Yellowing leaves and spindly or weak growth of geranium plants indicate a health problem that can cause a lack of growth, weak or limited flower production or the death of the plant, depending on the cause. A variety of growing situations can lead to yellow leaves and spindly growth.
Some of the main causes of weak growth include a lack of sunlight, water or nutrients. Improper growing conditions and overcrowded planting can lead to spindly or straggling growth and yellowing leaves. Nutrient and moisture deficiencies weaken the geranium, turning leaves yellow. The placement of the geranium has a major effect on its health. Additional causes of weak growth and yellow leaves include diseases that affect geraniums, some of which are fatal to the flower.
Giving geraniums the right amount of sunlight is key to healthy growth and green leaves. Geraniums need full, direct sunlight during the day to grow and blossom correctly. If growing geraniums indoors, keep them in a south-facing window to provide them with enough light, or provide an artificial grow lamp. Fertilize geraniums in the spring with a fertilizer targeting flowers to give the geranium the right amounts of nitrogen, phosphorus, potassium, iron and other necessary nutrients.
Geranium plants placed too close together or producing too many stems and flowers are unable to sustain growth due to competition for water, nutrients and light. Thin out the area around the geraniums to free up root space and encourage healthy growth. Remove the weaker growths from a spindly plant to encourage the remaining portions of the plant to grow healthy green leaves and thicker stems. Reducing crowding keeps geraniums producing flowers and green leaves.
Root rot and a variety of bacterial wilts cause yellow leaves and wilting of geranium plants. These diseases are spread by air- or soil-borne pathogens and pest insects like aphids. They affect geraniums’ growth and can prevent flowering. If left untreated, these diseases can be fatal for geranium plants. Treat affected plants with cultural controls like replacing planter soil and pruning affected leaves. Treat the plant with a fungicide or bacterial treatment to fight off the disease.