Anaerobic wicking beds - a cautionary tale

A Forum for discussion of ideas and techniques for gardening practices that encourage biodiversity and minimise the adverse impact on the environment through such things as reduced water use, organic pest control and wildlife friendly practices.
Includes Environmental Weeds sub-forum

Moderators: Forum_mod, Pam, jack, Sam, Lea

Anaerobic wicking beds - a cautionary tale

Postby Drewberg » Thu Jul 14, 2016 12:48 pm

My partner and I recently built some wicking beds. After much research into different designs we decided to build them using the less commonly used "media-less" design. This means that instead of using scoria, rocks or something else in the reservoir, our reservoirs are just empty holes. The beds are raised beds 600mm high, with pond liner inside to form the waterproof reservoir. Then we have plastic bread trays stacked two high (30cm) and wrapped in geotextile. A layer of geotextile over the top of the bread trays separates the soil from the reservoir. A drainage hole is drilled through the bed wall at about 30cm (top of the reservoir). About 25cm of soil is on top.

We completed two beds in this way about 5 weeks ago and planted a mixture of seedlings and seeds. In our enthusiasm to test the system we filled the reservoirs (despite it being Melbourne winter). Since then growth has been very slow. At first I put this down to winter and late planting, but I soon realised that plants were looking quite miserable and something must be wrong. I discovered a couple of weeks ago that the water in the reservoirs had gone anaerobic - stinky, black, disgusting. I think the reason for this is that the drainage hole is placed a little too high. With the reservoir full the geotextile is always in contact with water, making the bottom of the soil go bad. We've had a lot of rain this winter so far which hasn't helped. The soil has never had a chance to dry out.

Upon recognising the problem I went about flushing out the reservoir as best I could. I also then siphoned water out. I couldn't get it all out but have lowered the water level a lot. I'm hoping that this can be a short term fix. We've also added in-bed worm towers (in 100mm PVC piping) to the beds. Over time the worms should help aerate the soil to prevent it going anaerobic. I hope the good microbes in the worm juice and castings will also help. I read somewhere that putting some bokashi liquid into the beds could also help, but I'm not sure if I should pour it into the reservoir or onto the soil. Any ideas?

I'm a bit concerned that the soil has just become very compacted from all the moisture and will only recover if I give it a good digging to aerate it. However this would mean digging out all the plants, which I'm loathe to do!

The long term solution (that I want to put off until spring planting) is to dig out the soil and drill a new drainage hole 50mm lower down. This will reduce the reservoir capacity but will stop the soil getting drenched, and ensure that rainwater always has somewhere to drain to.

We built a third bed a few weeks after the first two using much the same design. However we didn't put any water in its reservoir, so we're hoping it will be okay. However, some of the seedlings in it seem a bit unwell - yellow leaves on broccoli and bok choy. The soil is a veggie mix from our local soil supplier and seems pretty good (recommended by a friend) so I'm sure it should have all the necessary nutrients. PH tests have found it to be neutral.

I wanted to post this partly as a cautionary tale but also in the hope that people might have suggestions for short term remedies, so any comments are appreciated. I'm still confident that the beds will work well in summer but I don't hold out much hope for my winter crops doing well this year.
Drewberg
Lawn trimmer
 
Posts: 5
Joined: Fri Jul 01, 2016 10:55 am
Location: Melbourne

Re: Anaerobic wicking beds - a cautionary tale

Postby karyn » Mon Aug 01, 2016 10:14 pm

I made 6 wicking beds last year, in the more traditional style, and I put the sdrains in too low, so they dried out too fast. So I blocked them with silicon, and started to make higher ones but got distracted. I agree, sodden wicking beds are putrid, stinky, vile things!!
User avatar
karyn
Gardening Sage
 
Posts: 1828
Joined: Tue May 08, 2007 12:48 pm
Location: Adelaide Hills

Re: Anaerobic wicking beds - a cautionary tale

Postby Drewberg » Tue Aug 02, 2016 11:16 am

I made 6 wicking beds last year, in the more traditional style, and I put the sdrains in too low, so they dried out too fast. So I blocked them with silicon, and started to make higher ones but got distracted. I agree, sodden wicking beds are putrid, stinky, vile things!!


So they never got their new drainage holes? Yuck, they must be a putrid mess! Do you have a plan for rehabilitating the yucky soil? Will you need to replace it altogether?

An update on my progress: Witnessing the poor growth and yellowing leaves of seedlings in the newest bed (the one that hasn't gone anaerobic), I came to the conclusion that the soil mix was nutrient deficient. Seems to have lots of composted wood bits, lots of sand, but not much if any nitrogen rich organic material. A couple of weeks ago I gave a top dressing with blood and bone, a feed of seasol and dug in some manure where I could. Suddenly things have started looking healthier and are putting on some growth!

We've had lots more rain in Melbourne so on the weekend I again siphoned water out of the two anaerobic beds. It wasn't as stinky as before but still a bit yuck. I'm tempted to leave the drainage holes where they are (as I'm sure it will be fine over summer) and just try to keep the water levels from getting to0 high in future winters (normally wouldn't be hard but this winter has been very wet).
Drewberg
Lawn trimmer
 
Posts: 5
Joined: Fri Jul 01, 2016 10:55 am
Location: Melbourne

Re: Anaerobic wicking beds - a cautionary tale

Postby markgrogan » Mon May 01, 2017 11:34 am

When wicker beds are the topic of discussion, the main concern should be the method of storing them. Without a proper drainage system that includes the size of it, the level, and ventilation, the whole setup could become a complete waste of time which produces a mess. Thanks for sharing your progress updates so we can take some references for a better setup.
Mark Grogan @ http://supercheapselfstorage.com.au/facilities/storage-wollongong/
User avatar
markgrogan
Pruner
 
Posts: 19
Joined: Wed Dec 17, 2014 4:15 pm
Location: Wollongong

Re: Anaerobic wicking beds - a cautionary tale

Postby karyn » Mon May 08, 2017 8:45 am

My very delayed reply!
I siliconed up the old drainage holes, and used lengths of hose to sit on top of the geo fabric and then poke through the plastic lower down, therefore using a gravity drain. So far, so good. I've just top dressed them with some compost, and we'll see how well they drain this Winter. They've been excellent all Summer, but you absolutely have to get the drain in the right place! The putrid stinky water is really good for the garden!
User avatar
karyn
Gardening Sage
 
Posts: 1828
Joined: Tue May 08, 2007 12:48 pm
Location: Adelaide Hills


Return to Sustainable Gardening

Who is online

Users browsing this forum: No registered users and 2 guests

cron