How do I get rid of the green stuff on the walls?

[Spails]

When I build my prison the stuff that looks like algae and the flowers don't go away, they stay on the walls and I want to get rid of them. Does anyone know how?

[Emmote]

Your gardeners / janitors should clean most of it. The only parts that tend not to get cleaned is your perimeter wall and that's because it's not classed as inside your prison.

[Frazzledragøn the Trustworthy]

If it counts as "outside of the prison", no jobs will be queued there.
If it is within your fences a janitor or gardener will take care of it.

However it is possible that some areas will be ignored, though I have no idea why they don't clean certain pieces of the path. Just leaving a crossing full of flowers and moss is strange.

[Charles the Bald]

You may need to hire more gardeners or janitors.

[leftbehind]

It's a confirmed layering (z-index) bug: http://bugs.introversion.co.uk/view.php?id=6867