Because there is a limited amount of compost with a limited amount of minerals. In the garden there is loads of soil and loads of minerals. because of decomposition and absorption minerals can easily be replaced in the garden soil, unlike in a plant pot.
Answer:
The set of input values is called the domain.
....Do you mean What can be used to make a black hole? thats easy a black marker and a dark blue marker. :P or blue and black pens