Frequency of refreshing for a green wall
Practical or most effective?

Green Screen work demands the following optimazation points to have it be effective.


flat even lighting, no hot spots, no dark spots.
no shadows,
no reflections,
the lighting has to be bight enough to register the green correctly, aka no noise.


Additionally, to help avoid hot spots, plan on a fresh drywall/plasterboard for that wall and when fixing, ensure sunk and smooth plastered nails. This will help you get a consistent surface for the green.

A curtain if it can be expanded to be absolutely flat with out any wrinkles might work,
but I think this will be very troublesome.

Painting the wall with the appropriate paint would be more effective.

When to repaint?

Establish a base-line video test, that is repeatable, same lights, same object(s), same camera. Run this in your post production chroma-key video track before each production use, and it should be obvious if the paint needs to be refreshed.

Paint source:
http://www.tubetape.net/servlet/the-5/greenscreen-screen/Detail

Disclaimer: I have not used this paint, it comes with no recommendations.