Petunias, scientific name Petunia atkinsiana, comprise 20 species of flowering plant. They have exceptional blooms with a long flowering period. These plants are considered annuals, but in some areas they are perennials and bloom from spring until close to wintertime. They are usually placed in hanging baskets, containers, and as seasonal groundcovers. As with most plants, petunias may suffer disorders that cause yellowing leaves.
Petunia leaves turning yellow: Common reasons
Iron deficiency
Chlorosis may occur in young petunia plants if they have an iron deficiency. This abnormal reduction or loss of normal green color leads to yellowing leaves, while the leaf veins remain green.
Plants need iron for chlorophyll production, which is vital for photosynthesis. If iron is deficient, photosynthesis is impeded and plants cannot synthesize enzymes and hormones.
Signs of iron deficiency may include the following:
- The young leaves are affected.
- The leaves become yellow, although the veins are still green.
- The plants’ growth is disturbed or becomes stunted.
Using hard water from the tap when watering your petunias could change the soil pH due to the presence of lime. Changes in pH levels could mean that nutrients such as iron can no longer be absorbed. Use soft water or rainwater for watering if your tap water contains too much lime. Repotting your plants using fresh soil is also helpful.
To correct iron deficiency, you need to acidify the soil. Apply iron fertilizer to the soil to enrich it, or spray some on the plants’ foliage.
Diseases
Yellowing petunia leaves could be due to a disease caused by the tobacco mosaic virus. This is usually transmitted by aphids or through the soil, and is manifested by golden yellow mottling.
To fix the problem, you need to dispose of the infected plants. There is no cure for this viral infection. Do not add the discarded plants to the compost pile, as the disease could then spread to other parts of your garden.
Fungal diseases could also invade your petunia plants. These include crown, stem and root rot, as well as Verticillium wilt. These fungal infections are hard to control. You need to remove and destroy the infected plants to prevent any spread to healthy plants. Prune out the damaged plant parts and dispose of them in a covered container or burn them.
Since humid conditions can exacerbate the problem, make sure that you water plants deeply to a depth of around six inches and allow the top one inch of soil to dry out before watering again. Water only at the base to keep the foliage dry, and provide plenty of air circulation.
Overwatering
Petunia leaves tend to turn yellow if the plant gets too much water. These plants like plenty of water, but do not like their leaves and petals to remain wet. If the plants are overwatered they tend to turn yellow and become wilted.
To correct the problem, water from the base of the plant and let the top few inches of soil dry out before watering again. See to it that the soil is a well-draining mix; ideally it should be half peat moss and half soil. The purpose of peat moss is to provide the right amount of acidity to the plants.
Pests
Aphids commonly attack petunia plants and if the infestation is severe they could cause leaves to become yellow and stunted. In case of a light infestation, you can dislodge the pests by spraying them with a strong stream of water. However, for severe infestations, you need to spray the plants with insecticidal soap every four to seven days until all the pests have been exterminated.
For best results use a commercial spray, or you can add two to five tablespoons of regular liquid dish soap to a gallon of water. Spray on both sides of the leaves, but do not apply insecticidal soap when the temperature is above 90 degrees Fahrenheit as the leaves may be scorched.
Petunia care
Petunia plants are fairly heat-tolerant so they do not have to be watered too frequently. A weekly, thorough watering should be sufficient unless there is a drought in your area. Do not water shallowly as it may encourage shallow roots. Petunias in containers and the spreading types may require more frequent watering compared with those planted in the ground.
Ideally, these plants should be fertilized monthly with a balanced fertilizer to aid heavy blooming and rapid growth. Bi-weekly doses of fertilizer may be given to double-flowered cultivars.
Conclusion
Petunias are popular annual plants with bountiful flowers. However, they are also prone to certain conditions that cause yellowing leaves, which may include iron deficiency or pest infestation. It may also be brought about by fungal or viral diseases, such as the tobacco mosaic virus.
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