I have been looking at the use of recycled tractor tyres in gardens after someone mentioned that you couldn't use them for raised bed vegie gardening. Given the increased interest in backyard vegie gardening (sometimes with limited space) I thought there was good reason why one should know one way or the other.
To date every gardener I have spoken to has had a different opinion but no-one can tell me 'why' or 'why not'. Where can we find the definitive why/why not?
The information I found on the internet was inconclusive at best, some nineteenth-hand anecdotal and therefore sometimes confused/confusing. I am reeling from a morning of Chinese whispers on the subject.
So I couldn't help but think about bringing a spot of science into the equation and providing a definitive answer. We have several sustainability experts at the Otago Poly and a big pool of brainy boxes at the university who could help with the qualitative data side of things. We could go national and get a tab from John Key to use DSIR or whatever it is called these days. It would be a fabulous collaborative project for Poly, Uni, Council and Community, NZ! I can see the ODT headlines already "Save the vegies - save the world".
The main answers I am looking for are:
-how evil are used/recycled rubber tyres ? - there is agreement about what nasties go into tyre production, off-gassing of new tyres, toxic products of burning tyres, bio-contamination of "shredded" tyres with hugely increased surface area (as used in weed/playground mats) but what measurements are available of degradation products leaching into soil where they are used for home grown vegies?
ie WHAT does leach into the soil and is it absorbed into the food chain?
- so following on can they be used in vegie gardens or only for ornamental?
- can you use them for some vegies and not others? (root/leafy/fruiting)
- small or large - does size make a difference?
- radial or normal (tyres)?
- drainage? does moisture affect the oxidation/degradation of the rubber? does sufficient drainage assist in any way? (for those placing tyres on concrete bases)
- do different fertilizer regimes have any chemical affect on tyre stability?
- if excess zinc is leached into the soil - is it having a disastrous effect on vegetable growth
- assuming there is leaching and absorption would lining the inner cavity with 120 plastic polythene remedy this situation?
- what do the worms think about all this? A popular method for making worm farms is to use a stack of recycled tyres stuffed with newspaper from which the run off is collected and used as fertiliser - presumably this is "bad" also (if the tyres are degrading and bio-toxic leachate is being generated?)
As an aside - tanalised timbers are often used in raised bed construction. These are also manufactured using some very toxic chemicals. Does leaching occur when these materials are used? Given the recent scenario about inadequate drying of timbers and chemicals still being 'active' when used, do these timbers also raise a problem?
What wood is used in the 'pre-fab' compost bins for sale at Mitre 10 and other outlets. If it is tanalised why is it ok to use it for compost but we don't use tanalised sawdust for mulch? Is there a collollary here between potential toxicity due to increased surface area.
- what other recylced containers are people using for soil containment? Do these pose any risks? eg potting mix bags - what kind of plastic are they made of (these usually have phthalates in them too - are they stable in a polythene -type polymer plastic)
Final thought:
Perhaps it has been done already. If you know the answers to these WHAT and WHY questions I would appreciate if you could find the time to send me the references/links.
-
Me myself and I commenting - I have received some comments via email to stay away from using tyres in any part of the garden as they leach cadmium and not to use treated timber as leachates include cadmium, copper and
arsenic.
And another comment that some leachate comes off the tyres into soil, water etc etc but it's so miniscule it is not really worth worrying about.
And again I am asking, show me the numbers, as there are groups of people I know of advocating the use of tyres, and this concerns me if there is a potential for harm and they will need more than "say so" to think otherwise.
- Pam McKinlay - April 27, 2009 1:31 AM
-
Show me the numbers indeed! I read somewhere about treated timber.. I think it was research linked from the Wikipedia entry, that quantities were so small as to not be a concern. Different soils drew out different amounts, but nothing on a scale near threatening to humans.
That said, I wonder if the quantities are enough to have an impact on micro organisms which are essential to healthy soils? - April 27, 2009 4:13 PM
-
Hi. I have heard a rumour and it is just that, though I do have a neighbour who could confirm it for me, that Mitre 10 staff have been told to advise customers to use untreated timber for garden boxing. We use untreated timber in our garden and believe it will last a good couple of years. It's cheaper and not a big deal to replace.
It's not just the danger to us and any micro organisms in our environment that we need to think about. We need to think about the fact that the nasty polluting goes on in the process of tanalising timber, someone has to be involved in this process and buying it creates more demand for it. As always, it's bigger than just us and our vege patch.
I too would like to see some research (has any actually been done?) on the topic. :) - April 27, 2009 8:52 PM
-
Hi Pam,
You have got me thinking now. I have been successfully growing courgettes in tyres over the summer and eating them, the courgettes didn't seem to suffer, however I don't know about the longer term effects on my health or the health of the soil etc. I also have a very healthy worm farm in some old tyres, the worms are thriving and so are all the other micro-organisms involved. I would have thought that if there were toxic leachates from the tyres the worms would suffer and fail to thrive. This is not the case. - April 28, 2009 4:26 PM
-
worm farms in tyres! excellent idea!
- April 28, 2009 8:31 PM
-
I have been receiving many replies via email and I am going to summarise a couple of new points here as I will lose track of them in my mailboxes (but I completely understand if people are nervous about commenting in the blog, keep those messages coming).
One respondent has raised the issue of the toxicity of decking timber in relation to infant health and safety ref: Plunket Safety Update magazine.
Another is recommending we legislate tyres under product stewardship priority products in a submission on the Waste Minimisation Act 2008.
http://www.mfe.govt.nz/issues/waste/consultation.html
Please add your voice in this submission.
But back to my original question. I now have a stack of reports to read through, none of which are completely relevant, but I shall see what I can extrapolate from them and then see if I can answer my questions which I think are still relevant and write them up in a new post.
As I am studying, working, caring and mothering this will be my g-job. "g" for Gaia hypothesis maybe, just as well it is winter as it won't need to be "g" for gardening! but at least one of my colleagues will be amazed that I have tended lovingly to my blog three times this week. - April 29, 2009 3:19 PM
-
Hi Helen and Leigh,
I used to have a tyre worm farm but changed to straight out composting (I run a three bin system like my Dad used to) which the worms were happily rehoused in. But I agree the worms seemed to thrive in the tyres (in size and number).
I got the design for the worm farm from Alice McKenzie, "Wastebusters" in Ashburton - they run a great educational recycling outfit at the dump. They have a HUGE worm farm there and can give you fascinating details about what tiger worms will and can't eat.
Ah yes, me again. I do have a literature search in progress and am intending to provide some answers to my questions, but in the meantime I asked a chap from Delta who is a scientist and engineer about this and he said that tyres were no longer used in stop-bank structures because of the leachate into ground water and on that basis he assumed they would be bad in gardens. And the reason that tanalised timbers had lost favour with grape growers had more to do with the nature of the soil grapes are grown in. The leaching from the timber itself was pretty localised but grapes are grown in porous soil substrates and the leachate goes straight down to the root stock. If I don't get back here before you do try the Ministry for the Environment (NZ), "tyre tracks" project, for further info.
ReplyDelete