Geraniums are popular flowering plants, often chosen for their vibrant blooms and attractive foliage. Yellowing leaves on a geranium are a common concern, indicating an underlying issue rather than a disease itself. Understanding the causes of this yellowing is the first step toward restoring plant health.
Environmental and Care-Related Causes
Yellowing leaves on geraniums frequently stem from imbalances in their growing environment or improper care practices.
Watering Imbalances
Overwatering is a common cause of yellowing. Consistently wet soil can suffocate roots and lead to root rot, causing leaves to turn yellow and appear droopy, particularly the lower leaves. Conversely, underwatering can also cause yellowing, though it is less common for these drought-tolerant plants. Under-watered geraniums typically show yellowing at the leaf edges and tips, which may also become dry and crispy.
Nutrient Deficiencies
A lack of essential nutrients can cause geranium leaves to yellow. Nitrogen deficiency commonly results in overall yellowing of older, lower leaves, often stunting the plant. Iron deficiency often manifests as interveinal chlorosis, where areas between leaf veins turn yellow while veins remain green, typically affecting younger leaves first. Magnesium deficiency also presents as interveinal chlorosis, but it generally appears on older, lower leaves.
Insufficient Light
Geraniums require adequate sunlight for photosynthesis and healthy foliage. If a geranium does not receive enough light, its leaves may turn pale green or yellow due to reduced chlorophyll production. This issue is especially noticeable on older leaves or those in shaded parts of the plant. Geraniums generally thrive with at least six to eight hours of direct sunlight daily.
Temperature Extremes
Both excessively hot and cold temperatures can stress geraniums, leading to leaf yellowing. Sudden cold snaps, especially in spring or fall, can cause leaves to discolor. Prolonged exposure to high temperatures or harsh, direct sun can also induce stress and yellowing. Geraniums typically prefer daytime temperatures between 65 and 70°F and nighttime temperatures above 55°F.
Pests and Diseases
Pests and diseases can contribute to yellowing leaves on geraniums. Their presence often comes with other distinct symptoms that aid in identification.
Common Pests
Common garden pests feed on geranium leaves, causing them to yellow. Spider mites, for instance, pierce plant cells and suck out sap, resulting in tiny yellow stipples on the leaves, which can eventually lead to widespread yellowing. Aphids and whiteflies are other sap-sucking insects that can cause leaves to yellow and wilt due to nutrient depletion. A sticky residue, known as honeydew, may also be present on affected leaves.
Fungal and Bacterial Diseases
Several diseases can cause yellowing or yellow spots on geranium leaves. Geranium rust, caused by the fungus Puccinia pelargonii-zonalis, typically begins as small, pale yellow circles on the underside of leaves. These spots develop into rust-colored pustules, with corresponding yellow spots on the upper leaf surface, leading to yellowing and leaf drop. Bacterial blight, caused by Xanthomonas campestris pv. pelargonii, can manifest as small yellow spots that enlarge and become necrotic, often with V-shaped yellow areas or general yellowing, and may be accompanied by wilting.
Other Contributing Factors
Beyond environmental stressors and biological threats, some natural processes can also lead to yellowing in geranium leaves. These factors are generally not indicative of a severe problem.
Natural Leaf Senescence
As geraniums mature, it is natural for older, lower leaves to yellow and eventually drop. This process, known as senescence, allows the plant to reallocate energy and nutrients to new growth. Yellowing on only a few of the oldest leaves, particularly those at the base of the plant, is typically not a cause for concern.
Transplant Shock
The stress of repotting or transplanting can temporarily cause geranium leaves to yellow. When a plant is moved, its root system can be disturbed, and it needs time to adjust to new soil, temperature, and moisture conditions. This temporary yellowing is a plant’s response to the change in environment and typically resolves as the plant establishes itself in its new location.
Reviving Your Geranium and Preventing Future Yellowing
Addressing yellowing leaves involves identifying the specific cause and adjusting care. Proper watering is a primary step. Geraniums prefer their soil to dry out between waterings; checking soil moisture about an inch below the surface helps prevent over and under-watering. Adequate drainage in pots is also important to avoid waterlogging.
Balanced nutrition through regular fertilization corrects nutrient deficiencies. A balanced, slow-release fertilizer applied at the beginning of the growing season helps supply essential nutrients like nitrogen, iron, and magnesium. Geraniums thrive with ample sunlight, typically requiring at least six hours of direct sun daily. If light is insufficient, relocating the plant or pruning nearby foliage to increase light exposure can be beneficial.
Maintaining stable temperatures is important, as geraniums are sensitive to extreme heat or cold. Protecting them from sudden temperature drops or intense, prolonged heat can minimize stress. Regularly inspecting plants for signs of pests or diseases allows for early intervention, though specific treatments vary depending on the issue. Ensuring good air circulation around plants can also deter fungal problems.