Hey everyone, I tried to find a similar subject on the forum and didn’t find anything so hopefully I’m not rehashing something that has been said before, if so I apologize in advance and would love to see the thread.
I have around 8 little stone pines that germinated maybe 5 months ago and they are still in a tray with just some peat moss and I’m looking into transferring them to individual pots with a nice substrate so that they can develop and live happily for the next few years.
My question is if you guys use some special soil mix for your little seedlings and what would that be? From what I understand a fairly organic soil is the best for small developing seedlings but I would like to make sure I’m not missing something and if there are any soil mixes that could help them get strong. I imagine some small pumice would be great but given that we don’t really want to hold water having the organic soil maybe Lava would be better to allow for a better balance of water and oxygen but please correct me if I’m way out there.
Thank you and I hope you all have a great beginning of spring with all the trees waking up!
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Sorry, just realized I wrote Substarte instead of substrate on the title… not sure if I can change that?
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Idk about stone pine, but I’ve started japanese black pine in basically potting soil. Mix in a bit more perlite if you’d like ensure that it’s a bit more free draining. I’ve started Scott’s pine in potting soil as well. Not saying it’s the best or whatever. Just saying that I didn’t really even think about it much and it worked.
If I were to do this again, now that I’m more “technical” in my approach, I’d probably go with a mix of akadama, pumice, diatomaceous earth and pine bark. I’d actually be more concerned about the container. Going back to “what are you trying to accomplish” my goal would be developing root mass that isn’t circling on itself. My container of choice is a root maker pot. A pond basket if I don’t have one available.
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If youre looking for the fastest development, I would grow them out in a high quality potting soil like mix with a little extra perlite or pumice added to ensure good drainage. The nutrient exchange in this type of medium should provide faster development compared to trying to put it right into a bonsai like mix.
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This makes a lot of sense, I had not thought about the container but it is obviously a more important choice, I had never heard about the root maker pots but I’ll try to source some to my country if not I will go with the pond baskets as you mentioned and then I guess as @MaineBonsai mentioned nutrient exchange is critical for the fast development.
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I totally agree about the pots, I would just make sure I don’t go too big too quick. Starting small and up potting with most plants seems to be helpful in keeping a balance of water and oxygen. When I lose percolation, it gets root bound or dries out too quickly I transplant into a slightly larger pot. It sounds like you’re on the right track 
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I have had good root growth with a colander inside a similar or slightly larger colander. The drainage and oxygen available for root growth is excellent. When the roots start to pass through the holes into the lower colander, I rotate the upper one to prune the roots and encourage the small feeder roots that are confined in a relatively small space. The soil will determine how often you need to water. I use pumice with lots of organic fertilizers. The moisture level in the container is easily determined by lifting to see if it is light. The possibility of overwatering is very low with pumice. An organic potting soil mix can easily hold too much water. 
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This is kind of what I was thinking to do since its so hard to source specialized equipment here, colanders with a nice mix of pumice, a bit of organic soil and worm castings to have a very nutritional soil and a nice balance of water and oxygen. Do you put soil in both of the colander or just on the one on the inside and then the second as a mean to prune those roots coming through?
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I put the sifted soil into the top colander and used unsifted or the fines into the bottom to make a deeper water column and allow the roots to penetrate before pruning. This still allows air to be available to the roots and still have water remaining in the soil. Works fine for me. Using a heat bed or warm surface and keeping the air temperature cool or cold has given good results.
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