What to plant in beds infiltrated by fine tree roots?

We do yardwork for a friend here in town.  Most is maintaining already established perennial plantings and then filling two large raised beds (3' tall) with flowers and greens.

The challenging areas are those ground level beds near trees where the fine tree roots grow up into that soil making it difficult to establish things.

Lemon balm is doing ok there and orris root iris, some valerian, but other than that things don't thrive.
I've tried thyme and oregano, strawberries...a few other things and they soon die.
Bugle weed looks like it's going to make it.
I'm looking for more perennials mostly that might spread.

It's semi shady as is most of the yard.

What do folks do when establishing a 'forest garden' or any garden areas near large trees?

I think additional soil would only be infiltrated by roots in time also?

We aren't going to be using cardboard or any other weed barriers.

I'm there about once a week so things do get watered until established but I think the tree roots are using more water and nutrients than I can keep up with.

Good Morning Judith!

Do you know what kinds of trees are doing the infiltration? I wonder if they might have some allelopathic effect?

Hi Timothy!
The closest, and the one I suspect, is a very large crepe myrtle...one of the lovely thick twisty trunked ones and the other is a very large redbud....then bordering on the opposite side of this bed is a walkway with a pergola covered in wisteria whose main trunk is on the far side of that.
I don't think these fine roots are wisteria although I don't really trust it from past experience.
I don't think any of them are allelopathic?

Liriope is vigorous under crepe myrtle with part sun. Surface roots, where there is no erosion, can be a response to water-logged soils--is it heavier in clay there? A light mulch might help. Check soil pH. Crepe myrtles like a little acid, redbuds are more flexible.

Maybe also try bleeding heart, cranesbill geranium, violets or wild strawberry.

Judith Browning wrote:What do folks do when establishing a 'forest garden' or any garden areas near large trees?

I think additional soil would only be infiltrated by roots in time also?

We aren't going to be using cardboard or any other weed barriers.

Tough problem. I don't know about a forest garden -- the big trees fought for that space and own it, and they're not giving it up. The plants chosen would have to be mighty feisty SOB's to compete. There may be understory shrubs that work though.

For any other gardening, my solution would be container gardening. That would certainly work for annuals or smaller perennials.

How about cane fruit?

I'm also having this problem and one thing I've noticed is that my raspberries, which are in the ground less than 10' away from the trunk of a mature allelopathic Western Redcedar, are doing fine. Cane fruit seems like it would work!

Thanks to all for all of the ideas!

I have some thornless blackberries volunteering here at home...maybe I'll transplant some to this space if it ever rains again!

I think the fine feeder roots from the trees keep the bed dry and drained of fertility? The bed is edged in stone but not all that much above ground level.

Her yard plants are mostly perennials that are doing well with no water so I'm hoping to add more of the same.

A sharp straight spade cutting vertically down through the soil along the edge of the bed would likely help a lot. Does depend on this being a small proportion of the root zone, so as not to harm the tree though. You'll likely need to repeat it a couple of times per year to maintain it, at least while your new plants get established.

You might like to consider things like hostas as well - they cope with shade, and once established their root system is resistant to infiltration.