In ground Clay lined Hugelkultur Wicking beds – Fun with Charles
If you don’t know which method is best, try em all, I say.
Now some might do that separately, but I can see merits in them all that should integrate well, and after all permaculture teaches us to integrate rather than segregate.
The following photos and discussion is on the new beds I built on the verge at my place in Norman St Innaloo. While there are many reasons for gardening on ones verge the primary driver for me is that it is the best winter sun zone for winter high yield vege beds. I have a very large pair of box gums that shade a large area of my growing beds in winter. Also I still have enough space to park a car and trailer there.
Having tested and proved that plastic lined inground wicking beds work very well to conserve nutrient and water in our poor Perth soils over the last 2 years, I was never happy with the short term mechanics of putting a plastic perched water table in the soil profile. I have also found that the ‘wicking’ word is a bit misleading as the evaporation and condensation mechanism seems to be more active than the capillary wicking one in bring the moisture up . On several designs I had little wick and the water reservoir was still drawn down that the moisture made it into the soil profile above. Its not a deal breaker but don’t let your imagination be limited or your designs be defined by the understand that there must be a wicking element/substance.
So the next logical step in the experimentation and evolution seemed to be clay lined beds.
Bentonite clay is expanding clay used by dam builders to seal leaking dams or line them in low clay soil areas. It is these properties that allow it to be used to provide a medium term (2-3 years) seal below a garden bed in a similar manner to plastic sheet. While it an essential addition mixed into sandy soil, in this case the clay is being applied in a thick layer once a basin/pool/grave has been created in the soil profile.
This is a trial and while I expect it to be very successful I am not advising you copy it yet.
The reason for this method is with a long term view to moving to lower yield perennial food systems based on productive trees. Thus the fact that the clay, soil and moisture will in time be attacked by tree roots is not seen as a disadvantage but an aim. In 2-3 years I will have a highly clayed, fertile, soft, growing zone for fruit trees and larger perennials, and will move high yield annual vegetable systems into other areas and systems.
The in ground aspect of garden beds appeals to me, as I see raised garden beds as having very limited justification (unable to bend, elevation to keep out pets, school gardens), most of us should not have these as defining limitations. In ground beds use the soil as it should be, you are in contact with the mother soil, the soil temperature, and the whole. Also in this case I am building on the verge above essential services so at any time the council or service provider may come and dig up or at least need access. Large infrastructure heavy raised beds will be seen as far more permanent and thus cause more dramas.
So first we dig a grave, seriously, it looks like I have buried four very large people in my verge.
The idea is to dig out the top soil, retaining the best, and piling the worst plain sand to another pile. Once the hole is 30cms deep, flatten the bottom and round the sides. Dry clay has a slumping angle so trying to create steep deep clay zones is futile unless you apply it wet like glue. The dry clay is spread, broadcasted so that you are getting a continuous layer of 20mm or so along the base and up the sides about 10cm if possible. While the sides are not essential I think it will need less frequent watering in summer if I cam apply more water less often, and have less risk of the nutrients leaching/overflowing out. Note that this clay can expand 5-10 times its size once wet so a 20mm thick layer should be plenty once it hydrates.
My garden beds are generally 2m long by 1.2 wide. This width is used as you can access them from both sides and reach around 60-70cm crouching and leaning. Note these beds should never be stepped on and compacted. Use wide walk planks if you need to. I chose these dimensions as it allows me to frame the inground bed with the old Jarrah sleepers if needed. There are lot of benefits having a formal edge to your garden beds that is trafficable, especially when you have you kids. Basically the bed is 1 sleeper long by ½ sleeper wide, there is no need to ‘join’ them. This leaves the arrangement flexible which I like.
After the clay layer, and while it was still dry (if adding water to the clay layer alone you must do it via fine mist or very slowly else you will blast a hole in your ‘liner’), I threw in all the tree pruning’s, branches 50mm thick, leaves, whatever there was, and cut it up enough so that it had a low enough profile to be less than the 300mm deep hole.
This is the hugelkultur aspect. Sepp Holzer put in hole trees into his contour beds on the alpine slopes of the Kromatahof. While we don’t have frozen compacting soil to deal with (one of the main advantages of hugelkultur see more here http://www.richsoil.com/hugelkultur/ ), we do have sand with no organic mater or nutrient and water holding capacity. So the idea is to put lots of carbon in the bottom of the hole to create the ‘water zone’ of a wicking bed, and get lots of high nutrient compost and manures above it to grow on.
There are many things that can go wrong but if I learnt anything from Paul Taylor it was to Trust Nature, have some faith, given her everything she needs and stand back and wait to be amazed. Primary needs of water and nutrient retention and leaching reduction should be sorted, but unlike the plastic the further needs of evolution into a permanent perennial food forest should also be well supported.
In this case I was fortunate enough to have 1 year old 100mm thick street tree mulch everywhere, this was full of fungi action so a good 50mm layer of the best stuff went on top of the rough pruning’s. The idea here is that the fungi will migrate to the pruning’s to break them down further fast tracking the deep topsoil fertility development.
On top so the fungi I added the re-mineralisation, granite rock dust, basalt rock dust, and kelp powder was liberally broadcasted. The idea is that given it is fungal and bacterial networks that farm trace elements and minerals and trade with plants that I would make them nice and close to the fungi. Our sandy soils in Perth are very nutrient and mineral deficient it is essential to remineralise your food system. You are what you eat, if there are no minerals in your plants they will both suffer deficiencies and poor growth and not be much good for your body’s vitality after eating them. Rock dust is a slow release method of remineralising, while trace element powders can be bought from MultiTech and other companies these are highly soluble fine leachable additions. The leached soils occurred in the first place so adding more stuff that rapidly leaches away is not helping anything.
I have put off ordering good bulk compost, manure and vege soil for a year or two as I did not have the organic matter and clay in the soil to hold onto all those goodies. So I finally bough $600 of vege concentrate from Greenlife soils as I (my soil) was ready. This was the ‘soil’ that I used in the top of the wicking hugelkultur beds. This batch looks a mix of lupin compost and animal manures with rock dust, and smells like rich earthy goodness, but you would have to ask Paul and Linda to know. It is advised in normal cases to combine 50-50 the concentrate with your own local crappy sand base as it is very strong. While that’s sensible it doesn’t deal the cause of the crap soil in the first place, leaching, and poor retention capabilities in the main soil, so this is fancy imported soil is and expensive short term fix without long term soil carbon, clay and/or other amendments like Zeolite and spongelite.
The reason I don’t rate Zeolite and spongelite as essential in sand dominated garden beds is that while they do have a high CEC (Cation Exchange Capacity) they are ‘inert’. That is they provide structure, air and hidey holes for fungi and bacteria due to their sponge like structure, but they are not nutrients themselves. However there is already lots of sand providing that free draining, aerated soil, and we already must add essential organic matter, humus and compost etc which also has similar CEC (to Zeolite and Spongelite) and this organic matter feeds the soil microbiology.
Clay on the other hand is essential in creating high yields systems from sand. Clay is like the glue of the soil it makes everything stick there, water, nutrients, organic mater etc, it also has a high CEC so ticks all the boxes. The only other long term ecological methods of soil/system building is using plant based biomass mechanics to vegetatively ‘hold’ water, nutrients and in the system. While this is the best system and the only broad scale agricultural and land repair option it is harder and unfarmilar to most gardeners in small urban systems.
So rant over, if you want more on simple soil building and the various amendments go here - http://permaculturewest.org.au/resources/royalshow-2011 and check the soil info sheets.
I did add some sand to the vege concentrate to pad it out, maybe 100mm of concentrate, 50mm of sand and then topped with a bit more concentrate.
Now to answer those questions that are likely to come.
No I didn’t use any barrier to stop the soil/sand/compost from silting down into the ‘wet zone’ and mulch/pruning’s zone. While the water holding capacity of that zone will drop off I don’t see it as a deal breaker given I am evolving the beds to not be wicking beds over time anyway.
No I didn’t add/use a slotted agricultural pipe of similar to get water in and air in. While its important to do this to allow oxygen under the soil in a wicking bed to avoid anaerobic conditions again given the way I have made these beds I don’t see it as essential.
Where did I get the stuff ?
The clay was from a bulka bag, 1 Tonne (wool bail style) from Milne StockFeed, I don’t advise using 20kg bags at $25 each to do this as it might take 3 per a bed. If you can handle it, and or share it, a 1 tonne bag is only around $200.
Granite Rock Dust from Greenlife Soil Company, Basalt Rock Dust for a friend (sourced from Bunbury), and the Kelp (Italian) is from Nangara Rd StockFeed. And Greenlife Soils Veggie concentrate 5m3 bulk delivery enough to do 30 plus m2 of garden beds.
What can I plant in the beds, anything, unlike a plastic lined bed or one with a permanent barrier/reservoir these beds should be more like naturally moist soil and the roots can grow through the clay if they need to so larger perennials like Kale, asparagus etc should do better in the long term.
Anyway I am happy to field questions on the post on the terra perma facebook site, via email or if we get a comments section below this post. Cheers Charles