Wicking bed

Merri Bee Organic Farm  is creating a natural system of perennial abundance to satisfy human needs in food, shelter, energy , community and wilderness, whilst restoring a cleared and overgrazed piece of rural land. Our farm is designed as a ‘closed loop’ in which the yields and by-products of one system are used to satisfy the needs of another, constantly circulating nutrients and harvesting water and energy via multiple elements. We aim to protect soil biodiversity and its many ecological functions. We are exploring and demonstrating these principles, educating and inspiring people to perpetuate the building of sustainable infrastructure. An example of this is
wicking beds
  We set up a wicking bed in a hurry recently to demonstrate how little water it takes to grow veges in this set up The growth has been phenomenal…. lettuce seedlings of the same size were planted in an adjacent, well watered and composted garden. The garden has had to be watered ( with a butterfly sprinkler ) once a week , the wicking bed only once a month. The lettuce in the wicking bed are 3 times the size of the garden lettuce. We dug a 150 ml deep level pit, lined it with black plastic and laid a 90 ml old storm water pipe we found at the tip on that .
We had previously cut numerous slots in the pipe and positioned the slots downwards, so the pipe won’t fill up with dirt. We put a plastic bag and a rubber band over the end of the pipe. Conveniently the pipe from the tip came with a 90 degree bend  ( elbow ) attached. We inserted another length of pipe in it, and set that up vertically. That’s your water filling pipe. We  then surrounded the pipe with small rocks at one end and woodchips at the other.

The woodchips were much lighter and easier to work with . I will see which end works best for the longest time. So you now have the 150 ml pit filled with aggregate which creates big air spaces between chunks, which will often be full of water. The aggregate essentially holds up the soil above. Place a thick layer of leaves or grass clippings , or a sheet of shade cloth on top of the woodchips or rocks. Then fill the bed with good soil and compost mix to a 350 ml depth. It can be up to 400 deep but no more, as the water can only wick up to a height of 400 or so. 350 is deep enough for most root zones. A drainage hole is essential at the level of the shadecloth. Otherwise a down pour or forgotten hose running would result in waterlogged plants. Which will die. You then hose or bucket water into your plastic lined gravel or wood chip-filled reservoir , via the fill pipe  until  water starts emanating from the drainage hole . In the event of a down pour, this drainage pipe or hole will ensure the soil doesn’t become waterlogged. In our case, water just begins leaking out at ground level (where the plastic liner emerges)  when the reservoir is full. I like the fact I can go away and pick some parsley while the running hose fills the reservoir. If I get carried away birdwatching the excess water will only benefit plants down hill of the bed.
After all this work and materials, plant your seedlings and water them in as usual.
 Prepare to be amazed as they thrive without any further attention from you for at least a month. That’s what we found, and we certainly hadn’t had much rain. See pics of the plants in the wicking bed just one month later, compared to the pale undersized lettuce in garden ( which had been watered with over head sprinkler every second day) My photography sucks, but I hope you can see the bigger and lusher growth in the wicking bed. Tried to deliver same amount of compost to both lots of plants also. I think the sprinkler watered lettuce bolted to seed soon after the picture was taken.
We want to experiment with  wicking beds as a grey water treatment system,  having trickled it first through a rock column then through a wicking bed planted with reeds  to remove nutrients . The reeds could be used for mulch. 
 A google search will reveal many different types of wicking beds and no doubt YOU will come up with great innovative ideas we would love to hear! My friend Tash Levy has successfully used bentonite clay instead of a plastic liner. We will be following her lead on our next one, as it is more natural and less toxic to manufacture and use than plastic. Thanks Tash!
 Update! EDMP plastic is safer than PVC. Pond liners of EDM or butyl rubber would be of the safest kind of plastic and possibly worth the extra expense. We will also incorporate a worm feeding station for disposal of vege scraps.
Every home in arid lands should have a wicking bed! 
Here is some further great info from Rob and Michelle Avis in Alberta Canada: http://www.energybulletin.net/stories/2011-05-31/bottom-diy-guide-wicking-beds
How Wicking Beds Work
A wick works through capillary action – the same force you observe when you dip a piece of tissue paper partially into a glass of water and watch the water climb the paper.  Wicking occurs in many materials; cotton, wool, geo-textile, soil, gravel and even wood to some degree. Every material has different wicking properties which you can test by placing that material into a glass of water and watching the water “climb” up. When one end of the wick is saturated and the other end is dry, it creates a moisture gradient, which drives the wick until the gradient no longer exists or you run out of water. With the earth box, one of the more popular examples in North America, the soil is suspended above the reservoir with wicks dangling into the reservoir pulling up moisture. As the plants use the moisture in the soil, it creates a moisture gradient (the soil is drier than the reservoir) which drives moisture through the wick into the soil.
Advantages of Wicking Beds
Wicking beds have a lot of advantages over standard raised beds and in-grown swale-based gardens:
·         They are water-efficient! Watering from the bottom up prevents evaporation of surface water (which occurs when you water beds from the top).
·         They are self-watering! Wicking beds are an especially great system to use in community gardens because they save people from driving every day during hot weeks to water their beds. A full wicking bed should irrigate itself for about a week.
·         No evaporation means no salting of soil. If you are watering your soils from the top with slightly water, you risk accumulating salts, because the water evaporates and leaves the minerals behind. Eventually your soil will struggle to support plant life.
·         They provide a lot of drainage in the event of a large downpour.
·         Since they’re raised, they will warm up quicker in the spring.
·         You can easily attach cold frames or shade sails or birdnets to them.
·         They are great for people with less mobility/flexibiity.
Disadvantages of Wicking Beds 
·         Are few!    *They cost more in time and perhaps materials to create than ordinary garden beds .
                * You can forget to water them altogether !

Our first wicking bed is going well, devoted to strawberries now. Second one has had a major problem.. I HAVE TO FIND TIME TO EXCAVATE  a large amount of soil out and see what is going on, because the reservoir always has water in it, it isnt going anywhere, but the soil is dry. Somehow poplar roots from a nearby huge tree have also  invaded it ,without piercing the plastic obviously, maybe through the jarrah sleeper joints?  So it is all a mystery.
 I have done a small wicking bed  lined with clay, it is going very well . I think the reservoir need filling more often and certainly doesn’t hold water for more than half a day but I think that means I didn’t use solid enough clay. It has a certain amount of sand in it. I used bentonite (as in no name brand kitty litter) , dry, as a layer over the wet clay, to faciitate a light pounding of the clay “pond liner” . It stopped my pounder getting heavy with sticky wet clay.
 Even though it only holds water for a few hours it is long enough for the soil above to wick it up. And for some reason, it doesn’t dry out for a week in high summer. No doubt during the other 3 quarters of the year it will  barely  need water.  I did put quality aerobic compost in at a rate of about 50 %. The strawberrys in this mini wicking bed with glass viewing window are growing well.

C Could there be problems with anaerobic conditions in the bottom layer of soil near the water reservoir? The rules are that you look down the pipe every few days and check the water level. You should only water again when the pipe has been dry for 1 to 3 days. If people are experiencing problems with anaerobic conditions they may be over watering.  
In our non wetting soil, the major advantage to wicking beds is being able to drop the hose going full bore  into a big pipe and go off and do something else for 5 minutes while it fills. You know the water is going right where your intended plant recipients are, and they are  going to get every drop. It is not going to grow weeds, the water isnt germinating weeds. 
  Anything that save us water and time is worthwhile in my book.


4 Comments Add yours

  1. Sara says:

    Hi! My name is Sara. My group and I from UCSD are doing a special wicking bed project in a marginalized neighborhood in Tijuana, Mexico. The soil there is very contaminated-some pathogens, organics, metals for sure. We are launching an experiment, together with the residents of the area, to make wicking beds in this very arid environment, that during the winters because of the topography and city planning, floods pretty badly. In the interest of using what's in the natural environment to make the gardens, we wanted to use pebbles from the original surrounding land. However, they are in the contaminated soil, and we don't want to waste water washing them. My question is: Are these pebbles going to be okay to use in our wicking bed reservoir without rinsing them???What if the water gets mirky?Thank you!!

  2. Merri Bee says:

    I think I answered your question by email but just as I don't see it here I will say again: Well Sara, first can I say “good on you” and very best wishes for it. Sounds ike very hard conditions and you are doing something great for the kids there. Is there any chance of chipping tree prunings? In Australia we are lucky to have machines that chop up tree branches and these woodchips are the ideal material to fill the reservoir. Failing that, I think you are going to have to “spend” the water washing them. You don't mention the substance /s that are contaminating the soil, but if it was me and I had enough water to contemplate starting a small garden, I would wash the toxic soil off the pebbles with some of it. I think you have to find clean soil to put in the top section too. By the action of HOT ( 60 degrees Celcius for a few weeks) composting, pesticide residues are miraculously neutralized. So if needs be, you can take waste from shops (like outside leaves of spayed vegetables etc they are throwing out), compost them carefully and use the resulting compost in the wicking bed. Worm castings however are another matter and can often contain heavy metals.

  3. Calexa says:

    I am trying to work out whether to put blue granite or scoria in my wicking bed. I am concerned about the leeching of heavy metals from rock. Is this a concern with either of these? There is not really anything to find about it on the web, but there is a lot of imformation about soil contamination around quarries. I note that plants (brassicas) are used to ‘mop up’ heavy metals from water near quarries and mines. Does anyone have any expert knowledge on this?

  4. Bee Winfield says:

    Your diligent research is commendable. I recommend using chunky wood chips , lighter and easier and no toxicity .

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