Knowing how to grow petunias can make your garden more colorful with flowers that continue to bloom throughout the season. As a plant that has a variety of flower colors, petunias are very suitable to be planted as bed plants, garden dividers, in window boxes, and other containers. Varieties of petunias that stick out are also very suitable to be planted in hanging pots.
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Part 1 of 4: Start Planting Petunias
Step 1. Determine your petunia type
While there are hundreds of petunias to choose from, they are usually grouped into four broad groups, based on flower size and growing conditions. Some types of petunias are better suited to growing in pots, while others are better suited to be planted directly in the garden.
- Grandiflora has the largest flowers and is the most commonly grown petunia. Some types of petunias in this group have single petals, while others have double petals. Grandiflora also consists of varieties that stick out and grow upright.
- Petunia multiflora has smaller flowers but with thick, colorful petals.
- Petunia milliflora grows near the ground and has small flowers. This plant is easy to control its growth, so it is very suitable to be planted as a border crop.
- Petunias that grow creeping, spreading and extending above the ground (from a window box, for example) can immediately cover a large garden surface. This type of petunia should be watered more often.
Step 2. Choose your petunia flower
Once you've decided on the type you want, you'll still have to choose the petunia plant. There are several things you should consider when choosing the best bed plants.
For bedside plants, choose tight petunias (not tall and long-stemmed ones) because these types of petunias will grow better
Step 3. Determine the right place to plant it
All types of petunias need five to six hours of full sun each day, although they can still grow in slightly shaded areas. The soil should have good drainage, although it doesn't have to be particularly nutrient-rich.
Petunias grow well in pots, as well as in the garden. However, if you're growing it in a pot, you'll want to make sure to use a soilless growing medium (soilless media consists of peat, pine trunk compost, or coir, as well as inorganic materials such as sand)
Step 4. Prepare the soil for planting
Be sure to dig in rich, loose soil (so it has good drainage). You will also need to prepare and fertilize the soil so that it is ready for petunia planting. If you are growing petunias in a garden, prepare the soil by providing organic matter such as peat, composted leaves or animal manure. You should incorporate these organic materials into the soil until they are about 5-7.5 cm thick.
- Insert organic matter into the soil using a garden rake to a depth of about 20-25 cm. It can also help remove lumps of clay for better soil drainage, while increasing the ability of sandy soil to retain nutrients and moisture.
- Fertilize your soil with a balanced fertilizer (such as 8-8-8, 10-10-10, or 12-12-12). You need to provide fertilizer in a ratio of about 0.9 kg for every 9 square meters. As the seasons change (early to mid-July), you will need to apply a special liquid fertilizer to maintain flowering plants every three weeks (or once a week for creeping petunias).
- Now if you are growing your petunias in a window box, or pot, you will need to apply a slow-release fertilizer into the soil.
Step 5. Put proper spacing between petunias
Most petunias need at least 30.5 cm between plants in full sun. If you plant it in a shaded place, then close the distance between the petunias (about 22.5-25 cm). However, there are a few exceptions you should keep in mind:
- Petunia milliflora can be planted closer together up to about 10-15 cm, compared to other types of petunias.
- On the other hand, creeping petunias should be planted as far apart as 0.5 m from each other.
Step 6. Plant petunias in the right season
You should start planting petunia beds in early spring to help them acclimate to the outdoor conditions. If you plant petunias in the ground, be sure to wait until the threat of frost has passed (or you can cover them at night to protect them from snow).
- You need a soil temperature of around 16 degrees Celsius. If you plant them in lower temperatures, your petunias will not bloom.
- If the temperature is very hot, be sure to shade the petunia plant. Although this plant likes and can grow well in the sun, temperatures that are too hot can interfere with its growth.
Part 2 of 4: Growing Petunias from Seeds
Step 1. Start sowing petunias
Petunias are not easy to grow from seedlings, but they can be done, and mean you can grow more petunias for less! Begin sowing petunia seeds 10 to 12 weeks before planting (early spring is the recommended time, as in March in the Northern Hemisphere).
Try to buy seeds in pellet form, as these are easier to handle, especially for inexperienced cultivators. Petunia seeds can be difficult to handle, as they are very small, so be sure to take this into account
Step 2. Prepare the seeds for sprouting
Petunia seeds need special conditions in order to germinate. This plant needs warm, sunny conditions (with temperatures around 21-29 degrees Celsius) indoors, as it is not ready to be planted outside.
- Sprinkle the small seeds onto a damp potting medium or sphagnum moss. Be sure to leave some space between them so they don't crowd each other as they start to grow.
- Press the seeds into the potting medium or gently spray water to blend with the potting media.
- Cover with clear plastic and place in a warm and sunny place away from direct sunlight until it begins to sprout (usually takes between seven and ten days after planting).
Step 3. Take care of the newly sprouted plants
When the plant begins to sprout, remove the plastic cover. Move to a cool, sunny place after the plant sprouts. This process usually takes between 7-10 days after you have planted your petunia seeds.
Move to a cooler, sunny location after the plant has germinated. The best temperature is around 17 degrees Celsius during the day, with night temperatures between 12-18 degrees Celsius
Step 4. Place the petunia under a fluorescent lamp
You should place the petunia at least 10-15 cm under the lamp. Be sure to turn on the lights with a timer so you can ensure the petunias are illuminated for 16-18 hours each day.
- Elevate the lamp as the plant grows, so that the distance between the lamp and the petunia plant remains 10-15 cm.
- You don't need expensive plant-based lights. You can also use a regular fluorescent lamp.
- Make sure that your plant is located directly under the light (unlike before sprouting, when you need to keep the plant out of direct sunlight).
Step 5. Move the plants
You can move plants that already have three true leaves. Plant them in separate peat pots, or plant several plants in the same pot.
- Apply liquid fertilizer until the threat of frost has passed and you can plant it outdoors.
- Be sure to plant in moderately fertile soil with good drainage.
Step 6. Care for young petunia plants
You can do this by placing young petunias outdoors during warm, sunny days. When it gets cold outside at night, bring the young petunias back inside, so they stay warm.
After doing this for a few days, you can permanently grow your petunias outdoors
Part 3 of 4: Caring for a Blooming Petunia
Step 1. Stimulate the growth of new plants
Depending on the type of petunia you are planting, you will need to trim and pluck the tips of the plants to promote new plant growth and side root flowering. This step will spur the growth of new flowers.
- For grandiflora and multiflora, when the height has reached about 15 cm, pluck the tip to stimulate the formation of side root flowers quickly.
- Do not pick petunias milliflora or creeping petunias.
- Pick dead petunias. Keep the petunias in bloom throughout the season by picking dead flowers. Petunia multiflora does not require this treatment. Prune a third of the plant if it is too thin and not blooming well. This method will stimulate new growth and freshness of the plant.
Step 2. Apply the right amount of fertilizer
You need to make sure your petunia plants are healthy without applying too much fertilizer. If the petunia leaves look healthy and fresh, but the plant isn't blooming yet, or there aren't many flowers, you should reduce the amount of fertilizer you apply.
- The proper frequency of application of fertilizer is once a month, as this will ensure good growth without over-fertilizing.
- However, in petunias that have many petals, fertilizer should be applied every two weeks.
Step 3. Water well
Most petunias are not very dependent on water. So you can water it once a week, unless the weather in your garden is very dry. You will need to provide water to a depth of 14 to 20 cm each time you water your petunia.
- Creeping petunias need to be watered more often (more than once a week).
- Petunias grown in pots also need to be given more water depending on the size and volume of soil in them. Often times, potted petunias need to be watered once every day.
- The rule of thumb is to allow the top 2.5 cm of soil to dry before you re-water.
Part 4 of 4: Solving Petunia Growth Problems
Step 1. Control pests in your garden
You may notice aphids and caterpillars, both of which are pests that damage petunias. You must get rid of these animals so that your petunias can grow well.
- If you see aphids, be sure to repel them by spraying water on your plants. Do this until the aphids go away.
- Watch out for black spots and small holes on the leaves and flower buds that could indicate that caterpillars have invaded your petunia. Solve this problem with environmentally friendly insecticides.
Step 2. Water evenly
Sometimes, new flowers will shrivel before blooming. This is because you are not watering the petunias evenly. Allow the top layer of soil to dry first, then water it evenly.
Be sure to water at the base of the plant and not the plant itself
Step 3. Avoid petunia plant diseases
There's not much you can do when plant diseases like soft rot and mildew strike. But if you live in an area with heavy rainfall, you may want to try growing rain-resistant multiflora, as opposed to other types of petunias.
