Yikes, that's a tough problem, Sheryl. Tree roots that want to invade are very troublesome.

My question to you is why did you say this: Is there a tree root barrier that I can lay down on the bottom of the beds after I've dug them out that will stop the roots and not cause moisture?

The part I am focusing on is your desire that the barrier not cause moisture. Why is this important to you?

If it were me I think what I would do after emptying those beds is pour concrete as a means of keeping the tree roots out as that is all I can think of that will definitively stop them. As far as retaining moisture I think I would just drill some holes an inch or two above ground level to drain excess moisture and sacrifice the soil below that to remaining soggy. A 2' depth is very deep and few plants are going to need that much.

I might be misunderstanding something though.

There is available plastic barrier material at lease two feet wide that has to dug into the soil and installed vertically at your property line to stop the roots. This is a big digging job and I would ask for the cost of having it done by a contractor. Al

Yea, had the same problem until I thought of using house siding. You can get scrap pieces from contractors in your neighborhood that are siding houses. Bought a trenching shovel and a little at a time, I dug a trench the depth of a piece of siding. Laid the siding in the trench, cutting any roots that are in the trench, then overlapping the pieces as you go. You will see as you dig that there aren't any roots down deeper than the siding. Any roots already in your yard will just rot! Fill in against the siding with the dirt. It worked great!!! The roots won't go thru the siding and turn around and go the other way. No more roots in my yard from the neighbors jungle...

How big are the pieces of siding you used?

cloudy christine, I used whatever I could get. 4, 6, 8 foot pieces. I just overlap the ends in the trench. The roots would have to be smart enough to find their way thru the overlap, and the siding does not rot! Worked great! Paul

Paul, I was just having trouble visualizing how you did this. You said

I dug a trench the depth of a piece of siding. Laid the siding in the trench, cutting any roots that are in the trench, then overlapping the pieces as you go. You will see as you dig that there aren't any roots down deeper than the siding.

The trench is as deep a piece of siding; how deep is that? When you talk about overlapping, I'm imagining plank-like siding boards horizontally place, with ends overlapping. But that doesn't make sense with the depth thing, so I'm confused. Probably there's something about how siding is sold that I just don't know. Please bear with me; this is an answer I need! I have to protect a new bed from the invasive roots of a sweet-shrub thicket.

cloudy christine, The siding I have been using is @ 9" tall by however long I can find. That means the trench has to be @ 9 1/2 inches deep, by 4', 6', 8' long, so that the top edge of the siding is just below the dirt surface. The siding is laid in the trench horizontally. You don't want it below the surface too much, otherwise roots will find their way over the top and back into your yard. The "ends" are overlapped as you continue on with the trench. Today I was adjusting some patio block that I have under my chain link fence (which makes grass trimming so much easier and also keeps animals from digging to get under the fence). I had to laugh, because I put the siding (root barrier) along the fence over a year ago, so as I took the block out to fix the dirt under the block, there was the root barrier with all the forsythia roots bunched up on the other side. They couldn't get thru. It made such a difference in my raspberry patch last year, not having the neighbors forsythia roots sucking up all the nutrients. It is a lot of work, but well worth the effort. You have to do a little at a time, and it will eventually get done! I don't know of any other way to stop the roots. I did the same thing on the other side of my yard where I have my tomato garden. The other neighbor has a huge pine tree about 4 feet from my fence. You know how it is, everyone has to plant their trees along the property line, forgetting that they will grow up some day! Every year when I till the garden, what do I find? Yep, pine tree roots. I put the siding root barrier in that area and now I don't get any roots in the garden. Paul

Just saw your reply, Paul. Thank you. It's a great idea.
I see now why I was confused. I'm imagining a deeper raised bed, and couldn't figure out how you were getting the height with the siding.