7 Reasons The Leaves on Your Petunias are Turning Yellow

You arrive in mid-summer, and your petunias have been growing so well and have put out multiple blooms already.  But you notice the leaves are starting to turn yellow. There could be many reasons the leaves of your beloved petunias are turning yellow, and I’m here to help you find the root cause of why your leaves are yellowing before it’s too late.

Petunias are a cult classic for good reasons. They come in many colors and sizes, and each variety will provide a flood of color from spring to fall. They can be grown in zones 2-11, a large range for such a delicate flower. They are considered perennial, but in northern regions of the United States, they are usually grown as an annual.

Figuring out the issue and fixing it early will ensure your petunia plants continue to bloom well for the remainder of the season. Let’s discuss why your petunia leaves are beginning to yellow and ways to fix them.

Improper Sunlight

Petunias love the sunlight and can’t get enough of it. If you want thriving petunias, plant them in an area that receives at least 6 hours of sunlight per day. More light is generally better for petunias, so 8 hours or more of sunlight is ideal.

Plants grown in areas with less than 6 hours of sunlight per day may begin to wilt, brown, or die. Shade is the number one killer of petunias. However, they can handle dappled shade or even a few hours of shade in the hotter late afternoon hours. Before you plant your flowers, choose a location that receives enough sunlight.

Remember that as the season changes, so will the angle of the sunlight in your yard. A location once in the full sun could become partially to fully shaded. The sun begins to shift, and a tree or building could obstruct the light. This could explain why you have yellowing leaves on your petunias later in the season.

Overwatering

When petunias are overwatered, their leaves will begin to turn yellow. Petunias are not big fans of soggy soils and grow best in well-draining soils. Overwatering is more common in flower beds, landscapes, and vegetable gardens. These soils may have a difficult time draining water.

Soils with high clay content have the most difficulty draining. Incorporating organic matter is a great way to improve drainage. This should be done before you plant. If you try to incorporate organic matter when plants are established, you risk damaging the roots during incorporation.

Hanging baskets and containers typically don’t have issues with overwatering, but soils should be monitored to prevent overwatering. Stick to watering potted flowers 2 to 3 times per week. No matter where you have your petunias planted, regularly check the soil moisture.

Underwatering

As with overwatering, leaves may turn yellow if they don’t receive enough water. Petunias benefit from a good soaking once or twice a week. Soaking the area encourages deeper root growth and helps create a drought-tolerant plant.

If roots are shallow, they tend to struggle with dry soil and can die quickly. Thoroughly watering the area should help this problem. Soaking also allows water to travel deep into the soil that petunias can tap into during dry periods.

Hanging baskets tend to dry out quicker than those planted in the ground. Containers should be watered two or three times a week to prevent drought-like conditions.

Allow water to flow freely from the bottom of the basket or container. This indicates that water is moving through the entire basket or container. The soil in the hanging basket or container should be moist to throw the whole container when finished watering.

Nutrient Deficiency

Petunias are hungry plants and will quickly deplete the nutrients from the soil around them. Adding fertilizer to your soil will help prevent them from turning yellow from lack of nutrients. Fertilizer should be applied the day you plant your flowers in your desired location.

Slow-release fertilizers are a great option because they release the proper nutrients over time. Slow-release organic fertilizers must break down to release nutrients in the soil and, as a result, don’t leach from the soil as chemical varieties do.

Liquid fertilizers can also be used but tend to have more leaching issues as the nutrients are not held in organic material. As a result, water might carry a liquid fertilizer away before the plants can utilize it. Also, conventional (non-organic) liquid fertilizers may burn delicate leaves. This doesn’t mean you can’t use them, but be aware that synthetic fertilizers tend to be much more potent and that their potency can cause damage to tender young plants.

Don’t forget about your hanging baskets and pots! They will also need fertilizer, possibly even more often, due to a more frequent watering schedule. Water will carry away nutrients quicker from containers. Consider applying fertilizer weekly to monthly with these types of containers.

Diseases

Right next to pests, diseases are one of gardeners’ worst nightmares. Petunias generally are disease-free, but occasionally they become infected. A common disease that turns leaves yellow is tobacco mosaic virus.

Tobacco mosaic virus will cause mottling of the leaves in a golden yellow pattern. This disease is transmitted by aphids, thrips, leafhoppers, and other piercing-type pests and can affect several other plants like cucumbers, tomatoes, and peppers, to name a few. This virus has no cure, and diseased plants should be discarded. Do not compost infected plant material.

Crown and root rot is another disease that manifests as yellowing leaves. This disease affects the root area and is difficult to catch. You won’t notice the disease until the plant begins to die. This is common in poorly drained soils, and the drainage of those soils should be improved. Carefully remove plants, improve the soil, and replant. While out of the soil, examine the roots for any signs of rot and cut off the rotten material, carefully avoiding injuring healthy roots.

Pests

Pests will literally suck the life out of plants and cause many problems. The number one pest that will cause yellowing leaves is aphids, the most common and dreaded pest for gardeners. They love to suck the sweet sap from the leaves of these plants.

Aphids are treatable if caught soon enough. They will appear on the new, fresh growth of plants. They live on the underside of leaves, so you may not notice them immediately. Not only do they slowly kill the leaves, but aphids can also transmit diseases from one plant to another.

To remove aphids, start with a water treatment; most aphids can’t climb back up onto the plant if blasted off with a strong spray of water. If the aphids are present in large numbers, consider removing heavily-infested leaves if the plant can handle the pruning.

An insecticide may be necessary if the plant is very young or has few healthy, uninfested leaves. Organic options include neem oil or pyrethrin, but be careful to follow all label directions and try to spray when pollinators are not present.

Early Frost

Petunias are tender perennials or annuals, depending on your climate. They are sensitive to colder temperatures; leaves will begin to turn yellow and shortly after die if they are nipped by frost. If your region is expecting its first frost, there are a few ways to protect them and make them last a bit longer.

If you have planted petunias in containers or hanging baskets, you can bring them inside. Bring them into an insulated garage or into the house. This will extend the life of your flowers by many weeks. If your petunias are planted into the ground, you can cover them with old towels and sheets to protect them from frost.