Rabbit, if you don't answer the questions put to you, we are not able to help correctly.

There are many plants that will grow down a wall, most that grow upwards need some support to climb, except IVY, that will cling to anything, anywhere and become a nuisance to control.

The right description of your retaining wall will get you the right answers.

Erica

Does Wisteria grow in QLD temps? I thought it was more of a cold climate plant.

Is there a 'hanging' geranium type?

ipomoea horsfalliae

I don't use common names, but the common name for this is Cardinal creeper.  I have grown it and it is beautiful, very showy.  You can train it to grow where you want it. 

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@azureline** wrote:
Japanese wisteria will only grow in the colder parts of Qld.
There is a native wisteria that will grow here but it is hard to find in nurseries.
I tried to grow several Japanese ones without success as it always died when summer hit.

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you mean hardenbergia? the purple one  grows biggish the white and pink ones grow small and wouldn't cover much. bunnings sells it.