Brassica oleracea Red Kale Yellow Leaves - Causes & Fixes

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Nitrogen Deficiency

Nitrogen is a mobile nutrient in kale, so the plant relocates it from older leaves to newer growth when supply is low. This results in characteristic chlorosis (yellowing) starting with the bottom-most mature leaves.

Very Common

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How to confirm: Check if the yellowing is progressing strictly from the oldest, lowest leaves upward toward the crown.

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shopping_cart Recommended Products

1 Apply a nitrogen-rich organic fertilizer to replenish the soil nutrients and stop the yellowing of older leaves.

Back to the Roots Blood Meal & Gypsum (4 Pack)

Organic Fertilizer

$40

Out of Stock

2 Incorporate a balanced organic soil amendment like worm castings to provide long-term nutrient availability.

Back to the Roots Organic Worm Castings 5lb

Worm Castings

$17

In Stock

3 Monitor soil moisture levels to ensure the nitrogen is being effectively transported to the roots.

GROWIT Soil Moisture Meter - Blue

Water Meters

$12

In Stock

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Overwatering and Root Hypoxia

Excessive soil moisture displaces oxygen in the root zone, causing the roots of Red Kale to suffocate. This prevents the uptake of nutrients, leading to general leaf yellowing and eventual wilting.

Very Common

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How to confirm: Stick your finger two inches into the soil; if it feels saturated or muddy, reduce watering frequency.

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1 Immediately stop watering and allow the soil to dry out significantly to restore oxygen to the root zone.

GROWIT Soil Moisture Meter SMM-V3

Water Meters

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2 Check the drainage of your container; if the soil remains saturated, repot the kale in a well-draining medium like Espoma Organic Potting Soil Mix to prevent further root rot.

Espoma Organic Potting Soil Mix

15.1 L

$22

In Stock

3 Once the plant stabilizes, apply a balanced liquid fertilizer to help recover from nutrient uptake inhibition.

FoxFarm Grow Big Liquid Plant Food 1 Quart

0.9 L • 1 pcs

$30

In Stock

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Magnesium Deficiency

In Brassicas, magnesium deficiency often presents as interveinal chlorosis, where the tissue between the veins turns yellow while the veins remain dark green.

Common

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How to confirm: Examine if the yellowing is specifically occurring between the leaf veins on older leaves.

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shopping_cart Recommended Products

1 Apply a magnesium-rich supplement to the soil to quickly address the interveinal chlorosis.

FoxFarm Bush Doctor Cal Mag Liquid Supplement 1 Pint

0.5 L • 1 pcs • Organic

$22

In Stock

2 Monitor soil moisture levels using a moisture meter to ensure consistent hydration, as water stress can exacerbate nutrient deficiencies.

GROWIT Soil Moisture Meter - Blue

Water Meters

$12

In Stock

3 Ensure the plant is receiving adequate nutrition by using a balanced liquid fertilizer to support overall plant vigor.

FoxFarm Grow Big Liquid Plant Food 1 Quart

0.9 L • 1 pcs

$30

In Stock

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Temperature Stress (Heat)

Red Kale is a cool-season crop; exposure to temperatures consistently above 80°F (27°C) can cause physiological stress, leading to rapid yellowing and loss of anthocyanin (red) pigment.

Common

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How to confirm: Monitor local nighttime temperatures and check if the yellowing coincided with a recent heatwave.

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shopping_cart Recommended Products

1 Relocate the kale to a cooler, shaded area or use a shade cloth to protect the leaves from direct, intense sunlight and high temperatures.

2 Monitor soil moisture levels closely to ensure the plant remains hydrated during heat waves, using a moisture meter to prevent dehydration.

GROWIT Soil Moisture Meter - Blue

Water Meters

$12

In Stock

3 Apply a liquid seaweed fertilizer to help the plant recover from heat-induced physiological stress and boost nutrient uptake.