From making "miniature gardens" as a youngster, with a saucer, stones, flowers and using mirrors for ponds I progressed to using real plants and beautiful agate slices of all colours for the ponds.
Each pot or saucer is a "little world" which develops in the same way as the Japanese bonsai. The plants and trees adapt to their world and grow in much the same way as a full sized landscape. As in your proper garden weeds can grow so pull them out in the same way.
If the tree starts to go leggy you can pinch out the growing tip to make the shape you want.
Care: The garden can be kept inside or outside. It needs good light but not full sun in the heat of the day as it will dry out quickly. Spraying is good but does not replace watering properly.
It needs to be kept well watered but not overwatered. You soon work out the weight of your garden when it is just enough.
If it dries out the water can just run off and go down the sides. You need to plunge it in a bowl of water and leave until the bubbles stop and the water soaks in. Do not leave it in there for more than a couple of hours.