It isn't recommended to underplant citrus. They don't appreciate competition within the dripline.

Agree with above comments. However, : ), the ground-hugging thyme has crept under the lemon tree's branches somewhat, and it's an attractive accident. But it's still many inches from the trunk, and absolutely flat.

I agree with the other posts...In my experience it's not advised to underplant citrus.

I have azaleas and impatiens in pots under my citrus and its very pretty. You don't see the pots at all. I would have to say that my citrus has liked the nitrolized fir bark as a mulch that was suggested to me. My tangerines are open at the bottom so I can remove fallen fruit. The low bowls full of impatiens are very pretty below the foliage and don't compete whatsoever with the citrus roots.

Or just throw some alyssum seed around the edges of the dripline. The roots are tiny. The flowers attract beneficials. When they start looking ratty, just pull them out and new ones will sprout and look pretty again quickly.

I like the alyssum idea to attract beneficials!

I've got some dicondra growing under mine.

I have nasturtiums that grow beneath my citrus every spring.

Do like they do in Italy and underplant during the winter and spring with fava beans. All the lemon and orange orchards around Naples are underplanted with fava beans in the spring.

Like Mikey, I have nasturtiums under my citrus trees. They reseed themselves and I tell myself that since they are in the legume family they don't take too much nitrogen from the soil.

Citrus benefits enormously from permaculture enhancing the soil and attracting symbiotic insects