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Re: The perils of bought potting compost

Posted: Wed Apr 19, 2017 11:02 pm
by Weedo
The pics Odsox posted don't look like herbicide damage to me - certainly not hormone type products (phenoxy's) or Glyphosate. While not discounting some of the other herbicide types, I would be very surprised if you could get seeds to germinate in the contamination levels were this high.. The interveinal chlorosis and necrosis seem more typical of severe nutrient deficiency, most likely Iron and Manganese (but could be more complex) Mushroom compost is almost all organic and "spent" material is normally very nutrient poor, at least for green things. I suspect that as the plant grew and you fed them, the problem lessened?

Personally, I would never buy compost from recycled garden waste or use spent mushroom compost as anything but an organic bulker with other materials.

Re: The perils of bought potting compost

Posted: Thu Apr 20, 2017 7:53 am
by Odsox
Weedo wrote: I suspect that as the plant grew and you fed them, the problem lessened?

No, feeding did nothing and most of the plants died.
I don't agree that it was "severe nutrient deficiency" as all the plants were only a week or two old and were grown in seed compost with fertiliser added (by the manufacturer)
I've been growing my veg plants exactly the same way for umpteen years and last year was no different. So from when Adam was a lad up to 2014 I had no problems, 2015 slight problems, 2016 sever problems, 2nd sowing in 2015 with different compost and 2017, no problems whatsoever.
I would think that points to something untoward with the media rather than cultural ?

Re: The perils of bought potting compost

Posted: Thu Apr 20, 2017 10:48 pm
by Weedo
OK
Part of my job has been investigating claims of off target herbicide damage on crops - I have never seen this type of damage as a result of herbicide overspray or contamination but will investigate other possible products further. Unfortunately there is no chance of a soil analysis.

Any ideas of what the culprit may be - potentially different products and usages in your patch compared to mine.

Re: The perils of bought potting compost

Posted: Thu Apr 20, 2017 11:54 pm
by Weedo
A couple of questions if I may re potential herbicide damage
are the plants being grown indoors and with heat?
has any additional nitrogenous fertiliser been used?
are Triazones (not Triazines) still in common use in your patch?

Re: The perils of bought potting compost

Posted: Fri Apr 21, 2017 2:48 pm
by Odsox
Weedo wrote:A couple of questions if I may re potential herbicide damage
are the plants being grown indoors and with heat?
has any additional nitrogenous fertiliser been used?
are Triazones (not Triazines) still in common use in your patch?


OK, I grow just about everything under cover, except maincrop potatoes and peas. The most affected plants were my tomatoes which were grown in 3 different locations; greenhouse, polytunnel and conservatory. No heat was used since taking out of my heated propagator immediately after germination.
I grow the tomatoes the same way every year, pot up using commercial potting compost and then some potted on in bigger pots and the rest planted out in the soil beds. I never feed until the first truss has pea sized fruit and then I feed once a week, but the damage seen in the photos was long before that stage.
I live on a very narrow peninsula and what farming there is consists entirely of traditional cattle out in small 1-2 acre fields.
The only application on the fields is an occasional lime dusting and an annual scattering of a general grass fertiliser.

As a comparison, here is a photo of my this year's conservatory tomatoes, in exactly the same spot as last year, grown exactly the same way I've grown them other years, except using a different potting compost.

Toms.jpg
Toms.jpg (159.39 KiB) Viewed 1242 times

Re: The perils of bought potting compost

Posted: Tue Apr 25, 2017 10:58 pm
by Weedo
Thanks Odsox, I think I know the culprit (at least the 2 chemical groups it would belong to) and it is a medium term residua that would remain in untreated green materials. I was a little thrown by the term "compost" as I would have expected the heat processes to breack most of it down - if the term is applied to "potting mix" it would contain both compost and other less treated materials that are more likely to retain the residuals.

Re: The perils of bought potting compost

Posted: Wed Apr 26, 2017 7:59 am
by Odsox
Weedo wrote: I was a little thrown by the term "compost"

Thanks Weedo, yes the term "compost" is very ambiguous here, but it has always been like that.
When I first started gardening, commercial seed compost was nothing more than sterilised sieved soil with added Levingtons fertilizer. Most dedicated gardeners made their own by stacking some turf upside down to rot in a corner somewhere and sieving that.
Then in the '60s it was gradually replaced with peat based, which is/was pretty much just pure peat with added fertilizer and a wetting agent. So up until this century seed and potting "compost" had absolutely nothing to do with composting.
Now that it's ecologically frowned upon to use peat, the commercial companies use either a percentage of, or pure, composted waste from a variety of sources, some good but some from very dubious sources.
Once it was easy, reliable and relatively cheap to buy seed and potting "media", but now (at least for the moment) it seems to be a case of horticultural Russian roulette.

.... I know, I really should be making my own. :iconbiggrin:

Re: The perils of bought potting compost

Posted: Wed Apr 26, 2017 11:04 pm
by Weedo
Yes, cross border terminology can be confusing. We have Australian Standards (AS3743-2003) for potting mixes which defines the physical and chemical characteristics of the material - while compliance is voluntary, virtually all reputable suppliers meet and label according to the standards. Generally, recycled, composted green waste is not used in commercial potting mixes but is used as soil, soil builders / additives etc. Often this is available free to rate-payers from council facilities. I have used some of this BUT stored is for a few months to "mature" before putting it in the garden beds.

Re: The perils of bought potting compost

Posted: Thu Apr 27, 2017 8:13 am
by Flo
Trouble is with green waste here, all sorts of things can end up in the skip to be processed. Japanese knot weed, mare's tail, treated lawn clippings to name but three that I have heard of going "to the tip". There are times when people don't think that a bonfire might be a better disposal method. Often due to ignorance of the fact that seeds and chemicals may not rot down in the composting process and be handed on to others.

Re: The perils of bought potting compost

Posted: Thu Apr 27, 2017 11:43 am
by Green Aura
Not to mention the shredded plastic that regularly fills it out too.

Re: The perils of bought potting compost

Posted: Fri Apr 28, 2017 1:39 am
by Weedo
Not much different here except that we are quickly moving to increase standards and processes for green waste management. We have just put the brakes on a proposal for a huge commercial green waste composting facility Nth of Sydney until they develop and we approve a weed management procedure to remove risk of weed spread while moving raw material to the site, invasion at the site and viable propagules in the finished product.