Alternatives to wood for Hugelkultur beds

As the wood used in Hugelkultur beds is simply to hold water as it rots, is it fair to say that any substance that rots can be used instead of logs and branches? Using logs and branches leads to a need for a lot of soil to fill the spaces and allow to settling. I wonder how it would work to just use a deep bed of leaves and other vegetation? I have tons of leaves but not a lot of branches lying around. Also have lots of grass but I wonder if grass would be a good idea. I'm new here so I am playing with easy ideas to get started and get some good garden beds started. I'm in Michigan and have a yard of hard soil. I intend to have a good crop of compost next year and would like to put in some raised beds with wood chip paths in between.

As the wood used in Hugelkultur beds is simply to hold water as it rots, is it fair to say that any substance that rots can be used instead of logs and branches?  

As such it would not be hugulkultur (which is buried wood in mounds) but could have similar effect, and thus that is just wording.

One suggestion is laying out a mixture of grass clippings and leaves (as the grass will help to separate the leaves from laying against each other creating shingles.  Load them a bit at a time in a wheelbarrow and churn them by hand to mix.  Dump them into bed shapes that you want and with that mix you can really make tall steep slopes as it will hold together well.  Water it as you make the beds, and if you can do it before the spring that you intend to use it, it will ensure that it breaks down for when you use it as a garden.  You can utilize your abundant compost selectively in places where you want to plant.  

Another thing that you can do, which is both simple and very productive, is to plant potatoes in your sod { Dig a hole the size of your potato root for planting, water the hole and wait for it to drain, put some compost in the hole and put a potato in it}, then use the leaves, grass clippings and compost to mound the potatoes-watering each time you mound, both before mounding and the new material-this will build your mounds while producing a crop that incorporates a lot of vegetative/rooting/growth into your beds, adding structure to your soil system.

I do what you suggest...

As a sheep farmer I have tons...literally tons...of sheep manure that is about 50% sheep poo and 50% hay. They are not technically Hugelkultur's, but since I live on a hill, I often use this for fill for places I know I want to plant flowers, or berries. They do really well for years and years...

The wood in a hugel is not just about holding moisture, but also slow release of nutrients as it slowly rots. Part of what makes hugels work so well is this slow release over time instead of materials that rots and decompose quickly releasing their nutrients fast. It is also about giving fungus mycelium a good place to grow in. Much of fungus prefers damp woody material as a home. So hugels promote healthy fungal growth.

That isn't to say you couldn't find benefits from making mounds with less dense materials that decompose quicker. But they would not perform similar or have similar effects.

I'm right now in the process of an experiment that may help folks who have no access to waste wood. I have a pit that's 3' deep, 10' wide, about 30' long. I'm in the process of filling it in like a hugelpit, but using cardboard layering in place of wood. I put down a double layer of cardboard, then over that a layer of organic material....such as grass clippings, livestock pen litter, weeds, chopped brush trimmings, or whatever I have available including garbage, roadkill, etc. With each organic layer I add a bit of soil to add microbes and give some stability to the fill as it decomposes. I'm also adding a bit of sand or gravel waste, again for stability more than anything else. I repeat the process over and over, like creating a lasagna garden, but this fill is heavy on the cardboard rather than organic material. Also, I wet each layer of cardboard before covering it over.

This year I managed to fill the pit. In the past several months it has rotted down to about 1 foot in depth. By the way, it was covered with numerous beautiful blooms of dog vomit fungus. Cool! So I'm in the process of adding more fill right now. I expect to have to repeat the fill process a few times. Right now I'm coming out of a wet weather cycle, thus the fill material is nicely wet. The test will come when we have a drought year here. How well will this cardboard based hugelpit compare to the ones I've created based upon logs and branches. Will it retain moisture like the wood hugelpits? Or possibly more?  Time will tell.

I have access to all the plain cardboard I can handle, free for the hauling away. Plus I have plenty of pits on my farm that I would like to fill in then use for farm production....banana groves, fruit trees, gardens. Plus every few years we get droughts where the farm gets only 12"-15" of rain. So if these hugelpits work, I'll be one happy gal. I could be growing food without irrigation, a super plus.

That isn't to say you couldn't find benefits from making mounds with less dense materials that decompose quicker. But they would not perform similar or have similar effects.

 I'm not sure if that is necessarily true.  I have a feeling that deep soils, regardless of what the materials were to make them in the first place, if they were left without structural disturbance, will have similar effects.  It is ultimately the organic matter, the microbial communities, the fungi and bacteria and all the rest, along with the corpses of the previous generations of the same, that make stable nutrient cycling, holding nutrients, and not releasing them rapidly.  Fast decomposition only leads to leaching if the soil system is lacking.  In this case, the soil system will be building, and some loss may occur initially, but the same would be the case in a hugulkultur which has not rotted enough to hold nutrients yet.