House plants overgrown? Divide the root balls

''Stop it! Stop it!'' you command your pot-bound strawberry geranium.

''Please don't grow any more,'' you plead with your snake plant. ''The windowsill can't hold a larger pot.''

Often, in the limited space of modern quarters, success with house plants produces a special problem. There comes a time when you run out of room fit for plants.

Yet, your plants continue to advance and expand until one day you spy evidence of their need for larger pots. Roots grow out of drainage holes; plants start rising out of their pots; they wilt and turn yellow and, in general, seem to lack luster.

You can, of course, donate overgrown plants to family or friends with larger quarters. Or, you can move to ever-larger homes. However, in the case of the many house plants with more than one stem growing out the soil - cast-iron plants, African violets, clivias, and most begonias, ferns, and geraniums - you can divide the foliage and root balls.

The result: two or more smaller plants in place of a single large one.

There are two schools of plant division. The first calls for a clean, swift cut with a sharp knife through foliage, soil, and root ball with no hesitation in the mid-roots. The second opts for gentle separation of the roots and foliage , using fingers or a pointed stick.

Keep in mind that if the root ball is extremely tangled, the fast cut will result in less root damage than a long period of pulls and tugs.

In both instances first remove the pot-bound plant from its container by turning it upside down and tapping along the rims and sides. Choose your division method and separate the foliage and root ball into two or more parts. (Each part should have a main stem.)

Dislodge any drainage material lodged in the roots and remove as much of the old soil as possible without injuring the roots.

Plant each part in a separate container. First, place a layer of drainage material at the container's bottom. Then, while suspending the plant over the drainage material, with one hand fill in with soil to within an inch of the rim. With the other hand, settle the soil by lightly tapping the pot on a solid surface.

Firm the top soil about the plant's stem(s) with your fingers. Water thoroughly.

Keep the newly potted plants in the shade for a couple of days before placing them in their permanent locations.

The start of a plant's growing period, which usually occurs in the spring, is the best time for dividing it. However, it can be done any time, especially when you're in need of a fast and free gift.

Here are some candidates for division:

* Rattail cactus (Aporocactus flagelliformis).

* Asparagus fern (Asparagus plumosus).

* Sander's calathea (Calathea Sanderiana).

* Peanut cactus (Chamaecereus silvestrii).

* Purple velvet plant (Gynura aurantiaca).

* Baby's tears (Helxine soleirolii).

* Prayer plant (Maranta leuconeura Kerchoveana).

* Boston fern (Nephrolepis exaltata bostoniensis).

* Marble queen or Pothos (Scindapsus aureus).

* Coral beads (Sedum stahlii).

* Starfish flower (Stapelia variegata).

* Wandering Jew (Tradescantia zebrina).