Herb growing in South Africa - Gauteng

I would like to start growing herbs in some outside flower boxes. I want to plant stevia, lavender, tea tree and then I'm not sure after that. What else would you advise for someone starting out?

The problem is that I am not sure what your climatic conditions are like, since we do not have a zone map for Africa. However, from my memories of my visit to South Africa and consultation of a globe to check comparable latitudes for Australia, I would guess that the most southern coastal tip of South Africa is Zone 10, further inland is zone 9 and then it goes up to zone 10 and tropical as you go North. Our catalogue and the "Richters Herb Growing Infobase" found in the "Richters InfoCentre" in the "News&Info" section of our web-site www.richters.com give you the zones that the plants are expected to survive out of doors in.
You do not say what you want to use the herbs for, but for the beginning culinary herb grower check the zones against what you think is your zone, for the culinary favourites found on the suggested list of plants for the seed display given in the "Commercial Retailers" section (page 73 in the 2007 catalogue). The seed collections found between the herb seeds and the Everlastings (Page 56 in the 2007 catalogue) are another good source of easy-to-grow herbs and are sorted by use.