The appearance of red or reddish-purple leaves on a geranium can be a sudden and concerning change for many gardeners. This visible shift in foliage color is a sign that the plant is experiencing some form of environmental or nutritional stress. While the symptom may appear alarming, the cause is often straightforward and easily corrected. This guide will help distinguish normal color changes from genuine problems and determine the correct course of action.
When Red Leaves Are Normal
Not every instance of red pigmentation signals a problem that requires intervention. Some geranium cultivars, particularly zonal geraniums, naturally possess a distinct ring or band of reddish-brown coloration on their leaves as part of their genetic makeup. This characteristic is a normal trait of the variety and does not indicate any distress.
For perennial geranium species, the leaves often develop intense red, burgundy, and orange hues in the autumn as a natural part of their seasonal decline. This process is similar to the fall foliage change seen in trees and is a response to cooling temperatures and reduced daylight. Furthermore, minor, transient reddening can occur during brief environmental transitions, such as moving a plant outdoors in the spring, which typically resolves itself as the plant acclimates.
Diagnosing the Primary Causes of Red Leaves
The most frequent cause of widespread red foliage is temperature stress, specifically exposure to cold. Geraniums are sensitive to temperatures below approximately 50°F (10°C), which disrupts the plant’s ability to efficiently transport nutrients. This stress triggers the production of anthocyanin, a red-to-purple pigment that accumulates in the leaves, masking the green chlorophyll. The reddening typically begins at the leaf margins and progresses inward, often affecting the entire plant uniformly.
A second common culprit is phosphorus deficiency, which is often linked to cold temperatures. Phosphorus is a relatively immobile nutrient, and its uptake is severely limited in cool or poorly draining soil. The symptoms of deficiency manifest as a darker, purplish-red discoloration, primarily on the older, lower leaves of the plant, frequently accompanied by stunted growth. This occurs because phosphorus is essential for energy transfer.
The pattern of discoloration helps differentiate these two primary causes. Cold stress typically causes a brighter, more uniform red or magenta color on both new and old foliage, especially after a cold night. Phosphorus deficiency results in a deeper, purplish-red hue concentrated on the oldest leaves at the base of the plant. A third, less common cause is fungal disease, such as geranium leaf rust, which presents as small, reddish-brown lesions or rings, most prominently on the underside of the foliage, often with powdery spores.
The Action Plan for Treatment and Removal
The question of whether to remove red geranium leaves depends entirely on the cause and the leaf’s condition. For leaves reddened by cold stress or nutrient deficiency, removal is generally unnecessary unless the foliage is completely withered or necrotic. Even discolored leaves contribute some energy to the plant and should be left in place until the plant has recovered and produced new, healthy green growth.
If the diagnosis points to cold stress, move the geranium to a warmer location where the temperature remains above 55°F (13°C). For plants outdoors in the spring, this may mean providing temporary cover during cold nights. Restoring the plant to its preferred temperature range allows nutrient uptake to normalize, and new leaves will emerge without the red pigmentation.
In cases of confirmed phosphorus deficiency, apply a balanced, water-soluble fertilizer with a slightly higher phosphorus ratio to the soil. Since cold weather often causes this deficiency, ensuring the root zone is warmer will also aid in the uptake of the applied nutrient. For fungal issues like leaf rust, physically remove and destroy all affected leaves immediately to prevent the spread of spores. Ensure the plant has good air circulation, and avoid overhead watering to keep the foliage dry.
When removing any leaves, use clean, sharp shears to make a precise cut at the base of the leaf stem. Sterilize your cutting tool between plants to avoid accidentally transmitting any pathogens. Focusing on correcting the underlying cause—temperature, nutrition, or disease—is the most effective way to restore the geranium’s vibrant green foliage.