I have two lovely junipers that I purchased from my local nursery last year with the intention of turning them in to bonsai. I know that they would benefit from a less restrictive growing condition for a few years rather than putting them straight into conventional bonsai pots right away. I don't have a garden to plant them in so my plan is to construct two grow boxes (or should I call them training pots?) from some old untreated timber I have lying around.

My question is this: what size of pot should I construct? From what I've read, the training pot shouldn't be much more than 2" larger than the current 10" pots. Does that sound about right?

How can we tell you what size what pot you need, if you don't tell us what size of juniper you have?

See pic...

10" pots with pretty well established roots. Tough to see exactly how big the trunks are but probably between 1-1/4" - 1-3/4" diameter.

Well I'm somehow unable to attach a picture to the forum .....





Hopefully the trunk and pot size are sufficient for someone to offer advise.

if they were mine, I would build 18" x 18" boxes that are 8" - 10" deep and let them grow for a couple years. I have an 8 year old juniper that has a 3/4" trunk and I'll probably do the same once I get more space to do so.
This is only my opinion.

Thanks for your input, simplysaid!

I'm a little constrained by space so I may not go as large as 18"x18" - but I'll certainly consider making the boxes larger than I originally designed.

well.. if you would only go for 12" x 12" i don't see the point in doing so..

I didn't say I was going 12"x12" so I don't know why you'd assume that...

that you wouldn't go as large as 18*18
to get any advantage if planting in the garden isn't an option, i'd go for at least 15*15