Why do plant leaves turn red?

March 2, 2021

What happens when leaves turn red on plants and what causes this reddening? We have all noticed seasonal changes in leaf color, especially on ornamental plants and trees. During the year the leaves of the plants turn yellow, while in several cases, especially in the autumn season before they fall, they show a red color.

The red color in the leaves is due to a group of pigments called anthocyanins, which are also found in red, purple and blue flowers. Anthocyanins have the ability to protect plants in adverse environmental conditions, as they contain antioxidants.

In addition to leaves and flowers, anthocyanins are also found in red fruits such as tomatoes, red peppers, blueberries and strawberries.

The formation of anthocyanins and reddening of the leaves occurs in many plants in the autumn season, but it can also be caused by other causes. Sometimes they are related to the normal functioning of the plants, while in other cases they are a sign that there is a problem in the growth of the plants.

In today’s article, we will analyze the reasons why plant leaves turn red, so that we know when it is a normal plant process and when extra care is needed to keep them healthy and full of life.

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When is it normal for plant leaves to turn red?

First, there are several types of plants that instead of green leaves, have red leaves. The appearance of red leaves is also normal on young plant leaves and on deciduous plants that shed their leaves in the fall. The leaves of the plants may also turn red as a protection against excessive sun exposure or severe frost conditions.

1. Plants that have red leaves

Some plants have a high concentration of anthocyanins due to their genetic characteristics. The high concentration of anthocyanins helps them cope with cold conditions, as well as intense sunlight.

Characteristic examples of plants with red and purple leaves are the barberry, the well-known hardy ornamental shrub, as well as the prunus or ornamental plum, the ornamental tree that beautifies parks, squares and sidewalks.

Barberry, a hardy shrub with red leaves

2. Red color in young plant leaves

The new leaves of the plants are extremely sensitive and usually grow in stressful conditions, such as intense heat and humidity. This sensitivity is observed until the leaves have completed increasing in size to then form the protective wax layer on their surface.

A typical example is the young rose leaves which are initially red. Gradually, as they ripen, they turn green and chlorophyll is formed by the function of photosynthesis.

The reddening of young leaves and the formation of anthocyanins helps plants retain water in the leaf cells, reducing losses due to evaporation.

Also, a typical case is the photinia, the favorite ornamental shrub, whose leaves are red in spring, turn purple in summer and turn green in winter.

Photinia, an evergreen shrub with red leaves

3. Red color in autumn leaves

Anthocyanins form in the leaves of deciduous plants in the fall, before they fall, and help transport sugars and carbohydrates to their woody part during the winter season to be used again the following year.

A typical example of plants that turn red leaves is the vine plant, the climbing plant whose green leaves, during the autumn months, take on an impressive red color before falling to the ground.

Grapevine, ivy the five-leaved

4. Leaves that turn red due to strong sunlight

Exposure of the leaves to strong sunlight can cause a red color to appear. Often, the leaves of a plant in a sunny location are redder in color than the leaves of the same plant in a darker location.

Due to the intense sun rays, anthocyanins are produced in the leaves to protect against sunburn and to better retain water inside the leaves.

5. Leaves that turn red due to severe frost

In some evergreen plants and trees that usually have broad leaves, such as viburnum lucidum, a red coloration is observed in the leaves during the winter months.

And in these cases, we have the formation of anthocyanins in the leaves for protection from the intense sun during frost. At the same time, anthocyanins act as a natural antifreeze for plant cells, preventing ice from forming inside the leaves.

Frost-reddened leaves on viburnum lucidum.

When do plant leaves not turn red naturally ?

Sometimes the leaves of plants show a red color due to abnormal factors due to adverse conditions, nutrient deficiencies or attacks by various insects.

a) Red leaves due to lack of nutrients

The lack of nutrients and especially phosphorus can cause reddening of leaves, and especially in intensive vegetable crops that are carried out for many years in the same field.

In this case, phosphorus fertilizer can be added to the soil to address the specific deficiency, or the foliage of the plants can be sprayed with foliar fertilizers.

What phosphorus offers as a fertilizer to plants and crops

b) Red leaves due to salinity and excessive fertilization

A high concentration of salts, as well as excessive fertilization with some elements such as zinc, can create toxicity in plants and cause reddening of the leaves.

In these cases, a soil analysis or leaf analysis helps to confirm the cause of the reddening of the leaves.

c) Red leaves due to poor drainage

When the water is not removed from the root system of the plants and we have too much moisture, there is a lack of oxygen and reduced water absorption by the leaves.

This can cause reddening of the leaves, especially in heavy clay soils, as well as new leaves appearing smaller than normal.

To avoid this, we can add various natural materials to improve the soil. Some materials that improve drainage in soil are manure, compost, perlite, zeolite, attapulgite and pumice.

How we use perlite in gardening

d) Red leaves appearing due to disease attack

Some plants when affected by various fungal and bacteriological diseases, may show red spots on the leaves. Disease infestation shows red spots, mainly on the inside of the leaf and not on its edges.

To deal with it we can spray with organic preparations that we get from agricultural stores, such as copper and sulfur.

How we use sulfur in plants (+video)

And a secret about the reddening of plant leaves

Many times, when plant leaves are torn, blown by wind or otherwise, reddening is observed in those areas of the leaf due to the deposition of anthocyanins by the plant’s protective mechanisms.

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