01. Add Curves layer
First up, with our image loaded, add a Curves adjustment layer. Go to the Red, Green and Blue Curves channels individually and bring the top-right points about 60% of the way down.
We can adjust the relative levels of these points to create a cooler, eerier light. It will typically involve raising the Green channel's point and lowering the Red's. Every image you start with requires a slightly different balance of colours.
02. Balance the mid-tones
We can now balance the colours in our mid-tones. Going through each Curves colour channel again, I'm generally taking the mid-tones down and aiming to create a slightly warmer light in the mid-tones.
So if your grass is now appearing too blue, but your sky looks okay, you can go to your Blue Curves channel and bring the mid-point down until things look right. This is a great way to get to grips with colour curves.
03. Curve dodge
Our grass is still shrouded in darkness, so now we can add some soft, glowing moonlight using another Curves layer and a mask. This is sometimes known as Curve Dodge: it's simply a Curves layer with the mid-tones brought right up, creating a brightening effect, and a hide-all mask applied. We can now paint in this brightening effect using a soft white brush on the mask layer.
04. Balance the colouring
The advantage of a Curve Dodge layer is that we can now balance the colouring of this effect. I'm adding some warmth by bringing the red curve up and also bringing the blue curve up to make sure it still harmonises with the moonlight.
To soften this effect, hide the brush strokes and, to add a bit of glow, we can add some blur to our mask. With the mask selected, go to Gaussian Blur, in the Blur menu and select a high value of around 50 to 100px.
05. Add the moon
To add a bit more of a night feel, we're going to paste in a shot of the moon and a shot of some clouds, both taken against a black, night-sky background.
Once pasted in, and resized and positioned appropriately with the Free Transform tool, simply change the blending mode of both layers to Screen. You can use a mask on either of these layers to hide them wherever you need to.