Sep 182011

You know, I’ve been doing this horticulture thing for a while, and over that time, I’ve seen a number of garden designs, products and “innovations” come and go.  Remember the giant scoping rake hands?  What about the combination chilli sauce/garden pest spray?  Even the ever-popular “upside down tomato planter” has me scratching my head a little!  But every now and then I come across an inspired innovation, a dandy design that makes me excited to get out into the patch and give it a go.  One of these I’ve been convinced of this week is wicking beds, and I hoped you’re as interested in them as I am.  And they can be constructed on the soil in your garden or on hard surfaces in a courtyard and even using a polystyrene box.

What Is a Wicking Bed and Why Would I Want One?

So, what is a wicking bed?  Well, as I explained to a colleague of mine, it’s essentially a giant “self watering pot” in the form of a garden bed.  Okay, there is a fair bit more to it then that, but the idea is a garden bed designed to draw water up from a reservoir below, hence “wicking” through the soil directly to the roots.  A system devised by Australian engineer Colin Austin, wicking garden beds (and wicking worm beds) are gaining popularity as a wonderfully water wise garden bed alternative.

Drawing water from a reservoir below the growing medium, wicking beds operate on the concept of capillary action, with the soil and plant roots drawing this water upwards as required.  Essentially, this means that a properly constructed and maintained wicking bed should have nice, moist soil most of the time, with the roots accessing the water as they require it.

Wicking beds have a number of benefits, both environmentally and horticulturally.  Firstly, it’s a great set up for thirsty gardens (like vegie patches) in areas that have lower rainfall, or are affected by water restrictions.  Wicking beds also deliver the water were it’s needed (the plant roots), which minimises water wastage, and can also help to reduce the risk of funky fungal foliage issues.  Also, wicking beds are said to be more effective at sequestering atmospheric carbon than many other traditional types of garden bed set ups, meaning it’s a win for us, and the planet.

The Wicking Bed How To

So let’s look at the nuts and bolts of constructing a good, functioning wicking bed.  Essentially, it’s all about having the right depth, right medium (both for drainage and for growing you plants) and taking a bit of time to construct the bed properly.  It may sound tedious, but you will thank me in the long run.  So where do we start?

1. Choose a suitable site for your patch (full sun for vegies), ensuring that it is level (or you are able to level it) – wicking beds work best when they are level, as this ensures even water dispersal down the track.

2. The total depth of the patch may vary depending on what you wish to plant, but, for a wicking vegie bed, the overall depth needs, ideally, to be 600mm.  This equates to 300mm for the reservoir/water saturation zone and 300mm for the growing/root zone.  It should be noted here that wicking bed wizards all agree that water cannot be wicked further than 300mm, so bear this in mind when you are looking at preparing your patch.

It is possible to use polystyrene fruit/vegetable boxes e.g. broccoli boxes, for wicking beds.  In that case, the overall depth will be reduced.

3. Of the 300mm reservoir/saturation area, about half of this (150mm) will contain gravel or scoria (we prefer scoria since it holds water) and the water inlet pipe, while the other 150mm will contain a soil blend.  Prepare this area first.  If using a polystyrene box, omit the 150mm soil blend layer.

4. If you are gardening on soil, dig a hole to a depth of 150mm, ensuring it is level.  This will form the water reservoir. If you are placing your garden on a hard surface, ensure it is level and move to next step.

5.   Make the sides, so the bed has a total depth of 600mm, including the hole you just dug.   If using a polystyrene box it will, obviously,be less.  Line the entire bed with good quality builders plastic or pond liner, ensuring there are no tears or holes.  To prevent tears in the builder’s plastic, you may wish to add a shallow bed of sand to the base of the reservoir hole.

6. Now it’s time to put in the water delivery system.  To do this, place about an inch of scoria into the bed for the horizontal pipe to sit on. This will act to improve the drainage.  Then, install a length of 50mm wide PVC pipe vertically, attached to a PVC 90 degree elbow the will sit near the base of the bed on top of the scoria you have just placed.  Next, attach a length of 50mm slotted agricultural pipe (this has outlets holes in it) to the elbow, and this will run the length of the bed, along the centre.  Place a cap on the end of this agricultural pipe.

7. Cover the pipe and the bottom of the bed with scoria, to a depth of 150mm.  Cover the scoria with geotextile to prevent soil particles moving into the reservoir and blocking the pore spaces.  Shade cloth could be used but it will allow some soil to pass through to the reservoir.

8. Fill the next 150mm of the wicking bed with a good quality water retentive soil – this will form the “saturation layer” and is NOT where your vegies will be planted.  If using a polystyrene box, this layer is omitted.

9. At the top of this soil level (300mm), you will need to install an overflow – this will allow excess water to leave the wicking bed after significant irrigation events, or long periods of rain. If  using a polystyrene box, this overflow will be at the top of the reservoir i.e. at 150mm. One of the easiest ways to do this is to use a water tank tap outlet, and drill an appropriate size hole through the end of the wicking bed opposite the water inlet.  This is important, and may help prevent the soil in the root zone becoming waterlogged and useless.

10. Fill the remainder of the bed (another 300mm or so) with a good quality soil/compost blend.  We recommend 1/2 mushroom compost, 1/2 organic soil mix, as research and experience has shown that wicking beds work best with a higher than usual compost portion. DON”T use the soil from surrounding gardens, especially if it has a high clay content.  Mulch well with a straw based mulch (to about 5-7cm), taking care not to cover the PVC pipe opening.

11. Using a hose, and in accordance with local water restrictions, fill the wicking bed reservoir using the PVC pipe opening.  You may wish to use an old tomato stake or similar as a “dipstick” to see how deep the water is. Fill the reservoir to about 200mm.

12. Once the soil is damp (you may need to water from the top initially as well to encourage the wicking to begin), plant out your wicking bed with your favourite incredible edibles.

13. Sit back, water less, and enjoy your wicking bed and its harvest!

We know you may need a printout to take out into the patch and get constructing, so we have a PDF for you here!

How To Keep Your Wicking Bed Working

Like all things in the garden, the wicking bed is certainly NOT a no maintenance set-up, and, if left untended for a long period of time, could very easily turn into a sludgy, smelly, salty unproductive mess.  So, some things you may need to be aware of and monitor in your wicking bed over time are as follows:

  • Ensure the overflow/drainage hole or pipe does not become blocked or non-functional.  Give this a good clean out every few months.
  • Be aware that, as a closed system, everything you put into the bed stays in the bed.  Overuse of fertilisers (even some of our trusted organically derived ones) may see the soil sour fairly rapidly, leading to an increase in saltiness.  This is certainly NOT ideal for many of our productive vegies and herbs.
  • Greywater (that is, water from the bathroom and laundry) should NOT be used in a wicking bed at any time
  • Compost and soil mixture will need to be topped up seasonally, as will the mulch.  A good idea may be to lightly turn the top 300mm of growing area with a garden fork at this time, to “freshen up” the soil.
  • Cover the open end of the PVC pipe (the water inlet) with a tile, brick or similar.  This will prevent mosquito larvae from breeding in the tube or garden reservoir.
  • If you have used a polystyrene box you may need to renovate the bed since plant roots may have reached the top of the reservoir or actually penetrated.  Just remove the soil and check the geotextile and reservoir – it is not too difficult!


  25 Responses to “Wicking Beds”

  1. Scoria is the best filler for the reservoir because the stones have many holes/channels in them and this means that they hold and wick more water than gravel. However, there are a wide range of adaptations that people have adopted and the lower layer is sometimes filled with sand, gravel or even old clothes. We have even seen ideas where the lower layer is formed by just using something to hold the upper layer in place e.g. inverted milk crates or some sort of rigid plastic frame, and the lower layer is totally water – this would require keeping the reservoir totally full for water to come in contact with the base of the upper layer. We don’t know how effective these other systems are for both plant growth and water saving.

  2. Hi,
    I am planning two 2 x 0.6 metre wicker gardens and plan to lay a 250mm gravel bed but scoria is proving hard to buy in bulk as I need around 650 cubic metres. Could you suggest alternatives to scoria and advise any design changes I may need to make (I noted an earlier comment that bluestone will only wick up to 100mm), thanks in advance

  3. The top layer of soil is where the most biological activity is. The middle layer needs to be able to ‘wick’ and hold water for the plants with the top layer providing nutrients. There are no arbitrary rules, just guidelines from peoples experiences. In our article the middle layer is not as rich as the top layer mainly for economic reasons. If your wicking bed is not as high as we have suggested, you need to remember that plant roots will grow to about 30 cm deep and the soil to that depth should be rich in compost.

  4. There is no one perfect wicking bed structure. The important characteristics of wicking beds are having a reservoir below the soil, an inlet pipe and overflow pipe, and a soil layer for the plants to grow in. Colin Austin seems to use a system that is different from SGA’s suggesting that even compost can be in the reservoir and that plant roots should get into the reservoir. This means that over time soil will enter the reservoir too and there is the risk that it becomes a stinky mess if fragments of roots remain in the reservoir along with superfluous nutrients after the plants have been harvested. This would be a worse problem if compost was used since it gradually breaks down. This is especially likely since their system seems to rely on adding nutrients from their fish aquaculture into the reservoir.

    The wicking method that SGA is recommending has a layer of soil between the potential plant root zone and the top of the reservoir to try to avoid root penetration and a stinky mess. It uses scoria which is a light weight rock filled with many small holes where water can penetrate – it will not decay and provides a strong support for the soil layer above. It relies on slow release fertiliser – not liquid added to the reservoir – either as pellets or compost.

    The mulch Austin mentions is for the TOP of the bed to slow evaporative water loss from above and that is certainly a good addition.

    SGA has not compared the two systems in a rigorous way. Perhaps you could try both methods?

  5. I’m confused! Am now about to add the stones & soil to my wicking bed BUT according to Colin Austin it seems he adds something like sugar cane mulch over the slotted agi pipe and doesn’t use stones at all. He states that people have misunderstood how he made the wicking bed.
    The soil is added over the top of this, to mimic nature.
    He states that eventually the stones layer will be filled with roots and bits of soil. He incorporates a worm farm in the bed to keep the soil sweet.
    What is your experience? Stones or mulch? After all this planning and effort I’d hate to end up with a stinky wicking bed that doesn’t work properly.
    What is the best height for the bed? I can do 50cm or 60cm.

  6. Hi – we’re a bit puzzled about the middle layer of soil (“good quality water retentive soil”). Is it necessary for the middle layer to be different in composition from the top layer (“good quality soil/compost blend”)? Or is it for economic reasons (e.g. middle layer soil is less expensive than top layer)?

    Peter & Rebekah, Seattle, WA

  7. That might work – the critical point is avoid air bubbles!

  8. re “good quality soil”, please read the articles on this website about soil, especially So, yes you can used the soil/compost you suggest.

    You are right the middle layer will eventually have worms and nutrients, but so will the rest of the bed. The reservoir will have nutrients but no worms if geofabric has been used to separate the scoria from the upper layers.

    Other sorts of rock apart from scoria have many disadvantages i.e. they are denser and, therefore, make the whole bed heavier, and they are not porous, so there will not be as much water in the reservoir (scoria has many channels within it)

    If your bed is only 40 cm deep you will have difficulty with the layers – the bed we describe is 60cm deep which is important so that it give 30cm of soil above the middle layer and reservoir. Most vegetables will only have roots extending to a maximum depth of 30cm.

    Your suggestion of putting a hose in to maintain levels will only work if no air bubbles develop. I hope it has worked for you.

  9. Can I suggest for this type of problem, rather than ‘driving a stake through it’s evil heart’ to remove the water, that you put a hose into the water inlet so that the hose is a low a possible in the wicking bed.
    Then hold the end of the hose up in the air and fill the hose with water (to make sure there are NO AIR BUBBLES in the hose), then slowly lower the hose down to the ground level. The water should now run out and empty the water in the bed. Water seeks the same level.
    If the bed’s water level is lower than ground level, you will have to dig a hole to that level. Insert the hose into the bucket so you can empty the bucket, but don’t allow the hole to fill with water.

  10. Can you explain what type of soil you meant by ‘150mm of the wicking bed with a good quality water retentive soil’ you used above the scoria? Won’t this eventually be populated by worms and nutrients from the top layer?
    Could I just use a layer above the scoria of a good quality soil/compost blend. (You recommend 1/2 mushroom compost, 1/2 organic soil mix.)
    Can crushed blue metal be used instead of scoria?
    My bed will be total 40cm deep, so instead of puncturing a hole in the pond liner, I plan to put a large hose in the bottom of the water reservoir (inserted in a second short piece of agi pipe) then take the hose up over the side and back down to ground level into a container.
    This way the water in the container will be exactly the same level as water in the garden bed (water level and quality can be monitored) and will allow the bed to be completely drained if needed. It can also be used to back flush if there is any blockage. The normal inlet pipe allows for flushing as well.

  11. Crushed bluestone is commonly used in wicking beds and will wick up to about 100mm. The geo-textile acts as a damp mat that the soil will wick from. If 7mm crushed coffee rock is similar it should work as the crushed rock is inert.

  12. Unless the soil you used to make the wicking bed contained worms or you have purchased some commercially, there would not be any in the bed. Two articles on our website, written by one of our enthusiastic subscribers, described a bed which incorporates a worm farm and We have also seen systems where plastic garden pots have been sunk into the soil of the bed and used to place food scraps in. Worms are added and, because of the holes in the base of the pots, are free to migrate into the rest of the bed and spread their castings.

  13. Hi there

    Was wondering does your wicking bed have any life In it (worms) and what’s the best way to get the worms in your soil. And how do you add compost to the bed. Do you have to pull out some of the soil and add in the compost. So your soil is always nutrient rich.

    Thank you

  14. Just wondering if Perth hills coffee rock would do the job of scoria as I am trying to keep costs down

  15. There is no need to refill if you can see that the inlet pipe is half full. The pipe should have water in it to a level just above the interface between the soil and the supporting gravel/scoria. I hope you measured that when you constructed the bed. If not, maybe ensuring the pipe is always filled to a height of at least 20cm.

  16. Hi there. Thank you for the article.

    I recently built two wicking beds out of IBC tanks which I clad with corrugated iron and timber then filled up. They are going really well, veggies are very happy!

    I’m just wondering if anyone knows when I should refill the water reservoir. The bed with the tomatoes has dropped a fair bit but it is still nearly half full. Should I top it up now or wait until its completely empty.

    Thank you!


  17. Having a means of completely draining the bed is a good idea. There are many variations on constructing wicking beds – see the other articles on our website and
    There is no need to dig the bed in – the suggestion was just so that the material used for the sides could be reduced. You can really use any container which can be made leak proof and which can have an overflow hole in the side.

  18. I’d suggest that a second drain tap is installed at the VERY bottom of the sump. That way the unit can be drained fully as required (each year or so) to get rid of any sour water. I have 4 beds and all are constructed with this sump outlet and they work very well. Of course, doing that will require that the unit be installed on top of ground level (or be plumbed so it empties further downhill) rather than dug in below the soil surface as your diagram shows. I’m not sure why a dug-in bed is needed, was there a reason for this (apart from perhaps some temperature buffering?)

  19. Installing the overflow pipe just above the scoria layer is also fine if the wicking bed is quite shallow and the water will wick up the distance to where the roots of your plants reach. Many people use lined polystyrene fruit boxes which are only about 400mm high and the overflow should be just above the scoria.

    Agi pipe already has holes in it – that is why it is used for drainage. It sounds like you plant to use some other sort of pipe that does not have holes, so you definitely need to put holes in such a pipe.

  20. Hi there,

    Other wicking beds put the overflow pipe at the top of the layer of scoria/gravel. Is that ok too?

    Does the agi pipe need to have holes put into it so the water can come out??
    This is the only step that is confusing me…


  21. To sweeten the soil I would include charcoal in the gravel. For years I have been plant ferns etc in vases, with no drainage, anything in anything with no drainage at all. Old toilets which are just like a tiny wicking bed, is a favorite with parsley, mints etc, with gravel and charcole in the bottom. It will ever over water as the excess water goes out the S bend

  22. I do not use sand/gravel/scoria, I do not see the point of adding this non organic material when the water from rain over time will send nutrient rich water to the reservoir below anyway. If this water level is kept full you then can end up with a stinky mess.

    I believe the key is to let the water in reservoir dry out (not the soil, it is still moist, just not flooded). I originally used the excavated soil back in. At times this has been heavy clay and over time it improves as plant roots grow and rot. I then went down the sand route and now I’m back to putting the original soil/dirt back in.

  23. Thanks for your reply Rob Bob (can I call you Rob?),
    Strangely enough since I left the original message, one variety of my baby spinach plants have shot to flower (standing some 60cm high). The other variety, flat leaf parsley and shallots planted nearby have greened up and are growing strongly.

    My untrained observation is that, at least some of the problem is that I planted out with seeds instead of having some plants big enough to start sucking up that water and getting the whole system working.

    I imagine my Bokashi layer had something to do with it, but find this compost system easy and efficient so would love to think it could work in unison with my Permaculture no dig gardens, especially as my garden is quite depleted and in need of increased microbial activity. It’s a joy to just compost everything in the kitchen (including meat, bread, citrus peels and onions) with no sorting, no rotting scraps for vermin, etc. I used a range of buckets and bags to create Bokashi for all my garden needs. Small bags that can be popped in under trees and bushes when planting like slow release fertiliser; buckets of fermented scraps from which liquid fertiliser is tapped off regularly and watered into the garden; bucket of scraps which contain light cardboard and newspaper alive with efficient ‘good guy’ microbes to quickly turn a no dig garden into a thriving garden producing a high and healthy yield; food for my wormfarms (stand alone and in garden ones). If I need to leave Bokashi out of future wicking beds, I would be a bit disappointed, but would continue to use it for other purposes. If I can find ways to incorporate it, I will be all that much happier.
    I see what you are saying about the gravel layer. I will check my specs and pics; I think the gravel level is in line with, not above, the outlet pipes. Definitely something to think about.

    I hope that, with spring upon us, that I will be able to save my wicking bed by planting some larger plants to keep water cycling and thus maintain it’s freshness. My biggest fear was that this rotten water was not good for my plants when the whole idea of Bokashi and of Permaculture is the nourish and nurture the plants that provide our food.

    I’m feeling that there is hope and have spared the wicking beds life for now. The level has gone done some 15cm, so I will stir it up a bit and top with fresh mulch and try some new plantings.

    We live and learn (and learn, and learn). Thanks for your advice.

  24. Did you put in any soil above the reservoir Kerri ?? I think if there was a 100-150mm layer of soil it would act as a filter of sorts & catch some of the nutriment the sandwich method would still work great..
    I think you might have to dismantle or **sigh** stake its heart which would be sad as I know how much work goes into them.. I have had to do it to 3 large beds due to root intrusion..
    Another problem I have seen with some of the first barrels I wicked up & beds other people have made is that the reservoir was not overfilled with enough sand/gravel/scoria.. I like to have the drainage lower than the one shown in the description above with no soil sitting water as it can start up an anaerobic bacterial
    quagmire like the one I think you described.. It happened in our spice barrels but we were lucky enough to get a good harvest still.. Now I bring the sand level up to about 30-40mm above the drainage port/pipe so that soil/compost will never be sitting in water & the water still wicks up fine.. People also forget that roots travel down & we quite often find the reservoir section of the barrels filled with roots..
    Here is the wicking page from our blog if it helps..

  25. We recently built an amazing wicking bed (3metres long x 1 metre wide x 600mm high) with tiered gardens at the ends. We used full Permaculture layers (alfalfa, compost, manure, straw) and also included a Bokashi layer. We couldn’t afford plants so planted the bed up with seeds. They were up days early and all looked marvelous.

    However, within a matter of weeks the reservoir was a stinky mess. Nearly all the plants failed to thrive with some disappearing, but many are still there weeks later and have not progressed at all. Strangely two varietys of baby spinach have done fine, and are providing the only yield from the garden. Lettuce, spring onions, two varieties of broccoli, bok choy, chinese cabbage and yellow beetroots are in some kind of suspended animation.

    The bok choy is flowering at a height of about 1″ (2.5cm).

    We guess the leaching of nutrients into the water caused this. We were so disappointed after all the effort we had gone to. I fully expected leafy vegetables to thrive (though thought nutrient levels might be too high for root vegetables to do their best.

    Now we can’t think of a way to clear this other than to drive a stake through it’s evil heart (a lot of times)
    and remove the ability of the garden to hold water. What a shame. Any ideas?


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