Drawing Stage behind 3d scene in libgdx

Question

I am trying to draw a stage (with a parallax effect) behind my 3d scene in libgdx (as a background). When I call stage.draw() before screen.render() i can only see the 3d scene. When I call screen.render() before stage.draw() i can only see the background. Is there a way to make the screen somehow see through?

I am calling:

stage.act();
stage.draw();
screen.render(delta);

My render() operation in screen looks like this:

Gdx.gl.glViewport(0, 0, Gdx.graphics.getWidth(), Gdx.graphics.getHeight());
Gdx.gl.glClear(GL20.GL_COLOR_BUFFER_BIT | GL20.GL_DEPTH_BUFFER_BIT);
modelBatch.begin(mainCamera);
modelBatch.render(instances, environment);
modelBatch.end();

Answer 1

Okay, so I figured it out:
Instead of calling stage.act() and stage.draw() before screen.render() ,

I simply called stage.act() and stage.draw() in the render() operation after

Gdx.gl.glClear(GL20.GL_COLOR_BUFFER_BIT | GL20.GL_DEPTH_BUFFER_BIT);