Gardening : Sex in the Greenhouse: New Plants From Old : Propagation: Raising plants from seeds or cuttings can be a rewarding, enjoyable hobby. It also allows you to grow rarer varieties.

Making new plants from old, or sex in the greenhouse--call it what you will, propagating your own plants is easy, fun and very rewarding.

If you think it’s a kick to coax a store-bought African violet back into bloom, imagine the joy of watching a plant you created from “scratch” burst forth with lush, gorgeous flowers.

Here are the basic methods of propagating houseplants:

Seeds: Although any plant that flowers can be started from seed--and that includes virtually every plant in the kingdom with the exception of ferns, which do not flower and are propagated from spores--this method is a bit more challenging than methods such as rooting cuttings or runners.

But the advantage is that you can grow some of the rarer plants that aren’t universally available in local nurseries and garden centers, lots of herbs you might want to try in your kitchen window, or perhaps the seeds and pits from citrus, papayas, tamarinds, mangoes and other exotic items from your grocery bag.

Once you’ve obtained your seeds, either from a nursery, through the mail or from your own plants, simply fill a tray or tray-like container with some rooting mixture--commercially available vermiculite is best--and dampen it. Sow the seeds about half-an-inch deep and an inch apart, place the tray in a bright, warm location, and make sure the soil never completely dries out.

When seedlings appear, which should be within about three weeks, separate the larger, stronger seedlings and put them into individual 3-inch-diameter pots in a mixture of half potting mix and half peat moss.

Cover each pot with a plastic baggie, keep the seedlings in a bright, warm spot, (but not direct, hot sun) and water as often as necessary to keep the soil slightly damp. Feed once a week with liquid houseplant food, and after about three more weeks, remove the plastic “greenhouse” and let the plantlets grow on their own.

Within four or five weeks the plants should be ready for transplanting into larger pots with regular potting mix.

As for growing ferns from spores: Spores are found on the back of certain fern fronds in masses of small, round, light circlets in precise design. Clip an entire frond and place it in a closed paper bag to ripen. As soon as the spores are ripe--they will dry out and turn a deep brown--shake them off and follow the directions for growing plants from seed.

Stem cuttings: Stem cuttings can be taken from practically any plant. The plants we most commonly propagate from stem cuttings include philodendron, pothos, ivy, arrowhead, Chinese evergreen, wandering Jew and Dracaena.

Select a stem that’s several inches long with four to six healthy leaves and cut off the stem from the parent plant, right above a leaf node, using sharp scissors or a single-edged razor blade. Plant the stem either in damp vermiculite or place it directly into a container of water.

The advantage of using vermiculite (which must be kept damp at all times) is that the resultant root system will be stronger than one that forms in water. Rooting your cuttings in water is more fun, though, because you can actually see the roots forming and growing. Kids particularly enjoy making stem cuttings, because in most cases they can be kept growing in water alone for up to and sometimes more than a year.

Leaf cuttings: This method is similar to planting stem cuttings, but only a leaf and about half an inch of its stem should be used. After taking your cutting, dip the leaf and stem into a rooting hormone to help prevent rot, then submerge the stem and the bottom third of the leaf in damp vermiculite. Keep the vermiculite damp, keep the cutting in a warm, bright spot, and new plantlets should appear from the base of the leaf in three or four weeks.

Plants that are propagated from leaf cuttings include African violets, certain succulents, geraniums and members of the Peperomia family.

Division: This process is best for ferns, cane-stemmed begonias, African violets and various succulents such as sansevieria--any plant with more than one stem emerging from the soil.

To divide a fern, for instance, into two or more plants, simply cut through the root system with a very sharp knife, then plant the sections into individual pots with fresh potting mix and a few drops of a vitamin B1 solution to help ward off shock.

Air-layering: This technique is a bit more complicated. It’s used on woody or thick-stemmed plants such as yuccas, Dieffenbachias, dracaenas or ficus plants. If your Dieffenbachia, for instance, has grown tall and leggy and you’d like to make two plants (or more) out of one, then air-layering is a good bet.

Pick a spot as far down or as near to the top of the plant as is aesthetically pleasing to you--but below the lowest leaves or leaf buds. This will be the base of your new plant.

Then, using a razor blade or sharp knife, cut a notch in the side of the trunk. Place a small piece of toothpick into the notch to keep it open, and wrap damp sphagnum moss around the notch, securing it in place with a plastic baggie or some plastic wrap.

Every two or three days, remove the plastic, spray the moss with water and then put the plastic back on. Within three or four weeks roots will have grown out from the notch in the trunk.

Now cut through the trunk about an inch below the rooted notch. Plant the part of the plant that you’ve removed in a 6-inch-diameter pot filled with fresh potting mix. The remaining stem can be cultivated as before--keeping the plant in a bright spot and watering it enough to keep the soil damp. Soon, two little shoots will emerge from either side of the stem and eventually form a new plant.

If the stem, or cane, that remains is too long, it can be cut into 6-inch long pieces then be individually rooted in vermiculite or water.

Stolons: Stolons, or runners, are small plantlets that dangle free from the mother plant. Most commonly seen on the spider plant, the strawberry geranium and the flame violet, these runners can be propagated by cutting them off just above the top of the plantlet and then potting them into individual containers.

Offsets: Small plants that appear at the base of an old stem are called offsets, or suckers--or in the case of many bromeliads, “pups.” To propagate an offset, simply cut it off the mother plant with a very sharp knife or razor blade, dip it in rooting hormone, and then pot it in potting mix. It’s best to wait until these offsets are somewhat mature before separating them from the parent plant.

Hybridizing: Only God can make a tree. But an adventurous plant person, with lots of patience and greenhouse conditions, can create new forms, especially with orchids and African violets. The science of hybridizing is very special, and if you’re interested in inventing new plants, you’ll find plenty of scientific literature to help you down this particular garden path.

Whatever plants you choose to propagate and whatever method you choose to use, watch what happens when you really get into propagation. You’ll find yourself trading cuttings with friends, giving cuttings as gifts and perhaps even trading cuttings through the mail. Happy growing.