What aspect of a keyhole garden makes it retain water?

Keyhole gardening is touted as a great way to retain moisture in dry places but i don't understand HOW. My impression was that raised beds tend to drain better than flat gardens and therefore lose water faster.

I understand that, like hugelkulture, there is lots of organic materials in there and that humus retains water. What does a keyhole garden do that a flat garden with lots of compost wouldn't?

Of course, bonus points for watering the "compost pile" and the garden with the same water. I imagine that in itself cuts down on half the water you would otherwise have used.

For the record, i love the idea of the compost in the center. It means i only have to move compost once (source - garden) as opposed to twice (source - pile - garden) and that it effectively takes care of nutrients leaking out of the pile as they are leaking into your garden soil.

A few other questions:

will the center ever become so full it has to be emptied, or will the worms tend to redistribute it enough that it will never become a problem?

Urine has to be diluted 1:10-1:20 to be safe for direct application to plants. What if i was dumping a big bucket of "yellow gold" into the compost pile at the center of a keyhole garden? You think it woudl still need to be diluted? I imagine that the "browns" in the pile would lock up a lot of the nitrogen but would it be enough that you wouldn't burnt he plants? Lugging around 11 gallons of urine dilute would be pretty impractical, but what about dumping a gallon on the pile then giving it the weekly spray down with a hose?

I read this:

Gardenconstruction
Over time, the garden may lose its nutrients and start to become less effective. If vegetables stop growing well in the garden, and there are no pests or diseases that you can find, you may need to pull all the stones away, sweep away the old garden layers, and rebuild each layer of the garden. This is usually done every 4–5 years.

Woudl this be assuming they aren't adding any fertilizer beyond compost?

keyhole and hugleculture operate on similar principles. For some locations in the desert/arid areas, one would have to use a sunken huglekulture, and the same would hold try for a keyhole garden in such an enviroment.

Now as to how does it save/retain water.
The fungal network burn O2 and brown material releasing water.
The fungal network also gives the plants higher concentration of minerals thus the plants perform less water assisted mineral mining.
The green material in the compost are 80% water and instead of all of it evaporating away, some of it enters the plant.
The keyhole allow more water to infiltrate, due to the structure and soil cover of the garden.
.....

S Bengi wrote:keyhole and hugleculture operate on similar principles. For some locations in the desert/arid areas, one would have to use a sunken huglekulture, and the same would hold try for a keyhole garden in such an enviroment.

Now as to how does it save/retain water.
The fungal network burn O2 and brown material releasing water.
The fungal network also gives the plants higher concentration of minerals thus the plants perform less water assisted mineral mining.
The green material in the compost are 80% water and instead of all of it evaporating away, some of it enters the plant.
The keyhole allow more water to infiltrate, due to the structure and soil cover of the garden.
.....

This all makes sense to me except for the part where you say "...a sunken huglekulture, and the same would hold try for a keyhole garden in such an environment." Wasn't keyhole gardening developed in arid, hot parts of Africa? All the videos i see of keyhole gardens being made in Africa are waist high, give or take. This suggests that it is exactly opposite of what you just suggested (although, i would otherwise assume exactly what you said about not raising gardens in arid climates).

My question is why not create a hybrid of hugelkultur and keyhole design? By utilizing wood int he base of the keyhole garden you could increase the ability of the keyhole design to hold moisture... or so it seems. I think to much wood may defeat the keyhole design idea but a little may be helpful especcially in arid areas. Or, maybe I'm way off? Interested in other's thoughts.

John Lincoln wrote:My question is why not create a hybrid of hugelkultur and keyhole design? By utilizing wood int he base of the keyhole garden you could increase the ability of the keyhole design to hold moisture... or so it seems. I think to much wood may defeat the keyhole design idea but a little may be helpful especcially in arid areas. Or, maybe I'm way off? Interested in other's thoughts.

I'm under the impression that part of what makes a keyhole garden is that it is filled mostly with organic materials. Filling it with wood is probably just as acceptable as phone books, cardboard or any other carbonous (guess i made a new word) material. One advantage i perceive of hugelkulture mounds over keyhole gardens is that since hugelkulture mounds are longer, you can use large pieces. Whole trees even. A keyhole garden shouldn't be more than 6ft diameter so wood would have to be chopped up.