• Post Reply
  • Bookmark Topic Watch Topic
  • New Topic

Hugelkultur bed on top of concrete - Is it possible

 
Sunny Soleil
Posts: 18
  • Mark post as helpful
  • send pies
  • Quote
  • Report post to moderator
Hi folks, I've been asked by a school community garden if they can build a hugelkultur bed on top of hardcore [sort of concrete]. I wasn't sure so thought I'd ask here.. I've only ever built them on top of earth, grass etc. And I'm wondering if there would be an issue with drainage etc..


 
John Brower
Posts: 10
  • Mark post as helpful
  • send pies
  • Quote
  • Report post to moderator
The short answer is yes.

I would really recommend building up the bed as much as possible. Like you said drainage is going to be a problem, and the concrete will heat up and dry up way faster than soil will as well as release alkalinity into your growing space. Especially if the concrete slab goes outwards past the bed you are working on, the hot concrete will spread it's heat. Take that into account when selecting your plants. I would recommend about a 4-6-inch layer of woodchips or leaves , topped with some 4-6 inches of sand topped with as much compost / topsoil as you can gather up. You may also consider a barrier over the concrete... If you're going to buy soil, I'd recommend the kind of potting soil that retains moisture.
 
Sunny Soleil
Posts: 18
  • Mark post as helpful
  • send pies
  • Quote
  • Report post to moderator
Thanks so much John. Actually the under surface is 'hardcore'.. not sure if that's the same word in America.. guess that's bits of broken concrete.and brick.. but seems your advice would be right for that as well as plain concrete flat.
 
Sunny Soleil
Posts: 18
  • Mark post as helpful
  • send pies
  • Quote
  • Report post to moderator
Another query.. If you are suggesting lots of sand and woodchips.. would that be a layer underneath the regular rotting wood and sod on top... and we're in the UK, south coast kind of Zone 7ish... what kind of plants would be best in a food hugelkultur bed.. as you mentioned the warmth... any suggestions... and as itis a school.. I'm thinking no plants that mature in summer vacation [they go back in September first week or so] .. when they're all away from school...
 
Mike Hamilton
Posts: 82
Location: north end of the Keweenaw Mi.
  • Mark post as helpful
  • send pies
  • Quote
  • Report post to moderator
we have ours on top of mine rock [bed rock] and their doing fine
hugel beds saved the day for growing crops up here in the Keweenaw

Mike
 
Donald Kenning
Posts: 78
Location: Tri-Cities, Washington
13
fungi hugelkultur trees
  • Mark post as helpful
  • send pies
  • Quote
  • Report post to moderator
Just putting my 2 cents in.

Since this is for a school of some type, I would say your budget on the job is limited or even non-existent. You probably have just a source of labor and not much else. I would say, get the local tree trimmers (Arborists) that chip up wood to donate to your cause. They can provide wood chips and possibly old decaying wood. Spread the wood chips on your land everywhere (not just where the hulgel pile will go) about 4 to 6 inches (or more). This creates horizontal drainage for your hugel piles. If an arborist can not provide you with enough old decaying wood, people give that stuff away all the time on craig's list. Just make piles of the stuff on top of the wood chips where you want your hugels piles to go. The next thing you will need is dirt (notice I did not say soil). Dirt is cheap or even free, soil is usually not. I live in a small town, but see people give away "fill dirt" all the time on their construction projects (also on craig's list). Take the dirt and put it on the chips that are not under hugel piles (the walkways). This dirt should be places on 3 to 6 inches thick. Now, what to cover the piles with... You can use the same fill dirt with no amendments. Just be aware, the nutrients would have to build up in that soil over the years and a successful hugel pile may take 2 to 3 years. If you are using fill dirt try planting nitrogen fixing plans and let them die and decay back into the soil. After the piles get planted, cover everything (piles and walkways) with wood chips (another 4 to 6 inches). Add lots of water then walk away. As plants grow out of the piles, brush away an inch or two of the wood chips away from the new plants.

Over the years. You will probably not need to apply any more wood chips to the piles but you may want to refresh the walkways every year or two. After about 10 to 12 years, You can make the walkways the piles and the piles the walkways. Just rake the fertile soil over the new decaying wood that you obtain then. Since the piles are all connected by a porous sponge on the bottom (wood chip base), the piles can "store" more water "horizontally". You should have a water source on hand to water the seeds you apply to the piles for the first week (many do not do this). Only use seeds (avoid transplanting).

Dangers ?!? Well, If the concrete is on a steep slope, I am going to guess that if you get a heavy rain, your "system" will wash down the slope. Even if your project is on flat ground, it could be that, areas around it will flood and bring in fast moving water. This will still wash away all your efforts. As you make this, you will always want to have forward progress (but you can not plan for everything). If you plan for flood, fire, and wind, I would say that you have most of the natural disasters taken care of. Other dangers are man-made. The use of petroleum based fertilizer, herbicides and insecticides might be something you do not do, but your neighbors might. In general, people who smoke will not start the pathways on fire, but try to keep the piles of wood chips inaccessible to outsiders.

Flood: The first thing that I would recommend, before a single wood chip gets placed in the area is to make a few holes in the concrete. I would start with an eight foot spacing and make each hole at least an inch in diameter. If the project is on a slope, shorten the spacing (1 foot per 1% grade) and increase the hole diameter (1 inch per 1% grade). You can do this with a chisel and sledge hammer, or rent a jack hammer for an hour or two. Either way, make sure the hole goes to the dirt below the concrete. To prevent flooding that is on the outside of your project from sweeping away your project, put a swale on the uphill side of your project. Make sure there are channels on either side of your project to transport the swale overflow down hill and away from your project. This swale can have plants and itself could be a wood core bearing structure (just not as much as the main hugle piles). The uphill edge of your project may not be completely on contour. You may need to do a lot of work getting it that way, or you may need to put gabion like structures in the dip of the swale. One thing you do not want to do is pile sand bags out there in the pouring rain.

Fire: First and foremost, your project will be moist at all times. You should have at least one pressurized water source on the property, with enough hose to reach every corner of the property. Even better if you had multiple pressurized water sources. Having no vegetation in the swales will help if the fire threat comes from outside the project. The swales and side channels will make for a good little fuel break to your project. And if plants are planted into the berm side of the swale, they should be watered down as fire approaches. Rocks do not burn, having a few well placed piles of them may also lower the threat of an approaching fire.

Wind: If you are in an area that can have storms that include high velocity wind, you may have to devote a portion your project to be sacrificed so that the rest can live. You need two things, to know which direction the high velocity wind would generally come from, and the average peek speed of that wind. Now, let's treat this like we would treat a flood coming across the property. We need to slow it down and dissipate the energy. Many farmer do this by planting a row of trees in the path of the wind. First of all, tree roots will mostly be unstable in this "artificial" soil. Trees need solid ground under them, in this project they will have wood chips and rotting wood piles with a little bit of dirt (at the beginning). Trees can come after about 20 years on the project. So on the windward side of the project you devote a certain amount of land to take the wind and slow it down. How much land? Here is where I take a guess. I would say 1% per 1 MPH past 40 MPH, you find as the average peek wind speed. So, if the peek winds average 80 mph, you should devote 40% of the windward side of the project to lessening the energy of wind. This can be done with loose rock piles, taller hugle piles, and plants you can sacrifice or are more sturdy in wind (even scrubs). Bear in mind, you will need to worry about wind less if you are not growing anything when those storms hit.

Man-made: You need to determine the man-made risks that your project is subject to, and handle them yourself (but it should be addressed).

Remember, many times the problem can be the solution.

 
Sunny Soleil
Posts: 18
  • Mark post as helpful
  • send pies
  • Quote
  • Report post to moderator
WOW.. that is amazing information... useful stuff for the future... We've already done the bed.. a few weeks ago.... BUT they may do more.. I've passed on the info to the landscaper gardener who's volunteering at the school...
 
Troy Santos
Posts: 35
Location: Southern Thailand
  • Mark post as helpful
  • send pies
  • Quote
  • Report post to moderator

Sunny Soleil ... so the bed's been built ... update? Pix? I'm interested.
 
  • Post Reply
  • Bookmark Topic Watch Topic
  • New Topic