do I need some good dirt?

I am sprouting some Sourwood trees. I tried collecting the seed from my little trees, but it rotted in our fall rains before it had a chance to ripen, so I bought some seeds on line . I have over a dozen seedlings, about 3 mm tall. I read on line that Sourwood may need it's own special mycorrhizal symbiont. Maybe that is why they grow so slowly here in the Pacific Northwest, they miss their partner. Does anyone know about this? If true, would getting a mailed package of soil from under a tree in a woods and spreading it around my established trees help them? I could see mixing in real Sourwood soil when I pot up my seedlings in a month or two might help. Anyone done anything like this?

I have killed many sourwoods in my attempts to get one to grow here.
Some maps show them being native here, but not all.
Most maps show they're native to Illinois, which is just a few miles away.
So it's frustrating that I can't get one to survive here.
I have given up. I have also heard about the mycorrhizal requirement,
which may be why I've been unsuccessful.
I have seen commercial products which either provide the mycorrhizae or
make your soil more conducive to forming mycorrhizal networks,
but I've never tried one of them. Good luck with your experiment.
I'll be interested to hear what you learn.

Hmmm, maybe you need some 'good dirt' too, from under a stand of Sourwoods just a few miles away. I can picture it now: " but officer, I wasn't really stealing from the National Forest, it's just a bag of Potting Soil... No, not that kind of Pot... when do I get my phone call?"
. I have doubts how a bag of commercial 'mycorrhizae' could actually help. Even if they had the specific kind for your particular plant (I believe they are generally species specific), it seems that being in a plastic bag in a hot train, hot truck, then stacked at Lowes for months would likely kill whatever started out in it. I seem to recall when I used to buy bean innoculant they made it up fresh every year. I had in mind getting some kind DGer to ship me a box of freshly dug soil from under a native stand of Sourwoods. I could maybe trade for it.

I agree with you about the debatable value of commercial mycorrhizae products,
which is why I've never bothered trying them.
But maybe a middle-of-the-night Illinois soil raid isn't such a bad idea!
Keep your eyes peeled for my mugshot in the news if things go amiss...

I couldn't help myself...

a spitting image ...

Actually the sourwood soil is a fabulous idea and here is why. Mycorrhizae can be plant specific as you mentioned. There are 10 or more mycorrhizae that are very common and even form multi species symbioses with some plants. Then there are the hundred or so species that are very specific to either certain plants or locations, minerals etc. A few things to know about mycorrhizae: They can only survive in the soil if there are living plant roots. I am not yet sure how long they can survive in a dormant state but believe it to be only a few months at best. Mycorrhizae require the sugars (liquid carbon) from the plant to function. You know that film like substance that you find throughout soil that has really good tilth? That's from the mycorrhizae, They are the best soil conditioners on the planet, even ahead of worms. So with all that said, if Sourwood has a specific mycorrhizae requirement then the only viable source would be established sourwood root zones. You need to actually get some fine root hairs or rootlets in the soil you gather so that you are sure to have the fungal partner and spores. The mycorrhizae must contact the roots of the plant you are introducing it to. It cannot move in the soil until it has a source of liquid carbon (plant sugars).
I hope this is helpful,
Lance

Oh great...a wanted poster that looks just like me. I resemble that statement MLM. And they'll likely want to look into my dirt theft history... that's another can of worms right there. ;)

Lance-Very helpful, thanks. I think overnight mail would get it here alive, and actually mixing it into the potting soil as I potted the seedlings on might work, as roots should grow fast into the new soil. They are now just starting their first true leaves, and are 1/4" tall, so should be ready to repot soon.

Mipii-I once met a man who told a hilarious tale of ending up jailed on a felony charge for violating Federal Wildlife Laws. He took his 4 year old to his favorite childhood fishing hole, to teach him to fish, with a kiddie 'Snoopy' fishing pole. He caught a Crappie. Oops Dad apparently is not allowed to touch the pole. You better not confess to worm theft, they belong to the Government...

Ha, ha MLM, one of those stories that's not so funny at the time, I bet. A felony...wow! You know, there used to be a day when Federal Government wasn't too big for their britches. Now they fund all kinds of untoward things using our Crappie money...from a snoopy fishing pole no less. It's like stealing candy from a baby.