Your question has become more interesting than I thought it would be. The term "meadow" is used quite differently by urbanologists, city planners, suburban folks, rural folks, ranchers and biologists/ecologists!
I'm a biologist. So here goes: terms to use for "open spaces": (apologies to cut and paste)
Meadow, mead: an unploughed, unmanaged open area.
Field, a ploughed meadow.
Hayfield, a meadow managed for natural grasses.
Bent, an area of grassland unbounded by fences or hedges. Much larger than a meadow.
Plain, a large open area, mostly flat. Vegetation will depend on rainfall.
Grazing land, ley, pasture, pastureland, lea, shieling: a field covered with grass or herbage and suitable for grazing by livestock
savanna, savannah - a flat grassland in tropical or subtropical regions.
veld, veldt - elevated open grassland in southern Africa.
Heath, an area of open uncultivated land, especially in Britain, with characteristic vegetation of heather, gorse, and coarse grasses.
Bottoms: flat low land along a river or stream.
There appear to be lots of other terms too.
Write, write, write! Not necessarily in that order.