When the leaves of petunias turn yellow, the so-called chlorosis is most often responsible. With the right measures, however, the problem can be prevented and the plant saved.

In a nutshell

  • Chlorosis is one of the most common causes of yellow petunia leaves
  • Prevention is possible through good care
  • other deficiencies can also be responsible
  • Plants can usually be saved with timely intervention

Possible causes

If petunia leaves are turning yellow or fading, one of the most common possibilities is something called chlorosis. However, other factors may also be responsible. These include:

  • wrong location
  • insufficient incidence of light
  • improper care
  • Hibernation error

Before the right measures can be taken to save the plant and prevent further damage, the culture conditions should therefore be checked and adjusted if necessary.

chlorosis

Chlorosis is an iron deficiency in the plant. This can also be present if it is fertilized regularly. A too high lime content in the substrate or in the irrigation water is then responsible. With the resulting pH value, the petunia can only absorb certain nutrients in insufficient quantities or not at all.
However, iron in particular is needed to form certain enzymes and hormones. These, in turn, are crucial for the petunia's respiration and the process of photosynthesis to generate energy. Chlorosis can be recognized by the following signs:

  • yellow leaves but green veins
  • especially young leaves affected
  • growth disorders

In order to prevent it or treat the affected plant appropriately, several factors must be taken into account.

Example of leaves discolored by chlorosis; Source: Dacnoh, Capsicum annuum clorosis, edited by Plantopedia, CC BY-SA 3.0

PH value

It is important to measure the pH of the substrate so that you can change the soil if necessary. Values between 5.5 and 6.5 are ideal for the petunia. This is the neutral to slightly acidic range.
If the soil is too acidic or too basic due to too much lime or other influences, the uptake of nutrients is disturbed. In this case, the substrate must be changed and both the fertilization behavior and the watering adjusted.

Tip: Corresponding tests can either be carried out with test strips from the pharmacy or the specialist trade, or a sample of the substrate can be submitted to the specialist trade for checking.

substrate

Optimal substrate for petunias is:

  • relaxed
  • fresh
  • rich in humus
  • nutritious
  • neutral to slightly acidic
  • does not tend to compress
  • has a low lime content

Since the petunia is a heavy feeder, it requires large amounts of nutrients. These, in turn, can only be absorbed from the earth if the substrate is suitable. Compost or potting soil are suitable.

pour

In addition to the substrate, watering or the water used for it also plays a crucial role in caring for the petunia and preventing chlorosis or other deficiencies. If the water used is very hard - i.e. has a high lime content - the lime is gradually deposited in the substrate and on the roots. The roots can only absorb the nutrients from the soil to a reduced extent or not at all and the crop is undersupplied. This is often the case when tap water is used. Because especially in Germany this is very hard in many places.
The following sources are available as alternatives:

A regular water supply is imperative.
  • collected rainwater
  • Water from aquarium or pond
  • filtered tap water
  • stale tap water

Because petunias require a lot of water, stagnant tap water is often the most viable solution. This is especially true if it is cultivated on the balcony and there is no possibility of using rainwater or pond water. Before watering, tap water is left in a watering can or bucket for seven days. The lime collects at the bottom of the vessel. Therefore, when watering, only use about two-thirds of the water for the petunias. The rest can be used for plants that have a high lime tolerance.

Notice: Petunia leaves can also turn yellow from lack of water or waterlogging. You should therefore check the humidity of the substrate at least once a week.

repot

Due to the high nutrient requirement and frequent watering, the substrate is quickly used up. On the one hand, the nutrients are absorbed by the plant and, on the other hand, are washed out by the water. A regular change of soil can therefore prevent the petunia leaves from turning yellow. An ideal time is at the end of hibernation, when you bring the plant back outside. The new shoot increases the nutrient requirement and this is covered directly by the fresh soil.

deficiencies

Not only chlorosis and thus an iron deficiency, but also other deficiencies can be responsible for yellow petunia leaves. In order to keep the leaves and the plant healthy overall, an adequate supply of nutrients is therefore required. Suitable means are:

Guano fertilizer is made from excrement from seabirds such as penguins or cormorants; Source: excrement from seabirds such as penguins or cormorants
  • guano
  • flowering plant fertilizer
  • from June iron fertilizer
  • special petunia, geranium or surfinia fertilizer

Tip: About four weeks after repotting, fertilizing can be done at intervals of one week. Liquid fertilizer is particularly easy to dose and can be added directly to the irrigation water, making it very easy and practical to use.

frequently asked Questions

Why are petunias more often affected in pot culture?

If the petunia is cultivated in a bucket, it has less substrate than outdoors. The soil dries faster and nutrients are also only available to a limited extent. Diseases, pests and deficiencies are therefore more common if care is not adjusted accordingly. The calcification of the substrate also takes place in a shorter time when using hard water in smaller planters.

How Often Should Petunias Be Repotted?

An annual change of soil in the bucket culture is optimal. The old substrate should be completely rinsed off the roots to remove any deposits, germs or pests that may be present. A drainage layer is also important to avoid waterlogging.

What Fertilizer Can Avoid Yellow Leaves?

Guano or liquid flowering plant fertilizer are usually sufficient if they are administered weekly. If chlorosis is already beginning or is present, an iron fertilizer should be used in addition to changing the substrate, using low-lime water and removing dead leaves. This can also be administered preventively from June to September, since the petunia has a high need for the mineral.

Category:

Garden plants