If the petunias on your windows suddenly turn yellow and are no longer very decorative, then they have chlorosis.

In the case of iron deficiency, only the leaf veins initially remain green

Like all our plants, our balcony flowers also need the right nutrients to grow magnificently. If your petunias (Petunia) are turning yellow in leaves, especially young leaves, then the most likely cause is chlorosis caused by a nutrient deficiency.

Detecting chlorosis in petunias

The missing nutrient is iron (Fe-ferrum). A typical symptom of chlorosis in petunias is the green leaves turning yellow, but the leaf veins remain green. Plants need iron for the formation of enzymes, for metabolism, for the formation of chlorophyll and thus also for respiration and photosynthesis. However, if this nutrient is missing, not only does the visible discoloration occur, but the lack of chlorophyll also impedes photosynthesis and the plants can no longer produce certain enzymes and hormones.

How to recognize an iron deficiency in your petunia or surfinia:

  • Young leaves are affected
  • The leaves turn yellow, only the leaf veins remain green
  • Growth disorders

Preventing chlorosis in petunias

To avoid problems with chlorostic petunias due to iron deficiency in the first place, here are a few tips for you. Since petunias are so-called heavy feeders, they need a lot of nutrients and also a lot of water.

However, you should also pay attention to the irrigation water. If you always water the petunias with hard water from the tap, i.e. water that contains a lot of lime, the pH value in the soil can change. A changed pH value can mean that certain nutrients - such as iron if the pH value in the soil is too high - can no longer be absorbed or can only be absorbed to a significantly lesser extent. You should therefore use soft water (rainwater) for watering if your water from the tap is very calcareous.

No hard water should be used for watering

Use a loose and nutritious substrate when planting to give your petunias a good start in life. Repotting in fresh soil can also be helpful, especially for potted petunias that are showing symptoms of chlorosis. This gives the plant fresh nutrients again, because the many watering can wash out many nutrients that the plant needs. Repotting after the winter is also beneficial and recommended. Learn more about overwintering and proper care for petunias here.

Potting potted petunias can also help with fresh soil

Calc and pH: what else you should know about it

There is always a lot of talk about pH and limescale, so what's it all about? The pH value expresses the concentration of hydrogen ions, so the more hydrogen ions there are, the more acidic the solution is.

The terms acidic, basic, alkaline and neutral are used again and again in connection with the pH value:

  • Basic and alkaline mean the same thing, namely a pH above 7.5
  • neutral means a pH value of 6-7.5
  • Acidic means a pH below 6
You can read the pH value on a pH scale

For the plants, the pH value of the soil is important for the availability of nutrients, also known as nutrient s alts. The optimal pH for most plants is between 5.5 and 6.5. Extreme pH values can damage plant organs. Extremely high or low pH values are also responsible for the fact that nutrients are fixed in the soil and are not available to the plants.

An increased pH value causes a lack of phosphorus or iron, whereas a low value results in a lack of magnesium or molybdenum, for example. This nutrient deficiency is caused by the unavailability of these nutrients and is caused by pH.

The water hardness is determined by calcium and magnesium carbonates and has an alkaline effect. As a result, the pH of the substrate can be influenced by watering. Hard water can increase pH. You can recognize hard water by the white crusts forming on all objects that come into contact with the tap water, such as in the kettle, on the taps or in the shower cubicle.

Control and Treatment of Chlorosis in Petunias

The chlorosis in petunias is light againto get rid of. The easiest way is through correct and adjusted fertilization.

Fertilize petunias

Treat your petunias with a special surfinia and petunia fertilizer. In addition to the nutrients nitrogen (N), phosphorus (P) and potassium (K) that are needed in the greatest amount, these NPK fertilizers also contain iron (Fe) and support your flowers in growth. You can use petunia fertilizer regularly, depending on the fertilizers used. This can also prevent deficiency symptoms.

Special petunia fertilizers can prevent deficiency symptoms

These fertilizers are available in liquid form and are simply added to the irrigation water. But there are also fertilizers in solid crystalline form that are simply dissolved in water. Since iron can be absorbed by the petunias via the roots and leaves, foliar fertilization can also be used to counteract the iron deficiency.

Foliar fertilization for petunias

You can also use special iron-rich fertilizers with your petunias. These fertilizers also contain nitrogen to support growth. When spraying the leaves with iron fertilizer, you should avoid direct sunlight. Therefore, an application in the evening is recommended. Foliar fertilization is an optimal way to combat iron deficiency, as this fertilizer cannot be washed away with the irrigation water. Be careful with the dosage though: overdosing can do even more damage to your petunias.

Also avoid contact with the fertilizer solution as these iron fertilizers can leave unsightly rust stains on your clothes or on your floor.

Foliar fertilization is ideal because the fertilizer is not washed out with the irrigation water

Always pay attention to the recommended quantities, because oversupply can also damage your plants.

Peunia Rock Powder

You can also put rock flour into the soil to compensate for the iron deficiency. Rock flour can also be brought in when planting to provide the petunias with nutrients right from the start.

Here you can find out more about the right care for petunias and how best to get them through the winter.

We recommend these products to treat & prevent chlorosis:

  • pH soil test set: Soil test set for easy and precise determination of lime requirements. Set is enough for 8 applications.
  • Floragard Bio Rhodohum: Organic special soil without peat for planting lime-sensitivebog plants. The organic fertilizers Flora-Bio-Mix and Flora-Phyto-Mix ensure he althy plant growth and magnificent flowers, and the low pH value optimizes the nutrient supply for he althy growth.
  • Floragard Compost Soil: Special soil made from weed-free compost and selected peat qualities. It supplies your plants with all the important nutrients over a long period of time and evenly, and the high humus content makes light and heavy soil fertile.
Floragard Rhodohum 40 L • Special soil • for raw ododendrons, azaleas,… €10.99Details →Floragard compost soil 60 L€9.99Details →

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Garden Design