Is it okay to build soil up around mature trees?

eastwood2007 · Post by **eastwood2007** » Jun 19, 2007 8:03 pm

I want to put in some raised beds around some mature walnut trees. Question I have is if it is okay to build soil up on trunks of mature trees to about 18 - 24"? I will use 8" +/- rock edge and build up to around 18 - 24" at the center of the beds. Just wondered if anyone had experience with this?

Post by **Chris_W** » Jun 19, 2007 8:54 pm

In general, building soil up around the trunk of a tree will eventually rot the bark, destroy the inner layer that carries nutrients, then kill the tree.

Walnuts, however, are somewhat resistant to soil buildup. I've seen construction sites where they buried walnuts several feet deep and it didn't bother them. While working at one location I was concerned so researched it and found that walnuts were one of the few trees where burying the trunks may not damage them.

Still, I probably wouldn't intentionally advise you do it. If you are going to water the garden a lot then damage might still occur.

Some people will build a second rock wall, like a well, around the trunk to avoid damaging it. 8" to 12" of soil would probably not harm it, but 18 to 24" sounds like a lot.

wishiwere · Post by **wishiwere** » Jun 19, 2007 11:19 pm

Even burying the feeders roots out from the trunk can cause suffocation of the feeders, can't they?

eastwood2007 · Post by **eastwood2007** » Jun 21, 2007 4:18 pm

Well, I would certainly be in trouble if I killed the trees!!!

I have seen other gardens, though, where they have mounded the soil up around trunks, or that is the way it looks anyway. Do you suppose I just can't see the ring of rocks or whatever they used around the trees?

So, Chris, do you think 12-15" of soil would be okay? I have to bring it all in so I don't want to bring in more than is needed. How deep would the soil have to be for some of the large hostas?

Anyone else got any suggestions?

wishiwere · Post by **wishiwere** » Jun 21, 2007 7:49 pm

Keep in mind that even if it doesn't smother the tree feeder roots, then the roots will eventually make their way up through the soil to get to the water you'll be putting on your hosta anyway

So you will be contending with roots.

John · Post by **John** » Jun 21, 2007 9:48 pm

Yes, the roots will work their way UP into the soil in your new raised beds.

Is there any concern with being able to grow hostas under (specifically) a WALNUT tree? Doesn't that produce some chemical that 'poisons' the soil for certain plants?

I'm also wondering how far out from the trunk a protective 'well' might have to be to protect the tree and its roots from smothering.

wishiwere · Post by **wishiwere** » Jun 21, 2007 10:27 pm

I think other than the 'thunking on the hosta from the nuts', that chris or someone said they've had good luck growing hosta under walnut trees.

I'd be afraid to put anything that deep though a mature tree root zone for fear of killing it. It's hard enough for them to survive with progress cutting them down all around us

JaneG · Post by **JaneG** » Jun 21, 2007 11:22 pm

I've had a hosta bed under a walnut tree for six years and it's doing great. The juglone (I think that's the chemical) produced by the roots does not affect hostas. If you google juglone it's easy to find a lists of plants that will and won't survive under walnut trees. Here is one from University of Ohio

http://ohioline.osu.edu/hyg-fact/1000/1148.html

wishiwere · Post by **wishiwere** » Jun 21, 2007 11:30 pm

THanks Jane!

eastwood2007 · Post by **eastwood2007** » Jun 22, 2007 12:18 am

Thanks everyone! Well, I've been growing hostas under walnut trees for the whole time I have had them. Hostas are one of the few things that grow under walnuts. I want to add another large bed, but I am not digging anymore because of all the rock we have here. That's why I was wondering about putting soil up on the trunks. We currently don't get many roots coming up...don't know if that would be a problem???? Hmmm....Maybe I should take a pic of the area and see if anyone has any ideas...

wishiwere · Post by **wishiwere** » Jun 22, 2007 7:06 am

Pics are good!

bengal · Post by **bengal** » Jun 23, 2007 9:39 pm

Question I have is if it is okay to build soil up on trunks of mature trees to about 18 - 24"? I will use 8" +/- rock edge and build up to around 18 - 24" at the center of the beds.

Answer: no, it is not OK.

I have seen other gardens, though, where they have mounded the soil up around trunks, or that is the way it looks anyway. Do you suppose I just can't see the ring of rocks or whatever they used around the trees?

No, they didn't know what they were doing.

So, Chris, do you think 12-15" of soil would be okay?

No, 12-15" of soil would not be OK.

There. I believe I've given you my opinion.

Seriously, you may well kill the trees.

eastwood2007 · Post by **eastwood2007** » Jun 25, 2007 12:16 am

Thanks for weighing in bengal. What if I do like Chris suggests and circle the trees with rocks to keep the soil away?

Mary Ann · Post by **Mary Ann** » Jun 25, 2007 6:59 am

Charla, I didn't know there were that many rocks in Kansas, and Bengal sounds like he knows his stuff, but thinking outside the box, maybe you could build donut shaped beds around those trees out of lasagna-type ingredients (manure, compost, leaves, straw) without suffocating tree roots. I've built up beds around trees 18" deep and planted big pots there, renewing the decomposing materials with mulch as necessary.

eastwood2007 · Post by **eastwood2007** » Jul 10, 2007 11:49 pm

I forgot about this post....

Mary Ann, could you explain more about what you mean about donuts around the trees with pots?

bengal · Post by **bengal** » Jul 30, 2007 8:15 pm

No, I wouldn't say bengal knows her stuff. It's what I've read, however. And, since trees are expensive, I follow the "better safe than sorry" way of thinking. I am not sure where exactly I read about trees and the danger that mounding soil poses, but I have the feeling that it may have been in a gardening book by the garden writer Ken Druse.

You should probably do some more online research - maybe try to find some articles....
I gave you my opinion, but it's only that - my opinion. (I sure did sound definitive though, didn't I.

)

eastwood2007 · Post by **eastwood2007** » Jul 31, 2007 11:47 am

Thanks, bengal. I have slowed down my efforts on this project a little, and talked with a few more folks. Most like you, in that they think they have heard something about that, but not sure where or exactly what. I have decided I am going to do more research before I do anything. I am glad everyone responded as I never knew it could cause such a dilemma putting soil around trees.

I have also taken a second look at the area I want to build up and I think there is a way to do it without completely surrounding the trees. While most of these trees are just kinda scrubby walnuts, there are 3-4 nice ones and I would hate to lose those. Even though the scrubby ones have little value, they do provide the shade I need for my hostas, so I would hate to lose those either.

I am going to do a lot more research before doing anything here, as I don't really need the area till next spring. Please feel free to add ideas as you come across them, everyone. Thanks alot!