mycorrhizae in Gritty Mix?

g000n(9)April 12, 2012


Will mycorrhizae work/survive in Gritty Mix? From what I understand mycorrhizae require soil while the Gritty Mix is essentially a soiless mix.


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I would agree that a mix that contains some proportion of "soil" is going to provide a better environment than the gritty mix. That said, I don't think your mix is a critical as your fertility regimen. A bit of background on mycorrhizae.

Mycorrhizae are fungi that form a symbiotic relationship with plant roots. They help the plant to access certain nutrients (e.g. phosphorus) which are often present in the soil, but not in a form that the plant can use. My understanding is that, in return, the fungi feed on secretions from the plant roots. In circumstances where the plant has easy access to nutrients, the fungi enter a dormant state. The plant doesn't "need" their help and will provide no reciprocal benefit to the fungi. This would be common in a highly fertile soil or in a situation where the plant is being provided all the nutrients required for healthy growth. So, if you're following the Foliage Pro fertilize-with-every-irrigation routine, your plant is not likely to benefit from mycorrhizae. Ditto any situation where you are applying fertilizers which contain synthetic phosphorus, e.g. triple super phosphate, diammonium phosphate, etc. These are rock phosphates which have been processed so that they are immediately available for uptake by the plant. On the other hand, if you are using organic fertilizer or if you are growing on marginal soils, then mycorrhizae could very well provide a benefit.

IMO, mycorrhizae use has been over-hyped. I'm not saying that they aren't beneficial, I just don't think mycos are a cure-all that benefit any plant in any situation. Given their recent popularity, it's easy to forget that mycorrhizae have been around for many, many millions of years. If you read old soil science textbooks, mycorrhizae are commonly mentioned among the myriad soil microorganisms. Mentioned, as in, "Yes, these are among the fungi and bacteria that populate the soil." Now, marketers would have you believe that you have to add them to the soil - and not just once, you need to do it every year. That's where they start losing me.

I read posts by a lot of folks who are looking to tailor their growing medium and fertility practices to suit the mycos. Better to decide on the other factors first - growing mix, synthetic vs. organic fertility, etc. - then evaluate whether mycos are likely to improve your results.

    Bookmark   April 12, 2012 at 10:45PM
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Actually, fortyonenorth, I've read research articles that showed effective MF inoculation in bark-based soil-free media in nursery conditions.

g000n, a few of us are doing a bit of an experiment this summer, using MF in containerized pepper plants to see if there's a noticeable difference. I'll be using the 5:1:1 mix in some, and gritty mix in others. We'll be posting the results here.

    Bookmark   April 13, 2012 at 6:44AM
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Actually, fortyonenorth, I've read research articles that showed effective MF inoculation in bark-based soil-free media in nursery conditions.

No doubt. I'm just saying there are better options than the gritty mix if you want to make use of mycorrhizae. If your objective is to grow plants - not fungi - then it makes sense to optimize all facets of your production process. If mycos fit into your routine and will provide a clear benefit, by all means use them. If not, don't.

    Bookmark   April 13, 2012 at 9:06AM
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@fortyonenorth, I hear what you are saying. I plant fruit tree in Gritty to get fruit, not myco. Myco to me is just something that may improve the fruit tree so there is no need for me to adjust my container medium to favor myco.

@ssmdgardener, I can definitely see myco surviving in 5:1:1 since the primary ingredient is organic, so it will break down and provide the organics needed for its survival. I'll definitely be looking forward to your results from the Gritty Mix. Reason being is that the Gritty is made up primarily of inorganic matter.

In general, I understand that some of the nurseries are using soiless mixes that may be very compatible with myco because they contain a high percentage of ORGANIC material. The reason I posed the question originally was because Gritty Mix specifically is highly INORGANIC. I wondered if the inorganic nature of Gritty is completely non compatible with myco.

Thanks everyone for weighing in.

    Bookmark   April 13, 2012 at 1:26PM
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tapla (mid-MI z5b-6a)

Remember - compared to mineral soils (gardens/beds/topsoil) the gritty mix is very high in organics at 1/3 carbon-based fraction compared to somewhere around 1/20 or less in most mineral soils. I always see a lot of fungal presence in soils of temperate plants in spring when I repot w/o inoculating with anything.

Sorry the picture of a root mass after lifting it from the container isn't larger - not sure why.


    Bookmark   April 13, 2012 at 7:59PM
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"mycorrhizae use has been over-hyped"

Very true. In synthetic fertilizer programs they do not do much at all.

    Bookmark   April 14, 2012 at 2:31PM
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I've met organic farmers who use mycorrhizae (and/or rock dust) on the roots when transplanting, as a way to reduce shock to the plant. I don't know if this helps when using containers with Gritty Mix, although I've tried it.

I always get some leaf loss, more or less, depending on the plant and disturbance to the roots.


    Bookmark   April 28, 2012 at 2:31AM
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