Why Are My Nasturtium Leaves Turning Yellow?

Nasturtiums are a favorite in many gardens, admired for their vibrant, edible flowers and distinctive, round leaves. While considered low-maintenance, these plants can still present challenges. One of the most frequent concerns for gardeners is the appearance of yellow leaves, which can detract from the plant’s beauty and signal an underlying issue. Understanding the reasons for this color change is the first step toward restoring your plant to health.

Primary Causes of Yellow Nasturtium Leaves

Watering Issues

Improper watering is a frequent reason for yellowing nasturtium leaves. Overwatering is a common mistake, leading to soil that is constantly saturated. This condition deprives the roots of oxygen, causing them to rot and preventing them from absorbing nutrients, which results in leaves turning a limp, sickly yellow. To check for this, insert your finger about an inch into the soil; if it feels soggy, you are likely watering too much.

Conversely, underwatering can also cause leaves to yellow. When the soil becomes too dry, the plant conserves water, causing the leaves to turn yellow and often become dry and crispy to the touch. Nasturtiums prefer consistently moist but not waterlogged soil. A good practice is to water deeply when the top inch or two of soil feels dry.

Nutrient Imbalance

A surprising cause of yellow leaves in nasturtiums is an excess of nutrients. These plants thrive in poor, less fertile soil and do not require supplemental feeding. Adding fertilizer, particularly one high in nitrogen, can be counterproductive. Too much nitrogen encourages the plant to produce abundant, lush foliage at the expense of flowers and can also cause the leaves to develop a yellow hue. If you have been fertilizing your nasturtiums, the solution is to cease feeding them immediately.

Pest Infestations

Pest infestations can lead to a decline in plant health, often manifesting as yellow leaves. Aphids are common pests for nasturtiums, drawn to the plant’s tender new growth. These small, sap-sucking insects drain nutrients from the leaves, causing them to develop yellow spots or stippling, curl, and eventually die. Inspect the undersides of leaves and the stems for clusters of these tiny insects. A strong spray of water from a hose can often dislodge them, and for persistent infestations, applying a horticultural soap is an effective control method.

Environmental Stress

Environmental factors can also contribute to yellowing leaves. While nasturtiums enjoy sun, too much intense, direct sunlight can cause sunscald. This appears as bleached or yellowed patches on the leaves that are most exposed to the sun. Transplant shock is another form of stress that can cause temporary yellowing as the plant adjusts to its new environment.

Natural Aging

Not all yellow leaves are a sign of trouble. It is a normal part of the plant’s life cycle for the oldest leaves, typically those at the base of the plant, to gradually turn yellow and fall off. As the plant grows, it directs its energy toward producing new leaves and flowers. If the yellowing is confined to a few lower leaves and the rest of the plant appears healthy and vigorous, there is no cause for concern.

Managing Plants with Yellow Leaves

Once you have identified the cause of the yellowing, it is beneficial to remove the affected foliage. This practice, known as pinching, improves the plant’s appearance and redirects its energy toward healthy growth and flower production. Use clean scissors or pruning shears, or simply pinch the leaf stem off near the main stalk. Removing the damaged leaves also improves air circulation around the plant, which can help prevent fungal diseases.

If the yellowing is widespread and the plant shows little sign of new growth, it may be too stressed to recover. However, if the majority of the plant remains green and vibrant, it will bounce back quickly once the underlying issue is resolved.

Preventive Care for Healthy Nasturtiums

To prevent yellow leaves, focus on providing the right growing conditions from the start. Plant your nasturtiums in a location that receives at least six hours of sunlight per day, with some protection from intense afternoon sun in hotter regions. Choose a planting site with well-draining soil to avoid root rot. These plants perform best in soil that is not overly rich, so refrain from amending it with compost or fertilizer.

Proper watering is key to keeping nasturtiums healthy. Water the plants when the top layer of soil becomes dry, providing enough to moisten the root zone thoroughly without becoming waterlogged. Simulating their preferred environment of lean soil and proper moisture levels helps avoid many common stressors.