Root division is actually the splitting or cutting up of one plant into two or more parts.

For a while you'll have small plants, but these divisions grow just as any normal plant and eventually become larger.  Almost any plant that grows from several stems in one pot can be divided; this includes pileas, peperomias, most of the ferns, aspidistras, and marantas.

To divide a plant, gently knock it out of its container; you may have to run a sharp knife around the edge of the pot to loosen the soil.  Remove the rootball and shake off as much soil as you can.  Then gently break the rootball apart to see how the roots are growing and to determine the way to divide it.

For example, airplane plants actually put out new stems and plants next to the original plant, similar to a sucker or offset.  These plants can be separated and potted up individually.  The roots of the sprengeri asparagus fern, on the other hand, simply build on each other to make one large rootball.  In cases like this, you'll have to cut the plant apart.  Don't be afraid to use your knife; it's actually better to cleanly sever their roots than to tear them into pieces.  Sometimes asparagus ferns have so many roots you simply have to cut some off and discard them.

Put the divisions into smaller pots.  Water thoroughly, and set in indirect light for a week or two while the plant adjusts to life on its own.  Early spring is the best time to divide plants.

Bulbs also are propagated by root division.  The amaryllis and oxalis form offsets that can be cut from the parent plant and potted up individually.  Propagate before new growth starts in the spring.

The tuberous begonia and caladium can be propagated by dividing their tubers into two or more parts and potting them separately.  Spring is the best time for dividing.

The gloxinia and cyclamen will grow from the "eyes" of their tubers, just as a potato plant grows from eyes.  Cut the tuber while dormant so that each piece has an eye, and pot the pieces individually.