Going back to the shade issue, I find that many Plectranthuses are a
very good choice. Other plants that we grow in half or deep shade are Euphorbia carachias, various pelargoniums (the scented leaved ones), vincas, Saxifraga stolonifera, Arthropodium cirrathum, Iris japonica, Iris foetidissima, Ajuga reptans (see John's pictures of it growing in central Italy
here), Acanthus of course, Cymbalaria muralis, Glechoma hederacea, the Epimediums, all the Ophiopogons and Liriope, many Violas (they almost disappear in the summer, but you probably water in that bed) and some warm-climate Hostas that willl thrive on the water regime you provide to the citruses.
Some of the above (there are many others) can take dry-ish conditions, other require more moisture, you will have to experiment.