Is it possible to build a hugel bed like a moat around a tree?

I am imagining a donut shape with no raised bed in the centre - a tree in the centre at normal height. Then raised bed up in a circle, with plantings around the sides on the outside slope. The tree would get water runoff from all the way around and the roots would be kept cool, but because no mulch is touching the bark it should stay healthy, meanwhile the plants are being separated from the thirsty tree roots by a good layer of branches, wood, mulch and soil so they shouldn't suffer too much from water competition. In dry, sunny, hot climates like mine plants tend to do well under a bit of shade. Perhaps some climber could be planted in the bed and it would use the tree as a trellis. What radius would such a hugel bed need to be from the tree all around to prevent the tree from being damaged?

Like most things in permaculture...it depends.

In a hot/dry location, this could actually prevent water from getting to the tree. If you are on a slope, it might be better to build it as a half circle on the down slope side. This would act as a swale, and capture water in the tree's root zone.

As for size, I would suggest determining how wide the tree will be at full maturity, and build it slightly outside that imaginary line.

If these are fruit trees, don't forget that you will safely need to use a ladder for harvesting. A close-in hugel bed could greatly compromise the safety of harvesting. Likewise, if they are trees that will be coppiced, you will need to keep that in consideration.

If this is to be a conventional, tall hugel, consider leaving an opening in it that is wide enough to allow you (and any needed equipment) to easily pass through to service the tree.

Another factor to consider is how sandy is the soil. If it is very sandy and drains too well, like ours, it would make sense to dig a trench around the tree and bury the logs deep enough that after covering them with soil everything is at grade level again. You'd have to find another use for the left over soil. I'd put the buried logs where the drip line of the mature tree would be. The fruit tree as well as the guild plants would all be able to access the stored water and nutrients in the logs. This could be done all the way around the tree even on a slope, except that you could berm it up on the downhill side, as mentioned. Over time, the hugel area will slowly subside as the logs decompose, so you'd want to fill it in with mulch and/or soil.

As I've mentioned on other threads, in our xeric forest, which is naturally open and park-like in appearance, whenever you find anything growing luxuriantly, almost without fail it seems to occur right on top of an old buried log.

piling a high layer of soil over existing roots of established trees CAN kill them..

if you do it you would want to plant a baby tree when you do it so the tree and the beds grow together...but the tree roots might grow up INTO the beds.

also if you are wet you could flood the tree in rainy weather..like a small pond.

so yeah as said above..it depends

Ok, hmmmm. I've never planted a tree before. I'm buying my first one (a lemon) today and I'm in the mood to experiment... Although sometimes my experiments are terrible so that is some good points.

Would it matter much if the tree roots went into the bed? I guess then as the bed broke down the roots would become exposed.

I do remember my mum telling me as a child that she was burying our (passed away pet) cat under a baby almond tree as it would grow better, so I'm thinking that if I'm going to bury anything with this baby lemon I'd better work out what it's going to be. I like the hugelcircle idea, but figure if it was a good one someone would have probably thought of it already. Perhaps it could have a keyhole access for easier picking.

Our soil is red clay but we have an evaporation rate 3x greater than our rainfall so it's unlikely to end up a pond. The usual problem we have with trees around here is that they set hard, pithy fruit if they are not irrigated enough.

Agree, you are training the roots to grow up to the surface, for the easy water and nutrients.

Bury out by the drip line is better. (And in the original hole)

Here in AZ, i think i am going to actually dig a deep trench out at 2 meters, bury some sticks and a piece of dripline feed hose,with tiny holes drilled in it at bottom of trench for summer water. and another trench out at 3-4 meters, and bury wood again. Can wait on the second one for a few years, but will contour for it now.

then profile the grade UP toward trunk. Think of a bullseye, with concentric circles, getting higher towards trunk. Want to force roots DOWN away from surface.
bottom of first trench prob gonna need to be over 2 foot deep, even with only 6 inches of sticks. gives you about 3" drop per meter.
Also, by burying dripline at least 6-9 inches, you don't feed weed seeds on surface. less weeding, but grasses and alliums should do fine.

Once the roots are past the first circle, then i will start adding mulch and companions.
By then, adding mulch height will only affect the small feeder roots, which typically die back all the time anyway.
I dont like planting anything on hills out here, prefer pits, but looks like it is gonna be required for long term trees.

i think you are more correct to go outside the ultimate drip line by several feet and allow access for excess water to drain away and then it should be fine, Sepp plants his trees between high hugel beds.

Clay requires a different approach than sand. Hugel beds should be raised in clay because if they were buried like you might do for sand, the logs would end up being too saturated with water much of the time. I agree with the other posts that the problem you would have by surrounding a tree with a high hugel bed in clay is wet feet for the tree. No matter how dry it is, all it takes is one big rain, and the tree could be drowned and killed. So you definitely would need an opening on the downhill side to let excess water drain out. It sounds like you're in Phoenix. We used to live there and we had several nice lemon trees. They grow well there without much soil amendment. The desert soil there is loaded with mineral nutrients and mainly just needs water and some organic matter. Give the lemons (or any citrus) a deep soak once per week during the hot & dry season, less often when cooler or wetter. The best way to set them up to be watered like this is to build a berm around the tree about where the drip line would eventually get to, and make sure the tree itself is sitting in the middle of a small mound in the middle of the circle. The height of the mound and the berm should be approximately the same. Fill the inside of the berm with water, and it should drain into the soil in less than an a hour. If it takes longer than that, the soil is very clayey and the tree may drown during the rainy season. Enjoy your lemons!

I'm in South Australia - supposedly the driest state in the driest continent, but a nice place to grow a lemon tree!

Ok, maybe the hugel around a tree idea sucks. Thanks for setting me straight

The Greywater Oasis guy has done something similar but without the hugelkulture. I think you could adapt his design to hugelkulture though.

http://oasisdesign.net/greywater/createanoasis/index.htm

He has different designs depending on whether you have free draining soil or not, and the water needs of the plant - eg a I think a tree in a wet climate is planted on an island in the moat so it doesn't get wet feet, but in a dry climate you plant trees in a sink. His mulch basins are designed for greywater, but I've used one like an encircling swale where the inner circle has only intermittent water. And as someone mentioned, if you are on a slope you can use less than a full circle.

He also talks about how to extend the pit out as the tree grows, depending on the drip line. I guess with hugelkulture you would just put that edge in one place and leave it there.

I'm getting a little confused in this thread with other stuff i've been reading...I live in Zone 6 and have clayey/gravelly soils. I am going to be putting in dwarf apple and possibly peach trees this fall/winter and want to incorporate a guild with some sort of water retainage system, i.e., hugelkulture, swales, swales/mounds. I thought trees should be planted down contour of the swales to recieve the slowed down infiltrated water created from the swales. Can you plant the trees on the mounds (hugel or just earthen) down contour of the swales or plant just down contour from the mounds? Is there advantage or any reason to ever plant tree up contour of the swales? THanks!!