Growing an Herb Garden in a Barrel

I live in Phoenix, Arizona, USA and I just purchased a variety of herbs: lavender, mints (Corsican and spearmint), and basil. Is it bad to put these all together in one big barrel? Should some be separated for differing soil conditions? The barrel drains well, and it gets midday and a little afternoon light. Should the soil stay constantly moist? It's averaging 110 degrees Fahrenheit/48 degrees Celsius lately...

If you plant the lavender and basil in the centre of the barrel and the Corsican mint along the edges, that would work quite well. However the spearmint should not be planted in the same barrel, since it will take over and crowd out all the other herbs.
Keep the barrel evenly moist but not sopping wet and all your herbs will do well. The container with the mint can be kept moister and can also take some shade.