishlist for a while have been addressed in recent times, so it's growing pleasantly short. These are the main ones I still really struggle with finding a clean and concise expression for:

grassland, steppe (n)

sand (n)