I have been starting out my bonsai seeds for about a 6-7 months (I'd like to show I can do the trees basic needs before buying anything further in the process and don't mind the wait). I did about 60-100 hours of research before starting the investment. I have them placed in the windowsills of my sun room which gets an adequate amount of light with temperatures and conditions mirroring what is outside with a few degree difference weather or not I have the windows open. Different windows sills have different amounts of light/time.
As long as conditions are close enough to the outdoors these should be fine year round moving inside the trees that have hit their threshold as far as their temperature tolerance? I live in the Midwest United states where temperatures get to about 90-100 F max in the summer and on a extremely rough winter we have had up to -60 F in the winter (-20 F max on average winter). Any suggestions are greatly appreciated and would be more than happy to elaborate on any specifics. I have read I don't know how many posts of "Never grow inside. Ever" this seems to be in response to people growing in their living room though.

Thanks in advance for the input,

K.Suits

If you did research you will have seen that you do not have bonsai seed. Conditions inside will never be like outside.

Bonsai seed as in normal tree seed that will be made into a bonsai. Didn't know I needed to specify that.

Thank you for your insight.

Just forget the inside idea: many have tried, even more failed. Just take a look at the "help my tree is dying" questions here in this forum. 90% ( maybe even 99%) are because their tree is inside.

Time for more research, this time for your particular climate. Really the best thing is to find a local person or society and discuss with them what to do. Pay particular attention to those who have kept trees alive for a decade. Pay closer attention to those with similar trees to yours.

I think I would plan on this: when outside temps drop to below 25F or so I would move them into an unheated building like a garage or a shed. Close to a window facing the sun would be nice. Monitor the temps in the room and when they are dropping below 20 or so all day put a small heater in there to keep it above that. In the spring when temps are reliably above 25 bring them outside, unless they have started leafing out, and then wait for 32.

Pay more attention to local people who know your climate.

Your sunroom with just a few degrees warmer than outside is giving the same conditions as a coldframe or unheated greenhouse. In colder places the recomendation is to keep the tree sheltered during winter. I would consider your sunroom a sheltered place, not indoors. However, you might benefit from a fan circulating the air.

Hi, and welcome to the forum.

I see many responses, but what I miss is information on what you are growing?

Your sunroom is attached to the house and heated I suppose? I have seen some great examples of people in the US where they have a complete tropical climate in their sunroom to keep tropical bonsai over winter.

So please, tell a bit more, which species and what sort of conditions do you get in your sunroom?