Pre-bonsai Development - Soil Composition + Pot Progression

[Hermes33]

I have several black pines, california/shimpaku junipers, trident maples, chinese quince, oaks and japanese maples I am going to be moving from bonsai pots they were sent in into 1-3 gallon nursery pots to allow them to grow larger more quickly. What soil should I use in these grow pots? I use the typical 1/3 akadama, 1/3 pumice, 1/3 lava rock for my bonsai in bonsai pots. Should I add fir bark to the pre-bonsai nursery pots? Is there any special way in which I should add the soil to encourage proper root growth? (ie I got one chinese quince that had styrofoam peanuts in the deeper parts of the pot and solid lava rock directly under the trunk). The effect was that there was more limited root growth just below the trunk which allowed them to move more laterally. In general, when is it good to use fir bark and can I use standard fast draining potting soil in pre-bonsai nursery pots?

Secondly, what are the benefits of various types of pot progression. I've seen some that keep their bonsai in smaller nursery pots longer and when can I start the transition to the 1 gallon --> 3 gallon ---> 5 gallon progression. These are for longer term trees I am trunk developing.

 

[Hermes33]

To add to this, any advice on cutting soil/grow pot size/time progression would be very helpful.

 

[LuZiKui]

Quite a bit on this topic on the site if you search around a bit. I always recommend watching some of Eric Schrader's Bonsaify videos on Youtube. He's a fan of a perlite/coco coir mix and has done some testing to show what growing medium produces the most growth for trees still in development. It would probably answer a lot of your questions. And you can absolutely use the 1/3 Pumice/Akadama/Lava mix in your bonsai containers but that will get pricey real quick!

As for the growing container topic I think the biggest issues is watering. If you plant a small tree (like a 3" nursery container) into a massive 10 gallon pot, it can be difficult to water it so it's not soaking wet on the bottom and dry on the top. In addition the roots won't be pulling much water out so it can add an additional challenge. The benefit of only up-potting in small increments is you can control the watering better. In addition most people don't have the space or resources to put every little tree in a 10 gallon pot so it makes sense to only go up as much as you need.

 

[Srt8madness]

Must be a millionaire to put APL in nursery cans 🫣
Make your own coarse substrate. If you can find a 50lb bag of pine bark chunks you'll have a great start. Sand, manure or compost or coir, perlite. Research each tree to see what they like.

 

[Hermes33]

Quite a bit on this topic on the site if you search around a bit. I always recommend watching some of Eric Schrader's Bonsaify videos on Youtube. He's a fan of a perlite/coco coir mix and has done some testing to show what growing medium produces the most growth for trees still in development. It would probably answer a lot of your questions. And you can absolutely use the 1/3 Pumice/Akadama/Lava mix in your bonsai containers but that will get pricey real quick!

As for the growing container topic I think the biggest issues is watering. If you plant a small tree (like a 3" nursery container) into a massive 10 gallon pot, it can be difficult to water it so it's not soaking wet on the bottom and dry on the top. In addition the roots won't be pulling much water out so it can add an additional challenge. The benefit of only up-potting in small increments is you can control the watering better. In addition most people don't have the space or resources to put every little tree in a 10 gallon pot so it makes sense to only go up as much as you need.

Yes thank you for info, I actually just found some other good threads… will remove this one.