It's really hard to find info on what plants grow well with citrus trees, lemon in particular.

I live in a rental place with a fully mature lemon tree, and really want to plant beneficial companions around it so I dont have to deal with the grass and burr clover that are taking over everywhere. The lemon tree is about 50ft. away from a fruitless (so annoying) mulberry tree and like 10ft. from a juniper. There are also rose bushes about every 10 ft. on this property.

So far I've found that these are companions for citrus trees:
dill
yarrow
thyme
marigold
borage
cosmos
calendula
clover, alfalfa, peas (legumes in general)
fennel
lemon balm (or any mints)
parsley
tansy

Anyone know of anything else or if any of these are wrong? Maybe some other perennials?

I want to draw up a little guild map, when I do I'll post it up here..

Citrus are fairly shallow rooted for trees. Something to keep in mind when planning companions.

I will weigh in on the dill, though. It's in full flower right now in zone 8b. After it sets seed the whole plant dies. In warmer zones it's a cool season plant.

Those are all great choices for a citrus guild. You'll want to attract ladybugs, wasps and other predator insects to keep the aphids in check.

What kind of lemon? If it's a standard Eureka lemon, they are very hearty and outcompete and outgrow just about everything. Meyer lemons, in my experience, as much less aggressive growers. I killed 3 Meyer trees before I finally got my existing tree to take off—and that's saying something because I never loose trees. It was so frustrating.

Nasturtiums self seed and are a nice bio-mass producer. The flowers are edible and make a nice companion for citrus guilds.

stinging nettle does well in deep shade and seems to do well in dry conditions as well. I just posted my stinging nettle pesto recipe in the kitchen forum. Lady bugs like it.

If left untended, lemon balm can be a bit invasive, like mint. Stay on top of it.

If you're growing thyme, throw in a couple of rosemary plants as well. One upright, and one creeping. They are good friends in the garden, and once established, they'll do well in dryer conditions. A well established lemon tree will suck the water out of the soil pretty quickly.

Fennel is a nice dynamic accumulator. Once it seeds, you'll forever get volunteer fennel plants coming up. But try to pull the ones you want out while they are young, as they send a thick tap root pretty deep and are tough to thin once they've taken deep root.

I think its lovely that you'll have a little herb garden under your lemon tree. Once established, herbs don't need much water --- at least perennial herbs tend to do well in dry conditions.

Happy guilding!