Size of Training Pot

Purchased this Limber Pine from a tree farm. As you can see in the photo it is in a 1 gal. pot. I slipped it out of the pot to check the soil. It is extremely root bound and the soil is about 80% organic. It’s potting soil and has very poor drainage. I am going to introduce about 60% bonsai mix, trim back the roots and put it into a training pot for a couple of years to let it grow out a bit. It is 12 in high and 9 in wide. I cant seem to find info on the right size of pot. L X W X H. It will winter in my garage with my other trees. Stays at about - 5 C. Any sugestions would be great. Thanks, Mike

I like to keep pines in training containers that promote the rootball shape overall and allow for vigorous growth while in training. I prefer grow boxes and like the following dimensions. 11inch by 11 inch and overall 6 inches deep. This is rough guidelines. I have attached an example for reference.

The size of your box is close to a plastic pot i looked at in Walmart. 12 in wide X 10 in and 6 in deep. I am sure i have enough scraps of pine or spruce in the shop to make my own the same size. This would train the root ball to a rectagular shape for the pot i will finish this tree in. I am taking some direction from a book by Bonsai Today Masters Series- Pines. They recomend not replacing more than 50% of the soil the tree is growing in with Bonsai mix on the first transplant. Do you follow this rule. I have had bad luck doing bare root on the first transplant. Yes, i have killed trees!!!. Thank you. Mike

The 1/2 HBR method is very effective for pines and standard practice. I believe the key to repotting is taking the time to remove the old soil gently, limit the damage to healthy roots, remove old soil and dead roots. Straighten carefully and cut back judiciously, leaving side roots to flourish. Reducing the length of thicker roots and circling roots. Mist frequently the root ball and the tree when repotting. I prefer to use wooden chopsticks rather than metal root tools. Patience and practice.
As i consider my time valuable and the tree the most important consideration i am careful to choose the best repotting media i can for that tree. So i consider particle size, inorganic where possible and proper drainage. Even if it means drilling extra holes in a container. The better materials and more careful the approach the longer i can allow the tree to progress before repotting again. And the healthier it will be to work on in the meantime between repotting. And i always secure the tree carefully in the container after repotting to protect the new hair roots from damage through unwanted movement.

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Thank you for sharing your knowledge Frank. You can only get so much information from books and the interweb!!. This is my first Limber Pine. I live in Calgary, Alberta, Canada, a city of 1.3 million, with “No Bonsai Store”?? The Rocky Mountains are about an hour west.This species is very common in the wild here. To harvest a tree from nature can be tricky. Rules for Parks, Crown lands and private property are strict. The seed for this tree was harvested in the Crowsnest Pass, about 2 hours from here and started at a tree farm, three years ago, so it used to the climate which can be harsh. I have a good commercial soil mix ( red and black lava, haydite composted pine bark), screened and washed twice. I will add 25% akadama and some organics. I may come back to this if i need more info. Will update in the spring 2019. Thanks again. Mike

I lived in the Edmonton area for 37 years so i am familiar with your location. Best of luck.