I've been building hügelkulturs for many years. I recently looked through some of the recently published
books on the topic and it seems that it's still being done the same way.
So, I'll go over what I call the basics, because there's not really a ton of anything and it's all basic. LOL
1) Big log bottom -- this is from whence your Hügelkultur derives its longevity.
Avoid hardwoods that are slow to break down OR add in a fair amount of soft wood, such as pine. People will debate what you can and can't use when it comes to wood, but I've always done fine with a nice blend from the surrounding area.
Oak Walnut and Cedar are known for a very slow rate of decay, which is not exactly what we want, soooooo make sure to keep that wood to less than half of your base.
2) The Base, Height and slanting sides -- ideally, a 6' base at 6' height (to account for settling/compacting) and the angle of the sides at no more than 45°... especially during the first year of establishing your mound.
Eventually, you'll see things settle down to around 4' high and the slant of the sides will not matter once your Hügelkultur is established... things won't roll down the side, especially with wind and rain.
When they do roll down, put them right back up there.
3) Twigs and Branches -- this next later is wood that will break down much sooner.
4) Nitrogen and Other Nutrients -- this layer is where you put the
yard clippings... Grass is full of nitrogen and other nutrients that are less readily available from the carbon-contributing wood.
5) Watering -- Some might be required depending on your climate during the first year, but after that, the big wood will hold the water quite well.
The wet wood will create a number of goodies including fungus growth.
6) Mushrooms -- The Eastern Shore of Virginia supplies the massive
hay bales to Pennsylvania mushroom farmers. The hay is rolled at the end of the season and sits for weeks to months before being taken north. By that time it has become the perfect medium for mushroom growing. I would suggest research but I'm pretty sure the best/popular mushrooms are best grown using hay bales, so you might want to consider that.
7) Dirt -- The final layer...
It does not need to be composted dirt because this whole mound is a composting machine.
You can mix in anything with that green layer, the same as you would your compost; this is the way I've always done mine.
Logs are relative -- They do not need to be 36" tree trunks to qualify but you probably want them to be 6" or larger.
Cut to a manageable length and drag with your truck or
UTV.
Build or buy a truck bed davit to hoist, move/load and place the logs to make things easier.
9) Super wet
land --. I have typically used old wooden
pallets, especially weathered ones, to fill a wet area, such as by the creek where someone previously thought they could dig a huge pit and make a
pond.
Spoiler Alert -- that only makes a mud pit.
Since I need multiple layers, I start with spreading wood mulch over the entire area and then make a "dock" of pallets down to the creek. These pallets are in their usual orientation, making them easy to walk across. I backfill the pallets with wood mulch (courtesy of Asplundh) and grass clippings... which will lead to rooted growth which will stabilize the earth.
From there, I cover the area in pallets, which I flip upside down. This orientation makes these quick and easy to backfill with the wood mulch-grass clippings mix. The topside, having more boards, makes a solid surface on the boggy soil and will absorb water. The backfill-mix will absorb some moisture and, because it is a "hot" mix, it will cause some moisture to evaporate from the pallet wood and the surrounding soil.
This leads to great growth of grass and natural flora.
If necessary, and it's is at my new house, I will add another layer to the entire area with pallets in the same orientation for the same reasons.
I want access to the creek so that I can throw on chest-waders and go in to "dredge" out some fertile mud/muck for the Hügelkultur etc.
Later, I can build a Hügelkultur atop this area once it's more stable and able to bear weight.
Eventually, this area will return to the more compact soil that it was prior to it being dug out.
10) Length & Shape -- in the past, these mounds were integrated into the defense plan of a settlement, for obvious reasons... so length and shape are completely up to you.
I am leveling my entire "front" yard by gradual means using terraced Hügelkulturs. They will hold my gardens, flowers and grapevines while I fill the space between them over time.
I might leave them a bit lower than my mounds OR I might then begin to revitalize my Hügelkulturs by adding new layers atop the old, so that I keep them going for decades AND maintain a nice working height of around 3'-4' above grade.
To be honest, of you want a giant round mound, because you have a big mound of old dead tree trunks someone piled up in one spot, then go for it!
If you want it straight, then INSTEAD of pulling out bottom logs and disturbing the decay process, consider cutting off anything beyond that 6' base width.
I use a battery powered 80V Brushless Motor Worx 24" chainsaw for sawyering and planking (with a Ripping Chain... 10° instead of 30°, as I recall) with my favorite chains from Australia. Archer chainsaw chains have proven to beat Oregon and everything else.
No need to work harder if you don't need to... Which includes digging a swale.
That's not necessary except in the drier/arid climates where it will enhance decomposition and improve water retention in the wood.
Otherwise, digging a trench means adding that much more material in order to be at a certain height above grade.
I doubt that I've supplied anything new or useful to y'all but hopefully it will be found useful by future folks who stumble upon these posts.
~Tex