I have a small yard surrounded by retaining walls and concrete. I have beds with mature bushes and flowering trees like lilacs rhododendrons and dogwood and perennials.

I notice that when I dig a nice hole, struggling with the roots of these bushes, to plant new perennials, they do well, growing larger for the first 2-3 years, but then decline rapidly and eventually stop returning. When I dig up to plant a new something the roots are back. Clearly my bushes are bullies, lol, choking their smaller neighbors. I'm wondering if anyone has had success delaying this process with some type of buried boundary around the perennial? I'm thinking maybe cutting the bottom out of some 10" plastic pots to make a ring around the base of the plant? Or perhaps lining the hole with multiple (15-20) layers of newspaper? I know these are only temporary and the roots will eventually return, but if it can buy me another 2-3 years I'd be willing to try it.

Sorry no one answered you, but the idea won't hold water. Some trees are compartmental- you kill that root, you kill that side of the tree. Some bushes throw poisons around them which insure the fate of anything planted under them. There are always the main roots, but trees/bushes that survive in arid areas also have quick small roots that reach up and grab all available water. I have pine trees- well away from my raised beds, but, where you water, that's where they grow, so I clean the roots from my beds, containers, pots etc even when they aren't under a tree. Sometimes the roots grow straight up into a pot on the ground, so I won't grow anything needing deep roots near the other bushes. Good luck with your tries, tho

This is an old mature yard so there are tree and shrub roots just about every where. I just live with them and my expectations of the perennials is some what diminished. I know that my peonies will not be as big and floriferous as they would be if they were not competing with the roots. They do need extra care with water and nutrients to make up for the competition.

I feel your pain, Paula. I had to remove a dead dogwood a few years ago and I'm still encountering it's roots. Such a pain in the rear. Usually I take a saw to the offending root and do my best but I can't always get it all out so I have to plant elsewhere. The property has had several large trees and shrubs removed over time. the trees were dying or dead. the shrubs were old pink azaleas and I detested them. still every now and then I hit a root. I struggled finding a solution for you but the only way around your issue is perhaps nice big containers and plant the bed areas with annuals that won't grow huge root systems. I know this is not the way you'd like it to be but I'm stumped-pardon the pun!

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