Jade wrote:

You didnt answer the question... how do you 'harden off' plants? I've never
heard of this before.

I have heard it in the aspect of nurserys.
A nursery raises seedlings in a hot house with high humidity.
They are repotted and moved out into the open, under say 90% shade, buy
only get daily watering. So they are hardened to water.

Later they might be movesd out to 20% shade cloth and thus "hardened to
sunlight.

Think of it as training the plant to adapt to different conditions.