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[RabidSquirrel]

Hi, this Japanese Black Pine was yellow when I received it. I expected it to die but over the past 3 months it greened up and actually grew a half inch. I have it in a tiny terra cotta pot I had lying around. The roots are starting to come out the bottom. I want to turn it into a bonsai. But, how old does the tree need to be? If I need to repot it, how big of a pot should I use?
I can't put my tree outside cause it's freaking cold in ND during the winter.

 

[Shibui]

There are no real answers to your questions or maybe that should be there are too many different answers to your questions.
There is no particular age that a tree needs to be for bonsai. Some trees are developed slowly over decades, some a grown much faster in the ground and progress much faster. Small pots generally restrict growth and slow all the processes.
When to begin bonsai training also depends what you ultimately want your bonsai to look like. Some people are happy with a little trunk in a pot. Many of us refer to that as 'stick in a pot' bonsai or 'mallsai'. Most experienced growers prefer to have bonsai that look more like trees with branches and a real trunk. That takes far longer to achieve.

Generally increase pots by one or 2 sizes at the most when potting up because excess space in a pot can cause problems. Many bonsai are developed in the same pot for the entire process. Every few years we cut some of the roots so there is space for more to grow.
I have no concept of how cold ND winter is but Black pine is quite cold hardy. You'd need to talk with some experienced growers from your area to see how they manage winters. Pines really don't do well inside long term.

 

[penumbra]

Shibui gave you an excellent answer to your inquiry in all ways but I would like to reinforce one thing. A black pine is going to die for certain if you keep it inside.

 

[sorce]

@RabidSquirrel ?

Welcome to Crazy!

My JBP seedlings did -24* just on the ground.

Sorce

 

[Leo in N E Illinois]

@RabidSquirrel
A tree's horticultural requirements do not change when you take them out of the ground and grow them in a pot. So a tropical tree will require a warm winter. A temperate tree will require a cold winter rest.

North Dakota can be pretty darn cold. Your warmest zone is USDA 5, and at elevation your coldest can be USDA zone 3b or 4a. Frostbite Falls, North Dakota is not entirely a joke.

Japanese Black Pine, Pinus thunbergii, JBP, is a pine that ranges from the sub-tropical areas of Japan north through the coastal areas of Japan. In northern Japan the coastal areas are still pretty warm, USDA zone 6. Japanese black pine are not reliably winter hardy much north of Saint Louis Missouri. If you are regularly colder than Saint Louis, you probably need to protect your JBP in winter.

Japanese black pine do need a cold winter rest to set the new buds for the next years growth. They also grow poorly indoors on windowsills, and will grow less than compact under high tech light systems. Even under 1000 watt high pressure sodium lamps, in a high tech light set up the growth of my own JBP was lanky, elongated and not the desired growth needed for bonsai.

I winter my JBP in an unheated well house. They stay dormant the whole winter. I bring them out after danger of hard frost in spring. The well house stays between 29 F and 40 F all winter.

You will need to find a spot for your tree where the temperature stays below 40 F. for the entire winter. I know this sounds complicated, but often an unheated garage will work. You want the coldest the tree experiences to be above about 23 F.

 

[RabidSquirrel]

Thank you for your reply. We usually drop into the -40° F for several weeks and it will remain a -20° for several months. That's without factoring in the wind chill. The latest frost is in the middle of May.
Do the trees need light while being wintered?

 

[leatherback]

Thank you for your reply. We usually drop into the -40° F for several weeks and it will remain a -20° for several months. That's without factoring in the wind chill. The latest frost is in the middle of May.
Do the trees need light while being wintered?

🌨🌨🌨❄🌬

 

[leatherback]

Do the trees need light while being wintered?

If kept at or just above freezing, no.

 

[MrWunderful]

Damn thats cold

 

[Leo in N E Illinois]

Thank you for your reply. We usually drop into the -40° F for several weeks and it will remain a -20° for several months. That's without factoring in the wind chill. The latest frost is in the middle of May.
Do the trees need light while being wintered?

@leatherback is right. If your tree is kept below 40 F, or 4 C for the winter, there is no need for light. There is zero light in my well house. I have no trouble wintering JBP and evergreen azaleas. The problem comes when your winter location gets above 40F before it is safe to put them outside. Do your best to avoid this problem. Or you will get locked into the "in and out dance". where you put the tree outside while its above freezing, and back indoors to avoid the night time freezes.