Watermelon Growing

Watermelon Blossom End Rot: A Common Problem, Solved

Watermelons are a summertime staple, but nothing ruins a picnic faster than a rotten watermelon. If you’ve ever had a watermelon with a black bottom, you’ve likely encountered blossom end rot.

What is Watermelon Blossom End Rot?

Watermelon blossom end rot is a condition that causes the bottom of the watermelon to turn black and leathery. It’s not caused by a pathogen, but rather by a lack of calcium in the fruit.

Why Do Watermelons Get Blossom End Rot?

Calcium is essential for the proper development of fruits, but it doesn’t move through the plant very well. If the soil doesn’t have enough calcium, or if the plant is unable to absorb it, the fruits will be deficient.

Rapidly growing fruits, like watermelons, need a lot of calcium. If the calcium supply is low, the cells in the blossom end of the fruit will collapse, causing the black, leathery lesion.

Factors that Contribute to Blossom End Rot

• Fluctuating water levels: Water is necessary to move calcium to the fruits, but too much water can lead to poor drainage and root problems.
• Excessive nitrogen fertilizer: Too much nitrogen can promote vine growth at the expense of fruit development.
• Wrong type of fertilizer: Ammonium-based fertilizers can bind calcium in the soil, making it unavailable to the plants.

How to Prevent Watermelon Blossom End Rot

• Maintain a consistent watering schedule: Water your melons regularly, but avoid overwatering. The soil should be moist, but not soggy.
• Test your soil pH: The ideal soil pH for watermelons is between 6.5 and 6.7. If your soil is too acidic (below 5.5), you’ll need to amend it with lime to raise the pH.
• Fertilize with a balanced fertilizer: Choose a fertilizer that is specifically formulated for watermelons. Avoid fertilizers with high levels of nitrogen.
• Add mulch: Mulch helps to retain soil moisture and regulate soil temperature. This can help to prevent blossom end rot.

How to Treat Watermelon Blossom End Rot

If your watermelons have already developed blossom end rot, there’s not much you can do to save the affected fruits. However, you can take steps to prevent the problem from spreading:

• Remove the damaged fruits from the vine: This will encourage the plant to produce new flowers.
• Check the soil around your vines: Make sure the soil is not too wet or too dry. Adjust your watering schedule accordingly.
• Amend the soil: If your soil is acidic, add lime to raise the pH. If your soil is compacted, add compost to improve drainage.

Additional Tips for Growing Healthy Watermelons

• Choose resistant varieties: Some watermelon varieties are more resistant to blossom end rot than others. Ask your local nursery for recommendations.
• Rotate your crops: Planting watermelons in the same location year after year can deplete the soil of calcium. Rotate your crops to avoid this problem.
• Avoid overwatering: Overwatering is one of the most common causes of blossom end rot. Water your melons regularly, but avoid getting the leaves wet.

By following these tips, you can help to prevent and treat watermelon blossom end rot, and enjoy delicious, healthy watermelons all summer long.