Being an avid fruit eater and especially appreciating the taste and health benefits of blueberries, I have just finished planting a couple of blue berry bushes myself that are doing very well. However, I have learnt and am still learning a few things along the way when it comes to growing blueberries. In this article I will answer the question: Why Are My Blueberry Leaves Turning Red? Along with advice on how to prevent and fix the problem.
Blueberry leaves turn red in the growing season because of either a phosphorus deficiency, magnesium deficiency, bacterial disease, fungal disease, nutrient problems or cold exposure. However, if the blueberry leaves are turning red in the fall, then it is a natural response to the colder weather. There is no problem.
During autumn or fall (end of September to end of December in the United States) the blueberry bush (Vaccinium corymbosum) will naturally have red leaves. This is normal, however during Spring and Summer the leaves should be a green color. If they are red during the Spring and Summer then it is one or more of the problems listed above.
It might be of benefit for you to also check out the post: When Are Blueberries In Season. This article lists every blueberry season in every State along with the best varieties to grow in each State.
So, now we need to look at each one individually and work out which is causing your leaves to turn red and how to fix the problem.
1. Phosphorous Deficiency
Phosphorous Deficiency in blueberry plants will often show with leaves having a red tinge due to anthocyanins (purple pigments) accumulation. The plant may also appear stunted in growth. Phosphorous deficiency can also cause a purple coloration in the leaves.
You can fix this problem by adding more phosphorous to the soil with superphosphate, monoammonium phosphate, or diammonium phosphate. However, it is recommended using rock phosphate as it releases phosphorous more slowly. Too much phosphorous in the form of chemical superphosphate can be detrimental to the uptake of other necessary nutrients.
Another way to naturally put phosphorous into your soil is to use a good organic liquid seaweed. It contains a good balance of phosphorus along with magnesium, nitrogen, potassium, iodine, calcium, macro and micro-nutrients, vitamins, amino acids, and other nutrients and trace minerals.
Another limiting factor of phosphorous uptake is soil acidity. Blueberries need an acidic soil of between pH 4.5 – pH 5.0 to thrive (although I have read that pH 4.3 – pH 4.8 is optimal). If the pH is greater than 5.2 it becomes too alkaline and the blueberry cannot take up the nutrients from the soil leading to deficiencies in phosphorous and many other nutrients.
To know your soil pH you can buy some pH test strips from your local nursery or gardening centre to get a rough idea of weather you have alkaline or acidic soil. Or better still you can get a sample of your soil sent to a soil testing laboratory to get an accurate pH reading.
To fix soil acidity you can use:
- Coffee grounds
- Pine needles
- Lemon Juice
I like to scratch some sulphur into the ground around the base and roots of the blueberry bush. This can lower the soil pH by about 0.5 or more.
Another trick I have used is to juice the skins of lemons (or whole lemon if you prefer) in a juicer then dilute with water and pour it around the base of the blueberry plant, making sure you don’t pour it over the leaves as it can burn and kill them. Doing this regularly will lower the soil pH and make it more acidic.
For the lemon juice solution, you will need to mix 2 tablespoons of lemon juice in 1 gallon of water and then pour the mixture onto the soil around the base of the blueberry plant. Avoid the leaves, even when the mixture is diluted, as it can cause the leaves to shrivel, making it difficult for the plant to perform photosynthesis.
Solution: To prevent this problem from happening in the first place make sure your soil pH is between the range of 4.3 pH to 5.0 pH with optimal range between 4.3 pH and 4.8 pH. Use either rock phosphate on the soil before planting or a good organic liquid seaweed.
2. Magnesium Deficiency
Magnesium deficient blueberry plants will have older leaves with interveinal necrosis or edges starting red and turning brown and is common in acid soils. The interveinal reddening occurs due to a reduction in chlorophyll production. Symptoms begin as a yellowing and then progresses to a bright red.
Solution: Magnesium deficiency can be treated by the application of Epsom Salts (magnesium sulphate) or hydrated dolomitic lime. However dolomitic lime is alkaline so should only be used if the soil pH is below 4.3
3. Fungal Diseases
There are many fungal diseases that can affect the blueberry plant. We will discuss a couple of them and how to treat the infection.
Phomopsis Twig Blight
If your blueberry plant has phomopsis then the Infected buds will become brown and die. A brown lesion will appear on the twig around the bud, and spreads as the fungal disease progresses.
Solution: During the season where your blueberries are not fruiting you will need to prune and destroy the infected twigs. You might also want to avoid overhead irrigation in order to limit spread of the pathogen.
A few resistant varieties are available, including Bluetta and Elliott.
Powdery mildew first causes a yellow discoloration on the upper leaf surfaces eventually developing into red spots.
Disease development occurs in warm, dry weather, so powdery mildew symptoms appear in mid-summer.
Solution: Generally powdery mildew is not so severe to warrant a fungicide. However, if the blueberry leaves are affected, you can use fungicides such as Orbit, Tilt or Quash.
4. Bacterial Diseases
The bacteria Xylella fastidiosa is responsible for ‘Blueberry leaf scorch’. Symptoms of infection include burnt edge of older leaves which turn red and eventually die, stem yellowing, and dieback.
Solution: Remove and destroy infected plants to prevent infection spreading.
5. Nutrient Problems
Lack of nutrients in the soil can cause many problems including red and purple tinges to the leaves. The most common nutrient deficiencies causing red leaf problems are phosphorous and magnesium. To correct these problems, as mentioned above, use an organic liquid seaweed fertilizer along with potash of sulphate.
Its important to correct the soil pH by adding sulphur to the ground or lemon juice if the soil is too alkaline.
Many other nutrient deficiencies can occur such as iron, potassium and calcium but they too can be fixed with a good organic liquid seaweed fertilizer.
6. Cold Exposure
When the weather cools down during autumn and winter it is usual for the leaves to have a red color to them. However, during the spring and summer growing season the leaves should be a green color.
If the blueberry leaves remain red during the growing season, then there is an underlying problem caused by one of the deficiencies or diseases listed above.
What Is The Best Fertilizer For Blueberry?
The best fertilizer for blueberry is organic liquid seaweed and fish, along with potash of sulphur for setting the fruit.
If the soil is too alkaline then using lemon juice that has been diluted or some sulphur will help to lower the soil pH.
How Often Should I Water Blueberry Bushes?
Blueberry plants will need 25-50mm water per week during the fruiting season. Younger plants will require more water needs and they can be easily damaged by under or over watering. Blueberry plants can be stressed by short periods of one to three weeks without rain.
For more information on caring for your blueberry bush please take a look at our article: How To Care For A Blueberry Bush where an organic blueberry farmer provides tips on how best to take care of your blueberry plants.
 Acid Soils in Hawaii
 SFGATE: Can I Feed Lemon Juice to Plants?
 University of Florida: Nutrition and Fertilization Practices for Southern Highbush Blueberry in Florida
 Ohio State University Extension: Phomopsis Twig Blight of Blueberry
 PennState Extension: Blueberry Disease – Powdery Mildew
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