The petunia can make a beautiful addition to the sunny garden. They range in height from 12 to 15 inches tall and come in a large variety of single and bicolor plants. Their bright shades of blue, purple, pink, white, red and yellow will bloom all summer.
Petunias make wonderful bedding plants and when planted in large numbers provide a delicious, unforgettable fragrance. They can be used for borders and in mass plantings in the garden. They are also wonderful for use in a hanging basket, patio container, or window box where they will cascade down with a tidal wave of color. Although mostly used as annuals, petunias are considered a tender perennial and can be used as houseplants in a sunny window or in a greenhouse in the winter.
Petunias are classified as either multiflora, meaning they produce many small flowers, or grandiflora, meaning they produce fewer, larger flowers that can be as large as 5 inches wide. Both types are available in single and double form.
Petunias need full sun and well-drained soil to do their best. You must dead head them for continuous bloom. To do this simply pinch off the flowers that are past their prime. They prefer to be kept on the dry side and can get droopy in rainy weather. Rain can also be responsible for petunias to get a fungal disease known as botrytis, which causes dark spotting on their blooms. The multiflora varieties are the most rain tolerant and better at resisting this disease.
Petunias can be started from seed outside but they take a long time to germinate and so it is recommended that you start them indoors 10 to 12 weeks before the last frost in your area. The seeds are tiny and need plenty of light to germinate.
The best way to start petunia seeds is to scatter them, evenly, over the surface of your planting medium in a small flower pot or seed starting box. Press the seeds lightly into the surface but do not cover them. Use a misting bottle to thoroughly wet the surface. Keep them moist by covering your container with clear plastic until the seedlings begin to appear. Once they sprout, remove the plastic for a few hours a day, for several days, and continue to keep the planting medium moist. Seedlings need 12 to 16 hours of sun each day so you may want to use florescent lighting if yours aren’t getting enough natural light.
When the seedlings have developed two real leaves (don’t count the first ones that appear after sprouting) you can thin out the seedlings to avoid overcrowding of the plants. Overcrowded plants will be weak and leggy and have poor air circulation leading to disease.
You should always thin out seedlings by cutting the smallest or unhealthiest looking ones with a scissor at the soil level. If you pull them out, you can disturb the root growth of the seedlings that you wish to continue growing. Leave at least one inch between remaining plants.
Petunia seedlings can be transplanted to larger containers when they have at least four real leaves. Do not disturb the root system while transplanting. Carefully dig around them with a spoon and lift them out. Replace them into the larger container of moistened planting medium. Keep the repotted plants in bright sunlight and well moistened. Apply a liquid fertilizer once a week at half the regular strength until the plants have at least six real leaves.
Before finally transplanting your petunias outside you will need to harden them off. (The gradual acclimation of indoor plants to outdoor conditions) To harden them off you need to bring your seedlings, in their containers, outside during the daylight and place them in a sheltered area, away from wind and direct sunlight around the time of the last frost date. For the first couple days, three hours should be enough time. After that, five hours for a couple days is recommended. If the plants are doing well, you can move them to a sunny spot and leave them out day and night. After the last frost date in your area, feel free to transplant them directly into the garden.
You can always skip the entire seed process and purchase plants at your local gardening center where they have a large variety of petunias to choose from.
To plant petunias outdoors, use a trowel to dig a hole one and a half size as wide as your potted petunia. The plant should be placed in the ground at the same depth that it was already growing. Refill the hole with the soil you dug out of the ground and tap the soil to firm it around your petunia. Scatter compost or fertilizer around the plant. Never put fertilizer directly into the hole with your plant as it can burn the roots. When you have finished planting all your petunias, add a layer of mulch to the garden to help control weeds and keep your soil moist. Be careful not to over water as they prefer to remain a bit dry.
At the end of July if you cut back your petunia plants to about 6 inches and feed them some fertilizer, they will come back in a few weeks and continue blooming up until the first frost.