Geraniums have approximately 422 species, and are found in temperate areas of the world such as the eastern Mediterranean. These plants have broad circular leaves, with flowers that come in white, pink, blue or purple. They prefer fast-draining soil and can be propagated in autumn or spring by cuttings, seeds or by division. However, just like other plants, they can encounter problems like yellowing and leaf discoloration.
Geranium Leaves Turning Yellow: What Are The Common Causes?
1. Overwatering
Geraniums are sun-loving plants and native to temperate regions, so watering them too often can be detrimental. You will notice leaves yellowing at the bottom of the plants when they absorb too much water.
Water the geraniums only when they need it. You can easily check this with a finger test: When the top inch of soil is dry to the touch, it is an indicator that you should water the plants.
2. Underwatering
Although it is uncommon for geraniums to die from underwatering, this could produce similar symptoms to those of overwatering. When these plants are affected by drought, the edges of the leaves turn yellow.
To ensure you are watering correctly, check that the top one inch of soil is dry; if so, water the plant. If you are unsure whether or not to water, leave it for a day or two and re-check the soil.
When leaves are left wet for a long period, this could also cause bacterial leaf spots.
3. Insufficient or Too Much Sunlight
Geraniums adore the sun and need about four to six hours of full sun daily. The morning sun is ideal for these plants since temperatures are warmer during the afternoon. They grow well in the outdoors where there is full sun in the morning and light shade in the afternoon.
4. Cold Snaps
Cold snaps are immediate and fleeting spells of cold weather. These can cause geranium leaves to turn yellow, especially during an extended period of wet and cool weather. Frost damage is possible especially during early springtime, so it is best to keep up to date with weather forecasts. This will allow you to prepare by insulating your geraniums and other outdoor plants.
5. Micronutrient Deficiency
Geraniums need nutrients to grow healthily, just like other plants. Some of the essential nutrients include magnesium, sulfur, zinc and iron. The plants should be fertilized at least monthly or bi-weekly during the growing season. The ideal ratio is 20-20-20 to ensure that the nutrients are well-absorbed.
Magnesium affects the chlorophyll molecule responsible for the green pigment of plants, so a geranium deficient in magnesium will have yellowing leaves. Epsom salt is a good source of magnesium for your plants.
To check whether your plants lack vital nutrients, test your soil with a soil test kit. It should give you a pH reading and an electrical conductivity reading – a measurement of soluble salts in the soil. The Michigan State University guidance states that pH readings for zonal geraniums should be 6 to 6.4, while for the regal and ivy geraniums it should be 5.5 to 6.
6. Geranium Diseases
Certain diseases are attributed as causes for yellowing geraniums. These include the following:
- Bacterial blight – This is observed on the underside of the leaves and looks like V-shaped lesions and yellowish or brownish water spots. It can cause stem rot and affect the entire plant. Isolate the affected plant and sterilize all tools used on the plant to prevent cross-infection.
- Bacterial leaf spot – This disease is similar to blight, although no wilting will occur; only yellow spots. The main cause is due to leaves that remain wet for a long period. To avoid this, always water geraniums from below and do not include the leaves.
- Southern bacterial wilt – The symptoms are the same as for blight, but this disease starts at the soil line and goes upward, causing discoloration. While blight causes discoloration on the lower part of the plant, it is the other way around with Southern bacterial blight, since the progress is upward from the soil line.
- Viral infections – At least 15 viruses are known to affect geraniums, and it takes as long as three weeks before symptoms start to show. The virus will also likely spread to nearby plants because of water splashing or through insects like aphids. Viruses can also spread through the propagation of infected cuttings.
7. Herbicide Injuries
Weeding around geraniums could lead to accidents, especially when using herbicides. They could cause a bleaching effect on geraniums which could lead to yellowing leaves. A safe alternative to herbicides is to use mulch.
Conclusion
Geranium leaves turning yellow is not a pretty sight and could indicate a serious infection or disease. The common causes for this discoloration include overwatering, underwatering and exposure to too much sunlight. However, it could also be due to cold snaps, micronutrient deficiency or geranium diseases.
Image: istockphoto.com / Jonas Rönnbro