Adding Hugelkultur to Older Fruit Trees

I have 2 heirloom apple trees, a plum and two pear trees in our plot in north Idaho.  They are well established and produce nice fruit which we love.  Every summer for the last 6 or 7 years, I've hauled two 55-gallon barrels of water to each tree about once per week.  I'm nearing 75 and not in really good physical shape so the task is becoming more difficult for me each year.  Having learned about hugelkultur, I'd like to dig ditches (with a rented back hoe) around each tree and add some pine/fir logs to the holes to (maybe) reduce the trees' dependence on hauled water during the hot season.  So far, so good.  

My question is, how far out from the trunk should I excavate the ditches so as to avoid damaging the roots?  The pear trees are all less than 10 feet tall, the apples are less than 7-1/2 feet tall and the plum is about the same.  The soil is sandy clay with grapefruit-sized rocks, probably an ancient stream bank, but very well fertilized and mulched around the trees.

Any advice, rules-of-thumb or suggestions will be greatly appreciated.  

Thanks,
Sam McMillan

Hi Sam, and welcome to permies! I had a very similar situation to what you describe and here is what I did:

world's laziest hugelkultur thread

We're just now heading into the dry part of summer, so fingers crossed. I don't really expect to start seeing benefits for another year, but it is sort of like a massive layer of mulch at this stage so that has to be good. Digging trenches may be more effective but I could not be bothered either time- or money-wise.

There are more informed arborist on this site than me, I've been told that when one waters a tree, one must water the ground in a circle equal to the outter most extension of the branches and leaves....this implies that the roots mimic what the branches have done above them (but how deep?).

I've also heard of some breeds of trees which respond to a process called "digging the roots"

....I'm sure someone here will tell you how your species of trees will respond to root disturbances and if you can get away with digging the roots to some extent.

I am also curious about what would happen if you built a hugel culture bed on the north side of the trees, close enough to the living trees that some of the living trunk is covered:   can anyone say what will happen if he buries x feet of his trees' trunks?  Is there an amount of tree trunk burial which will kill the tree???

My thanks to Phil and Orin for their speedy replies.  I appreciate their suggested points but still have concerns.  My concern with brush / log piles on the surface are: 1. the natural decomposition will be slow due to (relatively) minimal ground contact, thereby pushing the time frame closer to my 80th birthday and 2. any surface piles will limit proximity access as I continue to haul water in the back of my pickup (ute?) while the hugelkultur is getting going.  I'm just spitballin' here so other opinions are welcome.

I've heard the concept of "one must water the ground in a circle equal to the outer most extension of the branches and leaves" that Orin mentions from other sources as well and it makes sense.  In this case the "circle" is only about 12 feet / 3m in diameter and our summers are quite dry so that makes me think any roots may be more than 1-2 feet / .3 - .6 m deep.  Although well established, the trees are relatively small for their age, possibly due to minimal water during their early life.  Assuming (always dicey) the foregoing is valid, I wonder if logs buried at a radius of 9+ feet / 3+m from the trunk and just deep enough to clear the soil surface will be close enough  to the trees to "do the hugel trick".  Maybe I'm just overthinking this, too.  As before, comments, observations, etc. are most welcome.

Thanks again.

If it were me, I would dig the ditches starting just inside the drip line and sloping deeper away from the tree. I would combine that with mulching as deep as I could manage from the trenches in toward the trunk. I would also top the mulch with some large stones (its amazing how well stones work in seemingly dry mountain environments to pull moisture out of the air).
Ideal timing would probably be to have this work done before the fall/winter precipitation comes so that the sky could soak all your hugel and mulch materials instead of you and your 55 gallon barrels doing it.

Hi Sam -

I wouldn't just pile logs and branches on the ground, especially in Idaho. You would need to cover them with a layer of grass and dirt to hasten the breakdown process (and that raises the obvious point of where to get the dirt). I also totally get the access issue, and that is why the one that I built is on one side of my trees (the side facing the reserve where the thirsty eucalypts are). As long as you confine your trenching to drip line and outward, you won't do much harm to the tree roots, and the dirt you excavate can cover the wood you put into the holes.

Give it a go and post pictures, especially an "after" shot of your trees next summer!

I love I Idaho and spend lots of time there. If it were me, I think I'd set a ring around the outside edge of the leaf canopy of the trees. Being Idaho though, I'd would be concerned about providing any fires with combustable material to create a prolonged burn especially around my fruit trees. Something to consider.

Wow!  Thank all you folks very much for the helpful tips and encouragement.  Based on my studies and your tips, trenches at the edge of the drip ring seem like the way to go.  Much as I'd like to do the excavation now, there is a bunch of slushy snow falling so the job will have to wait.  (I'm older but not completely crazy.)  I'm on top of D. Nelson's caution about wildfire fuel.  There is a mower on my wife's tractor that stays hitched up all Spring and Summer.  Yes, I'll post photos and update this post when the weather warms up.

I would like to add that this was my first foray into posting on Permies and I'm overwhelmed and grateful for the welcoming assistance and for this marvelous resource.  In fact, I briefly met Paul Wheaton about 8 years ago at Ernie and Erica Wisner's place near Missoula but never followed up on it.  It was my loss but I'm really glad to see this site is still flourishing.  Thanks again.