Petunias are so easy and commonplace that even the most avid gardeners take them for granted, but they have much to recommend them besides their easy growing nature.
Petunias are readily available in six-packs or seeds in the spring and come in nearly every shade of color except yellow. There are even some fancy double varieties that have a more complex blossom than the familiar trumpet shape.
Petunias generally grow about 15 inches tall, but a newer type called “wave” petunias or “spreading” petunias are only about six inches tall, but spread so rapidly that they cover a huge area by fall, six feet in diameter, provided they are watered and fertilized frequently. This makes them ideal for tumbling down a terraced hillside garden. They are also beautiful in containers, where they hang two to three feet on each side. When grown in full sunlight, they are so covered by flowers that you hardly see any foliage.
Petunias can even survive very light frosts and potted plants can grow inside provided they get several hours of direct sun. They will need considerable trimming by spring as the stems get overly long. Garden petunias sometimes drop their seeds and you may get a few “volunteer” plants the next spring. They are perennials in climates where it never freezes.
Petunias look the best in masses of plantings of all the same color. With care, watering, fertilizing, and occasional trimming, they bloom all season. Give them some liquid fertilizer or manure tea about once a month.
Most gardeners buy them as six packs to start the spring with some quick color. Petunias can be started from seed, but it takes a long while. They may prove difficult for beginning gardeners to start indoors. The advantages of starting petunias inside are that you have a wider choice of varieties from which to choose, and you can raise large quantities of plants for less money. However, it takes ten to twelve weeks before petunias are big enough to transplant, so they need to be started early, January of February.
Because of their small size, petunia seeds can be difficult to work with. Not only are they very tiny, but they also need light in order to germinate. Pelleted seeds, seeds coated with little balls of starter fertilizer, are easier to handle, but are not always available.
Spread seeds sparingly on top of a container of sterile, damp potting soil. Water the seeds with a fine mist to wash them into the potting medium or press them in gently with your fingers before watering. Then cover the container with clear plastic to hold in moisture and store it in a bright, warm (70 to 85 degrees F) place–out of direct sunlight–until seeds begin to sprout. This usually takes seven to ten days after planting. Remove the plastic when seedlings emerge.
When seedlings are three or four inches tall, it is time to transplant them into individual peat pots or packs that hold several plants each. Feed them every two weeks (weekly for wave petunias) with diluted liquid fertilizer. Harden off young plants by putting them outside on sunny, warm days. Then bring them back in at night for several days before planting them outdoors.
Wait until the soil warms and frost danger has passed before transplanting petunias. Keep removing old spent blooms to encourage new flowers and prevent the plant from producing seeds. Petunias attract butterflies and bees.
Petunias face relatively few diseases. They are so inexpensive it is often best just to pull out and replace any that look infected. Insects such as aphids and slugs sometimes attack petunia. Wash with insecticidal soap for aphids. Trap slugs by placing pots upside down next to the plants. The slugs will take refuge under them in the day and can be easily disposed of.
Another problem is harsh weather. Wind and heavy rain can make the large petunia flowers look beaten down and bedraggled. Trim damaged and overlong stems to keep the petunia fuller. The plants will grow out and look great again