When in the process do you use mycorrhiza?

[Babru]

I read a 2015 Telegraph gardening article by my favourite scientist, plant biologist Ken Thompson. He said an American study showed that initially plants whose roots were inoculated at planting did better, but after a couple of seasons there was no difference. Tests after this time showed that those planted without mycorrizae added had as much of it on their roots as those planted with it. It occurs naturally in soil, so eventually populates the roots naturally.

He suggests that if you were planting up beds in land that used to be an arable field, or planting in rubble, it might be a good idea (but lack of mycorrizae would be the least of your problems!)

He also said that the British Standards Institution doesn't think they work. "In its new recommendations for planting young trees (BS 8545:2014), it says: "Data from several independent trials demonstrate widely conflicting opinions as to their efficacy and therefore they should not be used as a matter of routine."

I'm glad to see that it is probably not necessary, as it's so expensive to buy. Seems a way of hoodwinking gardeners into parting with their cash. That said, I have some left that I bought before finding this article. I'm using it up on shrub and rose planting, but I won't be buying any more when it's finished.

[Babru]

I'm guessing that it could be quite useful if one heat sterilizes one's compost to remove slug eggs and viable seeds.

The Ken Thompson article also said "if you garden in a way that mycorrhizas don't like, for example too much digging, fungicides or fertiliser, adding more from a packet won't change that.

For plants that are going to spend a long time in a pot, in a sterile medium, it's possible that adding mycorrhizas may do some good."

So sounds like you're right about adding it to compost you've deliberately sterilised.

[Mr Bones]

Only bought it once, to bump up the cost of a purchase so it became eligible for free postage (so voted Never). After a few seasons of no-dig the plot's now full of it.

[Snoop Puss]

^Interesting.

I've never used it and never bought it, but I was thinking about getting some for some walnut cuttings I want to take.

[Penellype]

I've used it once, when it came as part of a tree planting kit that I got with my minarette fruit trees. It was cheaper to buy the whole kit than the bits of it that I really needed (pots, tree ties, stakes, compost etc). As I was planting in pots in compost consisting of coir blocks and a mixture of nutrients supplied with the trees, there did seem to be some point in adding the mycorrhiza.

Like many others on this thread I don't really see the point in adding something that is there already if you are planting in the soil. Using it for veg never crossed my mind - brassicas don't form a symbiotic relationship with it anyway.

[Scarlet]

^Interesting.

I've never used it and never bought it, but I was thinking about getting some for some walnut cuttings I want to take.

They sprout really easily from the nut? I had walnut seedlings everywhere.

[rary]

Never used it I find things grow well enough without an unnecessary added cost

[It never rains..it pours]

I did a little reading on this once and came across a scientific trial on pine saplings that showed about 10% better survival rate. So I have used it on all bare root trees. At £1 a time to try and protect £5 to £45 (cost range of the 10 bare root trees have planted), hopefully avoid replanting effort/cost and most importantly as Nickdub once said, you can never get a year lost back, it seems ok punt to me. I did try small trial on strawberries once, only because some left over, but vine weevil destroyed the results. Wouldn't use on anything cheap or on veggies

[quanglewangle]

I thought I should put my two pennyworth in, having started the poll.
Onions
I did a trial on onion sets a few years back. A tiny pinch in each dibbed hole. Two rows with RootGrow and two rows without. I invited folks from the local gardening club to blind-judge the difference a few weeks before they were fully ripe. They could tell at once which ones had been inoculated: almost all were significantly bigger. Now this was a long way from a proper trial: I knew which ones were which and could have unconsciously favored the treated ones.
Greenhouse beds
I make up compost for greenhouse beds from GPC, sterile topsoil, and sharp sand so this will have no native fungus in it. I coat the roots of e.g. melons and tomatoes before setting them out.
Aubergines in pots
Same as greenhouse beds, sterile compost so I use it when setting plants out into their pots.
Modules to pots
I take the "can't do any harm" view and coat very small amount around the roots as I pot-on from modules.
Cost
You really don't need much. A packet lasts a season and that includes non-veggie uses too.
BTW It goes much further if you grind it up in a pestle and mortar just before use although probably best not to breathe the dust.