Broccoli Leaves Turning Purple: Causes, How to Fix and Prevent

Broccoli is a dark green plant in the cabbage family. The leaves, stalk, and flowering heads are edible vegetables. Broccoli plants are grown in many gardens worldwide.

Broccoli is relatively easy to grow as a potted home plant. A rich green broccoli plant turning purple usually catches gardeners off guard. You begin to wonder why the color of the plant suddenly changes. It is completely healthy to eat purple broccoli leaves. Nevertheless, find the causes of the purple leaves and fix the problem.

 a piece of broccoli on wooden board

How can the green color be restored and what should be done to prevent broccoli leaves from turning purple?

The causes of broccoli leave turning purple

Generally, the common cause of purple leaves in plants is phosphorus deficiencies. The leaves of many green plants turn purple when there is phosphorus deficiency in the soil or the absorption of phosphorus by the plant is impaired. Broccoli plants are not excepted from that general theory.

Broccoli leaves may turn purple due to low temperature, overcrowding in the garden, pathogenic attack, improper soil pH, nitrogen deficiency, and phosphorus deficiency. Each of these factors responsible for purple leaves in broccoli will be explained below.

1.   Temperature

Broccoli thrives best at a temperature ranging from 18-23°C. Anything above or below this range can impair broccoli growth. Broccoli thrives well as an indoor-potted plant because they prefer to grow under room temperature.

If the soil is freezing cold, the roots of broccoli plants might not be able to absorb nutrients from the soil. When the absorption of phosphorus nutrients by broccoli roots is altered, it can trigger the leaves of the plants to turn purple.

When you expose broccoli plants to sunlight above their optimum range, it can trigger the release of anthocyanin by the plant. Anthocyanin is a naturally occurring water-soluble pigment in plants with varying colors that depend on soil pH. Based on the soil pH, anthocyanin can release red, purple, blue, or black pigments.


2.   Overcrowding

Broccoli is a heavy feeder vegetable. Vegetables that are categorized as heavy feeders have higher nutrient needs for growth. These types of vegetables usually take longer to reach maturity, especially when they do not have access to sufficient nutrients.

Planting broccoli in a crowded garden will prevent it from absorbing its optimum nutrient requirement for proper growth. Ideally, broccoli should be planted 18-24 inches apart with 36 inches between rows. This will prevent competitive nutrient absorption between the plants.

Pathogenic attack

Blacklegs are infectious disease-carrying pathogens in the soil. They cause purple leaves in broccoli plants by affecting their root systems. The fungal usually infects the plant`s root system and deprives it of absorbing nutrients from the soil.

Blackleg carries fungal disease and hardly affects adult broccoli. Broccoli seedlings are more susceptible to purple leaves caused by pathogens.

3.   Soil pH

The most essential soil analysis is the soil pH test.

Soil acidity plays an essential role in phosphorus absorption by broccoli roots. The higher the soil acidity, the low the phosphorus absorbed by plant roots and vice versa. Broccoli thrives best in well-drained loamy soil with a pH ranging from 6.2-7.5.

Soil PH

4.    Nitrogen deficiency

A nitrogen-deficient broccoli plant will have stunted growth and uniform paling heads. The older leaves will turn purple first before it affects the younger plants.

Nitrogen is an essential nutrient needed for optimum growth in broccoli plants. Nitrogen deficiency can delay protein synthesis in broccoli and alter its photosynthetic activities.

Broccoli plants may break down their own nitrogen when nitrogen is insufficient in the soil. The process usually results in the production of excess carbohydrates, which cause the purple leaves on the plant.

5.    Phosphorus deficiency

Purple leaves in plants are generally caused by phosphorus deficiency. It is either phosphorus is insufficient in the soil, or its absorption is altered in the plant. The leaves of broccoli plants turn purple due to the increased synthesis of anthocyanin.

How to fix broccoli leaves that turn purple

  • Do soil test analysis to determine the soil pH
  • For soil pH lower than 6.2, increase it by adding limestones or dolomites to the soil
  • Compost organic manure should be added to the soil to lower soil pH
  • Maintain the optimal temperature required by the plant. Broccoli plants can receive 6-8 hours of sunlight per day.
  • Diseased broccoli roots can be treated by wetting the plant with a generous amount of potassium permanganate. This should be done when the diseases are caused by fungal attack
  • Water the broccoli plant evenly and consistently. Keep the soil moist but avoid overwatering
  • A drainage system should be created around each of the plants
mature Broccoli

Steps to prevent purple leaves on broccoli

Preventing purple leaves in broccoli plants is essential, especially for the younger seedlings. This is because they are more susceptible to pathogenic attacks. Below are simple practices to prevent purple leaves in broccoli.

  1. Soak each of the seedlings in potassium permanganate before planting them. The compound will induce basic resistance in the seedlings, which will help them to develop resistance to some fungal diseases in the soil. It also helps them to resist environmental stress.
  2. Broccoli plants are heavy feeders. Use organic fertilizer to boost the soil nutrient before and after planting the seedlings.
  3. The soil should be irrigated to prevent waterlogging. Use a drip irrigation system to prevent moisture from spraying on the flowering head.
  4. Maintain an optimum temperature of 18-23°C
  5. Keep the soil pH stable. (6.2-7.5)

Broccoli leaves are nutrient-packed edible vegetables. This has made it one of the choicest home plants in cold temperate regions of the world.

Purple leaves on broccoli are not the end of it. The problem can be fixed.

Purple broccoli is edible and should not be wasted. Identify the cause of the purple color on your broccoli plants. Once you know the cause, follow the steps above to treat the plant.

The major cause of purple leaves in broccoli is phosphorus deficiency, nitrogen deficiency, overcrowding, wrong soil pH, temperature, and pathogenic attack.

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