Do your trees a favor and don't plant in the root zone or disturb the roots, including but not limited to piling soil over the roots, against the trunk or building brick borders around the trees then filling them with soil. I know this is not the answer you wanted to hear but this could cause the slow and eventual death of the tree and mature trees cost thousands to remove.

Yes. Leave the root zone alone. Not to mention that magnolias are messy.

Dan

Planting small plants (digging small holes) shouldn't significantly affect the tree's roots. Adding a light layer of mulch (2"-4") will actually benefit the tree. Even adding compost in the planting holes you make won't hurt the tree. As Iforgotitsonevermind mentioned, don't pile soil (or mulch) up against the trunk.

I'd google plants for dry shade for more recommendations than you'll ever need.

Here is a link that might be useful: Plants for Dry Shade

Are the magnolias deciduous or evergreen? The garden character of these two groups are like day and night. Saucer, star, lily and the many deciduous hybrid magnolias lend themselves to multiple spring color effects like underplanting with sheets of blue-flowered spring bulbs such as bluebells, grape hyacinths and squills. Evergreen magnolias, especially the heavy, shady and messy bull bay (the name says it all) don't have the same flexibility. In fact, in The Complete Shade Gardener G. Schenk says southern magnolia doesn't really belong in home gardens at all, with its deep shade and continuous production of litter all summer.

The 'Little Gem' cultivar, with its small parts is less overbearing than most other forms sold - but is less hardy and prone to break under wet snow.

The fleshy roots of none will appreciate much digging among them. Very small plants like dormant spring bulbs could be carefully inserted among the roots of a long-established deciduous magnolia. I wouldn't attempt to carve out full-sized planting holes unless I found spaces that were without magnolia roots, for some reason.

Definitely don't tear up sections of small roots or cut, scrape or gouge larger ones.

"In fact, in The Complete Shade Gardener, G. Schenk says southern magnolia doesn't really belong in home gardens at all..."

Remind me not to waste any money on Schenk's book. There's something wrong with that dude!

IMHO and from experience.

Lily of the Valley do very well under a Magnolia. Been there, done that. Only suggestion I have is to put some kind of sunken border around the area where you want to confine the plant growth. Roots are very shallow, but they do reproduce like rabbits!

Plant pips 1" (2 -3 cm) below soil surface. Roots are shallow.

If you want color variety, there are two very nice versions. White and pink (Lily of the Valley Rosea).

Here is a link that might be useful: Lily of the Valley

Southern Magnolias look best with branching all the way to the ground. You may just want to move the 8x8 bricks and used them to make a separate flower bed somewhere else. They spread a lot and they are very messy in the spring. Mine has a lot of surface roots and its very hard to even grow grass around it. Good luck!

would the Lily of the Valley work under these BIG trees?

To repeat oft-repeated above, as long as you don't disturb the roots.

Dan

I may not be a licensed Horticulturalist, or even a commercial landscaper, but I am a long time gardener of "flowers"... I put beds in at my now deceased parents home for them to enjoy for years, because I was too young and too broke to own a home of my own yet... their home was just practice for mine... Anyway, after finally buying my own home over 20 years later, I planted a Southern Magnolia. That was 7 years ago, and it slowly grew... I nurtured it and fertilized it, but in my honest opinion, it looked like it was sad and lonely, and well... even though it was growing, it did seem to be doing it slowly.... YES, I know Magnolias grow slowly, but... AFTER I planted some flowers below, carefully as not to damage or do too much damage to the existing roots I noticed something. Maybe it was just coincidence, because at the time I planted the flowers it had been in the ground for 5 years... but that Southern Magnolia started growing more vigorously and showering me with lots of blossoms. Unfortunately, my husband decided to burn the dead grass and weeds that had died over the fall among my newly planted flowers around the Magnolia, (because my neighbor won't cut his weed field they blow in and take over my flowerbeds every year... they are out of control, and I have spent hours pulling them every day all summer until the temps go over 85, and then I wait until the temps drop down below 85 again in late summer early fall, so I can resume my garden duties safely again.)... anyway, he let it get too close to the tree... scorching the trunk and causing some trauma to the tree last year... BUT I didn't give up on it and I planted some Annabelle hydrangeas loosely around the perimeter about 10-12 + feet away from the trunk of the tree, and planted more perennials, it seems to have an affinity with trench lilies, day lilies, chrysanthemums, Asiatic lilies, elephant ears, pachysandra and liriope... Once the flowers began to bloom my magnolia tree seemed to perk up and grew some more despite the damage, and still showered me with lots of flower buds. Because of my husbands mistake one side of our magnolia tree is lacking new growth, so it is a bit bare... so I decided to plant a clematis to grow up that side to fill it in during the summer months. I am beginning to believe that they are happier when they are NOT ALONE... several years ago, I read that plants communicate with each other through their root systems and the mycorrhizal network... I think they make each other happy, and as a result, both species (the tree and the flowers) are rewarding me with many blossoms to enjoy. *Now if only they had the ability to tells weeds and grass to STAY OUT! ;o) I think the only suggestion I would make, or what I would do differently, is to plant your flower bed (not a raised bed) around the magnolia tree during the same growing season that you plant your magnolia tree and you will be able to avoid disturbing the root system later, and yes in the South... the soil gets so hot here in the summer that if you do not put mulch down the plants will either die or dry up even if you water them daily... Someone mentioned that magnolias drink a lot of water, with that in mind, I suggest that you select bulbs, corms, rhizomes, tubers, perennials, etc. that are "drought resistant/tolerant" so that they will be able to weather those really hot dry summers we occasionally get, like the one this year... the Drought of 2020 that nobody is talking about!!! Driving around my farm community I am seeing fields of corn and other crops whose foliage is drying up and turning brown... Oh, and I planted daffodils too, but many of them didn't make it... possibly they were eaten by voles. If I had more time, I would have planted more early spring bulbs to enjoy earl on in the flowering/growing season!!! As for the leaf liter, I leave it be... its really just compost anyway!

Any photos you would be willing to share? it sounds lovely!