Windowsill gardening: how to grow your own petunias from seed

Bring a little spring into your life this week. Sow a packet of petunia seeds indoors. By following a few simple steps, you can grow strong, healthy plants that look as good as the ones you buy in May.

Start with sterile soil. This is important because regular garden soil carries fungus spores that thrive in the moist, warm environment. If the spores are not destroyed, you will have a fine crop of mold, but no petunias.

You can buy sterile soil at garden centers or the grocery store. Or you can sterilize your own by baking it in the oven at 200 degrees for 30 minutes. Don't let the temperature get any higher, and don't give it an extra few minutes ''just to make sure,'' or you'll kill helpful bacteria that live in the soil as well.

Now that you have the soil ready, find a container. A milk carton cut in half lengthwise is fine, and shallow aluminum pans that baked goods come in work well. Punch a few holes in the bottom so extra water can drain out. Water well and let it soak in.

With tiny seeds such as petunias, I scatter them over the surface by tearing a half-inch hole in the seed packet and tapping gently on the top while moving my hand slowly and evenly across the seedbed. You might like to practice this technique first, using an envelope and one-quarter teaspoon of salt. Do it several times on a dark-colored surface to see if the grains are well scattered.

After planting, set the container in a sunny window. Lightly cover the top with plastic wrap. Check occasionally to make sure the soil is still damp. It should be just moist, not soggy.

Seedlings will emerge in 10 to 14 days. As soon as you see them, take off the plastic wrap. Then keep them moist, but don't drown them. You can water from the bottom by setting the container in a shallow pan of water until the top appears wet, or you can lightly mist the seedlings with a fine spray. If you choose the second method, be sure you dampen more than just the surface of the soil.

Soon you will have lots of tiny green plants.

Now comes the hard part. You've got to get rid of some of them if you want the rest to grow big. If you can't bear to part with a single one - and I never can - carefully transplant the seedlings into other shallow containers.

Use a stick or sharpened pencil to separate them gently. Water well and put back in a sunny window.

Feed the seedlings once a week with Rapid-Gro or a similar fertilizer. Use two teaspoons per gallon of water, or follow the package directions.

In early May, set the young plants outdoors on a sunny porch or next to the house. If the weather gets too cold, bring them back inside at night. After a week or so of hardening off, you can set them out in the garden.

When buying petunia seeds, you will find hybrid varieties more expensive but well worth the extra price. Cascade, a grandiflora or large-flowered type, comes in a range of colors. The blooms live up to their names, cascading in masses from hanging baskets or window boxes. They are suitable for bedding, too.

Another grandiflora, Pink Magic, and its white or blue cousins, are outstanding for their early blooms. They continue to flower heavily right up to frost time in the fall. For something different, you might like to try orange-hued Tangerine or Sunburst, a yellow.

Multiflora petunias have smaller blooms, but there are lots of them, and they stand up well in unfavorable weather. Commanche, a scarlet red, and Coral Satin, a deep salmon, are both All-America winners. Sugar Plum is an especially sweet little purple variety. White Joy and its variously colored relatives are also good choices.

Finally, there are the double varieties. Most of them are a little slower to bloom and not quite as compact, but still showy for pots on the patio.

Apple, Cherry, Peach, and Snowberry Tarts look as delectable as they sound, but for showing off, you may want to try a few of the new double grandifloras. Circus, a reddish salmon and white bicolor, and Blushing Maid, a soft salmon pink, are both All-America selections of this type.

Once you have tried petunias, you can start ageratum, snapdragons, impatiens, coleus, salvia, and asters, using the same method.