Yellow leaves can indicate a nutrient deficiency in geraniums. We explain how to correctly identify and combat chlorosis in geraniums.

Chlorosis is a yellowish discoloration of the geranium leaves

Many people decorate their windowsills and gardens with geraniums, also known as pelargoniums (Pelargonium). They bloom in a wide variety of colors - from white to pink to various shades of red. Here's what you can do to prevent unsightly yellow discoloration on geranium leaves.

There are many different causes of chlorosis in geraniums - from a lack of nutrients to temperature fluctuations.

Detecting chlorosis in geraniums

Different types of chlorosis can appear on geraniums. For example, chlorotic yellow spots form all over the leaves, or chlorosis begins at the edge of the leaf or at another part of the leaf. What all chlorosis have in common is the yellowing of the green leaves, which can lead to the death of the leaf tissue, a so-called necrosis.

Reasons for chlorosis on geraniums

One of the most common causes of geranium chlorosis is a nutrient deficiency. Depending on the type of deficiency, the chlorosis occurs in different places. Therefore, observe the geranium leaves closely to determine what nutrient deficiency it could be:

  • Boron Deficiency: Necrotic and chlorostic spots form at leaf base on middle-aged leaves and spread along veins
  • Iron deficiency: yellowing of the young leaves between the leaf veins
  • Copper deficiency: yellowing starts at the base of the leaf and spreads to the edges of the leaf
  • Magnesium deficiency: yellowing of the older leaves between the leaf veins
  • Phosphorus deficiency: chlorotic spots on lower, older leaves that expand and turn reddish-purple
Check the leaves of your geranium to determine what nutrient deficiency it has

However, there are also abiotic causes that can affect geraniums and trigger chlorosis.These include the following causes:

  • Sunburn: Indoor geraniums are often burned through the glass by the sun and then show yellow-brown spots; sunburn also causes necrosis (dead brown leaf zones)
  • Heat damage: At temperatures above 28 °C, chlorosis and later necrosis can occur on the shoot tips
  • Cold damage: At temperatures below 8 °C, chlorosis forms on the tips of the shoots
  • Temperature fluctuations: Cold nights combined with warm daytime temperatures can cause yellowing of older leaves; red leaf edges can also occur

The growth conditions are also decisive for the occurrence of chlorosis on geraniums. Pests such as whitefly (Trialeurodes vaporariorum), spider mites (Tetranychidae) or mealybugs (Pseudococcidae) can also cause yellow discoloration, but this is only damage caused by sucking insects.

Prevent chlorosis on geraniums

As mentioned above, chlorosis can have many different causes, so there are many methods of preventing chlorosis.

First and foremost, this includes an optimal supply of nutrients. With appropriate fertilization, chlorosis can be prevented from the outset. Also, make sure your geraniums don't thrive in a pot that's too tight, as this can not only result in nutrient deficiencies, but also deplete the soil and limit the absorbency of the roots. Provide the geraniums with plenty of nutrients right from the start by mixing a fertilizer with the substrate when planting. Special flower fertilizers are suitable for this, such as the Plantura organic flower fertilizer, which contains 4% nitrogen, 2% phosphorus and 7% potassium and thus guarantees your geraniums a good supply of nutrients. Here you can find out more about the ingredients and the application of the Plantura organic flower fertilizer. You can find information on caring for geraniums in our special article.

Fertilize your geraniums with an organic slow-release fertilizer from the start to prevent chlorosis

Since chlorosis can also be caused by external factors such as temperature, you should avoid exposing your geraniums to temperatures below 8°C or above 28°C. Indoor geraniums often suffer from sun damage - especially the leaves that are attached to the window panes. Such locations should therefore be avoided.

You can with yellow boardsmonitor whether the discoloration is caused by pests such as whitefly or has another reason. You can simply put them in the flower boxes and check regularly whether animals are sticking to the layer of glue. You can find out more about yellow boards and which pests they can be used against here.

Remedy chlorosis in geraniums

If your geraniums suffer from chlorosis caused by a lack of nutrients, you can easily remedy this by fertilizing. You can use special geranium fertilizers that not only contain nitrogen, phosphorus and potassium, but usually also have an extra shot of trace nutrients. These fertilizers often come in liquid form, so you can simply mix them with the irrigation water and fertilize the geraniums with it.

If your geraniums are planted in a pot that is too narrow, there is no avoiding repotting. The additional space and the fresh and nutrient-rich substrate will help the geranium get going again. You can also mix fertilizer with the plant substrate when repotting to give your geraniums the best possible care. Here's everything you need to know about planting geraniums.

If your geraniums are planted in a pot that is too narrow, you should repot them

Preventing Geranium Chlorosis Summary:

  • Balanced nutrient supply
  • Use flower or geranium fertilizer
  • Do not place in pots or flower boxes that are too narrow
  • Avoid temperatures below 8 °C and above 28 °C

You can find more information about caring for geraniums here in our special article.

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Garden Design