Hey there again.
We have just done a garden bed too, but we are doing fruit veg and herbs.
You can make the soil better quality by putting in some good fertiliser and maybe some of those water keeper beads if the soil is really dry.
I know marigolds are quite hardy as we had them in our last house and we also have some litte climbing roses which seemed to do quite well.
If you are interested in doing some fruit and veg let me know and I'll tell you how we did ours for very little money!