CategoriesMonthly and Seasonal Growing My Garden Diary

BioAssay – midway point

Tonoli BioAssay, 6 November 2019

If you've been following my blog posts, Facebook feed and Instagram, you'll know that I had the misfortune of buying in bulk landscape supply mix called "Veggie Mix" which I am now, with the midway point results of my BioAssay, very confident was higher in levels of herbicides than my tomatoes, broad beans, peas, sunflowers and many other plants could handle.

Not fun at all if this, on a very tight budget, is your first season in your new acre homestead... when your dream of starting to become self sufficient and creating a teaching garden for the community, turns into a nightmare.

I set up this BioAssay in order to test my theory that the problem was indeed in the suspect mix of bought landscape supply compost and veggie mix. I am testing 15 different soils with 2 different bean seeds per pot - one an heirloom climbing dry bean called Flagg and the other a dwarf commercial bean called Banjo.

This is what they look like a few weeks in:

(hovering your mouse over the image will give a description)


Direct Comparison between Best and Worst"
Pot 1: Daltons Big Value Bagged Potting Mix"
Pot 2: Daltons Garden Time Vegetable Mix"

My thoughts on the above

  1. Not all beans in all pots germinated, but that's just probably "normal" germination rate issues, although I'd have thought to have a near 100% rate of germination.
    I had 1x Flagg bean (heritage) - the very tall growing one + 1x Dwarf Banjo bean (commercial) - the shorter growing one in all the pots
    It looks like it was mostly the dwarf beans that did not germinate when there was only one bean that came up.
  2. Not all the first leaves are open yet, so I can't draw full conclusions on all of the pots yet. This is only MIDWAY point of the BioAssay. I'm not contacting anyone or drawing any final conclusions for another week at least.
  3. Point 2 taken into consideration, there's a very definite and marked difference between the Daltons Mix and the Landscape Mix that I grew the tomatoes in (the photo showing direct comparison) This pretty much confirms my hypothesis that the landscape mix definitely had higher levels of herbicides than should be allowed for a "veggie mix" or garden compost.
  4. I noted that all the pots that contain landscape mix has deformities.
  5. I also noted that some pots I did not think would show herbicide damage, is not growing so well...
    • I was surprised at my Shrub Garden showing some curling too. While I have no idea what the previous owners did to the ornamental rhododendron and bulb garden that I call the "shrub garden", it was pretty clear of weeds when we moved in and was under a thick layer of pea straw mulch. It may be that they topped it up with compost from the same (most local) landscape yard, or the pea straw has herbicide too (might be a different type). Or at the worst, it may actually even be spray drift, although I can't find any correlation to that on other parts of the garden, and this is the furthest away from pasture/farmyards.
    • The Herb Garden also had me baffled, but then I remembered that I actually did top it up with a some soil from the trailer we got for the potager garden, so it too has a layer of suspect mix and should have been labelled Existing Herb Garden Soil + Landscape Supply Veggie Mix
    • The Lawn Soil I did not have lots of hope for as it is basically pure clay...
    • I was surprised at the poor germination and stunted growth of the beans in the Dalton's "Garden Time" Vegetable Mix. ????
    • I am very saddened by the existing soil in the big greenhouse having such atrocious results... could again be that previous owners used it for something else, sprayed it for weeds, didn't use it and sprayed it for weeds, or it was again topped up with suspect mix before we moved in... no answers, just speculation.
  6. The Horse Manure was from a contact who is pretty much a naturalist and does not even worm her horses and only lets them graze her own organically grown grounds. Am sure it was rich pure up, but the beans are doing okay. We'll see when final results come in.
  7. I've learnt that cactus mix is by far the best seed starting medium out! (LOL) And Daltons Seed Raising Mix coming in a close second with Yates Black Magic only coming in 3rd place because one bean did not germinate at all.



  1. HI Minette,
    thank you for your article on the Bioassay test. How absolutely unfortunate to have contaminated potting mix. I am so sorry to hear it!! There is a product that would neutralize it that is called Magic Botanic Liquid sold by Wally Richards now in Marton. If this link doesn’t work his website is Garden enterprises. I use MBL to stimulate germination and help seedlings transplant, plus in foliar sprays and on the ground to helps mineral uptake. It has many uses. I think it is liquid charcoal actually hence its ability to decontaminate. All the very best with sorting it all out. Warmest wishes Julia

  2. Just spoke to Scott at Daltons re contaminates. They are clean. They supply commercial growers. They cannot risk using contaminated waster materials. They use a small amount of peat but mostly use coconut husks as the basis of their composts and potting mixes. I’ll be only buying their stuff from now on – no matter what the price. They bulk supply too which could be useful to redo any contaminated beds. I also rang Living Earth – an old fav of mine – I knew the main guy a long time ago. Waste Management now own Living Earth. Waste Management have off shore owners and are looking to create a rubbish dump in the dome valley. The person I spoke to didn’t have any idea what I was talking about. They have recycling facilities all over Auckland for green waste. Nice idea but not for me. I will not be buying any of their products – no matter what the price.

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