Have an old book for which you are not so sure that anyone would be interested to read it again? You should ask yourself is there better and more creative way to recycle it than this.
Here you can see the whole collection of unusual planters which are used to host different plants. As you can see, those planters used to be once books. This idea was promoted ba Gardenkultur of Italy and it shows us how it is easy to think more about the ecology and nature by properly recycling our garbage.
Those books seem to be perfect place for different plants and they are pretty easy to make: you just need to carve a little whole and to fill it with the soil and seed some plant there. This might be perfect for keeping your bonsai plant in it.