Substrate is the thing most beginners get wrong, and it is the thing that quietly limits a tree for years afterwards. This calculator takes your location, how much watering you can realistically do, and the species you are potting, then gives you a mix to aim for using components you can actually buy in New Zealand.
Treat the result as a starting point rather than a recipe. Adjust for your own conditions, and if a mix is holding water too long or drying out too fast, change it and note what you did.