Similar to many other hobbies you may uptake, the amount you’ll need to spend to practice growing bonsai trees depends on your level of involvement. For example, if you grow a single bonsai plant and keep your tool kit at a basic level, then practicing bonsai won’t be extremely expensive. However, the more plants you grow and the more tools you decide you need, the more your costs will rise. You’ll also need to consider the cost of basic indoor gardening materials, including containers, soil, fertilizer, and more.