My Samanea saman reached the heigh I want, how do I make it stop growing? Do I cut the center leaf that is always growing? BTW its only three months old. Also if someone speaks spanish that would be great! My english is a little rusty

Hola, Salomon284, yo hablo Español, pero este sitio (forum) es en Inglês.
Why don't you post a picture of your tree so we can see what can be done? You say it's 3 months old, so it's a seedling, not a tree, right?

Salomon284 wrote: My Samanea saman reached the heigh I want, how do I make it stop growing? Do I cut the center leaf that is always growing? BTW its only three months old. Also if someone speaks spanish that would be great! My english is a little rusty

FYI: there is a Spanish version of this website (bonsaiempire.es).

You do not want it to stop growing. Trees that do not grow, die.
Probably you do not want to prune it yet either. It may be the right height, but if you cut it now, the trunk will stay thin too.

Salomon284 wrote: My Samanea saman reached the heigh I want, how do I make it stop growing? Do I cut the center leaf that is always growing? BTW its only three months old. Also if someone speaks spanish that would be great! My english is a little rusty

Usually we worry about the thickness of the trunk first. Once we achieve a good trunk thickness, we decide what the height of the tree should be depending on the trunk's thickness and style. Focus on trunk thickness first and decide what style you want your tree in the future. For example, if you want it to be upright, you want to make sure the trunk grows upright before it gets to thick. If you want cascade, you can wire it while it is still young and you can bend it. Once you achieve trunk thickness you decide the height, grow a new leader and develop primary branches. Then secondary branches. Then you develop ramification.

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Usualmente nos preocupamos por el grosor del tronco primero. Una vez que logramos adquirir el grosor deseado, nos preocupamos por la altura del arbol, la cual depende del estilo del Bonsai y el grosor del tronco. Por ejemplo, si quereis un estilo de cascada, debes asegurarte que el tronco crezca en modo cascada, asi que lo doblas con cable mientras es joven y facil de doblar. Una vez que el tronco adquiere el grosor necesario eliges cual sera la altura del Bonsai y creceras un nuevo lider y las ramas principales. Luego trabajaras en las ramas secundarios, y finalizaras con ramificacion.

I want it to be just like the real tree. I'll leave a picture of how it looks like right now. It's height is around the 30cm and is perfect for what I want.

But the trunk is still too thin, isn't it?

www.growingbonsai.net/growing-bonsai/growing-trunks/

Salomon284 wrote: I want it to be just like the real tree. I'll leave a picture of how it looks like right now. It's height is around the 30cm and is perfect for what I want.

Then you need to listen to the advise. With leaves this size, you 're going to need a couple of years of growth to get a decent trunk.
Else it will stay a stick with leaves.