So you want to make a circular flower bed round a large lawn area? What's casting the shade? Is it a tree as that would possibly take nutrients from the soil.
You grow whatever flowers you like Monica. It's your garden and there are no correct answers - only the combination of what you like and what will grow.

If you're starting a lawn from scratch, you'll need to buy a special grass seed for shady areas.

Why don't you click on 'S' at the bottom of this page to see 'shade plants' so you get some ideas for your border?

I'll add one piece of advice - a shady area is quite difficult to make bright and colourful with flowers - most of those prefer a good bit of sun, so select your plants carefully for those that prefer shade, and choose leaf contrast and colour as much as anything else - also variegated leaves.

For colour, I have 2 roses growing in different shady areas in my garden. One is Golden Showers and the other is Queen Elizabeth (pink).
Heucheras are colourful and most of them are shade tolerant.
Fuchsias would be great too. For a hardy one try 'Mrs Popple'.
Hardy geraniums are strong and colourful. Mine are doing fine in shade.

You don't say where in SA you are gardening, but in warm Mediterranean and subtropical areas your plant palette is going to be quite different from the cool Mediterranean and near-temperate areas near the Horn. Fuchsias and Hostas are going to be difficult in the hotter parts, while subtropicals such as Ixoras and Drimiopsis are going to complain in the cooler parts. You may want to get advice from your local garden center or possibly the local Ag Department office. I wonder, does South Africa have an equivalent to the United States' Cooperative Extension system?

Visit local gardens and nurseries for the best plants to grow in SA. And post photos for us to see!

As Penny f says, hardy geraniums are very happy in shade, and come in white, blues and all shades of pink. One of the best plants for shade is Epimedium - grown for their lovely leaves, often with bronze colouring.