Hugelkultur, Siberian iris and Tiger Lillies ???

[ID jit]

Goal is mostly weed supression and cleaning up a soft down slope which is mostly glacial till and not soil enough to support anything but random weeds.

I get the basic idea hugelkultur well enough, but what I am unsure about is the ratio of greens to mix in with the wood and branches, and how much soil I should cap the thing with. Will I need to supply some type of ventilation?

Basic plan is to do a buried hugelkultur, in tiers, so I can maintain the existing down slope away from the back of the lawn and have a soil fit to grow siberian iris in front and tiger lillies behind with maybe some other short stuff scattered about, topped off with bark mulch.

Am trying to figure out how deep of a trench I need to dig, which basically comes down to how much soil do I need to cap the thing off with.

Basic plan is to lay in some 2” - 4” 'logs' with some of the pile of last years grass clippings I still have and some semi-active compost. Lay in some sticks and branches over that with some more coffee grounds, scraps, last years grass clippings and some semi-active compost, cover it with the remains of the lillies, iris and hostas that came out of the front garden last fall and cap it with a mix if garden soil, compost and some of the glacial till which is really sandy.

So, any suggestions on how much soil to cap the thing with?

[applestar]

According to my limited understanding of hugelkultur -- not enough experimentation, ventilation would not be necessary since there would be plenty of air pockets and trapped air in the wood themselves. Be sure to include already decaying wood (logs, stumps, branches) for added fungal inoculation. Did you mention any fallen decaying leaves as well?

Amount of nitrogen might depend on if you expect to harvest crops here this year or in the future. An area that would be more of a wildflower bed might not need quick fix of nitrogen. I suspect adding green hedge/shrub/tree trimmings -- or chippered green wood -- might supply some of what is needed.

I think the amount of soil cap will depend on what you will grow on top of the mound as well as expected erosion. If you tend to get a lot of heavy weather, I expect you would need more and also would need to plant fast growing plants for erosion control. What are you going to plant besides the iris and the lilies?

[ID jit]

Applestar, thanks.

Erosion shouldn't be an issue. There won't be anything to harvest; this is more of a cover / fill kind of thing.

Only other things which may end up in there are some little bulb things which grow to about 6"- 8" with white or blue flowers once a year, and maybe some of green / reddish ground cover kind of thing, or anything else I need to beat back in the front garden. Have no idea what most of the stuff in there is. I didn't plant and am just taking care of it now.

So, the soil cap should be just short of how deep the roots grows, so the bottoms of the roots hit the hugelkultur stuff? Was what I was thinking, but wanted to check.

The iris is already there. Planted it 2 years ago and it is not nearly as prolific as it should be. Planted 3" diameter bundles of root in about a gallon of compost with some of the till mixed in. They need to be beaten back pretty much yearly in the front, so I thought they would kind of take over where I planted them. They haven't, and I am guessing it is lack of decent soil.

Will be putting the hugelkultur and lillies behind them, and maybe digging up the iris and build another for the iris.

[Kind of a no loose soil improvement project. The soil there current can barely support / sustain weeds. So no matter how the hugelkultur goes it will be a marked improvement to the soil.]

Was actually able to get some of the trench dug during the warmer days. Looks like it is going to be 30' X 2' X undecided depth.

[applestar]

I realize you want specifics. I meant more that it depends on what you grow there and what you expect, as well as just how much material you have to work with. People who make serious hugelkultur with backhoe and tractor/bulldozer make berms with enough soil on top to plant fruit trees, etc. Some hugelkultur "beds" are built in such a way that the area would eventually settle into more-or-less level ground.

It's certainly better not to allow the roots to reach the woody materials until they have had sufficient time to break down -- this would depend on the kind of materials used -- if you put the harder to breakdown stuff deeper and more decayed material on top just below the soil cover, the planted plants roots won't suffer from nitrogen tied up while the carbon material are decomposing as much.

I think I would also plant annual or 'easy to remove later' nitrogen fixer cover crops and/or shrubs/trees as nurse plants in this particular application.

[ID jit]

Need a logic check. Does this make enough sense to implement?

Problem:
Slight downslope leading off the property into a protected wetlands area of fine gravel-ish, alluvial till which will barely support weeds and will not hold any moisture.

Want to grow some 2' – 3' plants in there to hide the scrub brush, etc on the lower part of the down slope and remove the infertile brown patch and weeds.

Was thinking of some Bocking 14 Comfrey, but decided not introduce it here.

Known Factors:
Lillies root to about 1'. Am going to assume the same about the Siberian Iris.

Rhizomes (?) on lillies are at about 6” deep with the root spreading out from there. Iris are a bit more shallow.

Should make the soil depth deep enough to give the biomass time to decompose a bit before the roots reach it.

Should have some fairly rotted wood in with the all of the wood layers.

Should at least sprinkle in some active compost with each layer.

Available Resources:
Have a pretty much infinite supply of wood in all states of decomposition, 1/8” - 4”.

Have a fair stock pile of 'clean' grass clippings which is a soggy mess, and can get a lot more in season.

Have a pile of the leaves /fronds form the lillies, iris and hostas, and should be able to scavenge up some leaves.

Should have a decent amount of at least semi-active compost left after the strawberry container project.

Plan:

1. 6” - 8” of existing alluvial till / garden soil / compost mix.
2. 2” - 4” fronds from lillies, iris and hostas, some grass clippings, any leaves I can scavenge up and some active compost mixed in.
3. 4” - 6” of branches and twigs laid horizontally with some rotting wood, grass clipping and active compost added in.
4. 1” – 2” of grass clippings / 'greens' / active compost mix.
5. 8” - 12” logs and some rotting wood, grass clippings and active compost added in. These are going to be large branches (too small to cut up for fire wood) laid horizontally, dried / dead hardwoods.

Trench needs to be 2' – 2 ½' deep.

A wattle wall may be necessary on the downslope side. This will be able to be buried with the following hugelkulter on the down slope side.

Thanks much.

[ID jit]

This is actually working out sort of well. Digging the trench was significantly more work than expected and I only have two 4 foot sections done.

Tench is 2 feet wide and about 2 feet deep on the tall side of the slope. Put in a layer of grass clippings and short sections of cut up limbs (up to 4" in diameter) and mixed in some old fire wood that spent a bunch of time under a compost pile and was good and soft on the edges. Added in freshly pulled weeds sticks and twigs and random gallons of mulchy compost... basically a layer of what I had for greens and a layer of what I had for browns and active compost in between. Top 6" inches are a 50/50 mix of mulchy compost and sandy gravel run through a 1/2" screen.

Don't think I am getting too much air down in there, but it is holding height for now and the soil is moist without being soggy. Just need to make time to dig up and transplant the tiger lillies now.

[applestar]

Keep us updated with progress on this one. I love experiments and hearing how hugelkultur turns out. It seems to take a couple of years to see real results, but it all seems to make sense to me.