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Blossom end rot – not caused by a pesky insect or a disease, but it is caused by adverse growing conditions. Although it most commonly occurs in tomatoes, it also appears on squash, peppers, cucumbers, zucchini and melons.
What Causes Blossom End Rot?
Blossom end rot occurs in plants when there isn’t enough calcium in the fruits on the plant. All plants require calcium so that they develop healthily. When plants can’t get enough calcium from the soil, the blossom end of the fruit rots and breaks down. Blossom end rot most commonly begins when the growing season starts out particularly wet and becomes dry once the fruit is set. While it’s uncommon for soil or growing bags to lack calcium, for the calcium to be absorbed by the roots and circulated around the plant, there needs to be a sufficient and consistent flow of water. Plants that are in a limited space, such as a pot or a growing bag, are most likely to suffer from blossom end rot. The fruits are a long way from the roots of the plant and find it difficult to compete with the leaves for the calcium.
Symptoms of Blossom End Rot
Blossom end rot only attacks the fruit on a plant. The plant itself and the leaves appear perfectly normal. It shows itself on the bottom end of the fruit as a circular patch that is a greeny brown or black. The size of the patch varies greatly, but between 1 and 2.5cm is normal. As the patch of blossom end rot on the fruit gets larger, it becomes sunken, giving it a flat appearance.
Prevention and Control
Unfortunately, there is nothing that can be done for fruits that are already affected by blossom end rot. You can, however, prevent other fruits from becoming affected.
- Test the pH of your soil. Fruiting plants do well with a pH soil level of 6.2 to 6.8. For those plants with blossom end rot the level should be 6.5 to 6.8. This frees up the calcium in the soil.
- Lime is a great way of ensuring the pH soil level is correct to prevent blossom end rot. Lime contains calcium and should be added to the top 12 inches of soil. Add crumbled eggshells to the soil to maintain the levels of calcium in the soil.
- Don’t fertilize your plants too much. This ties up the calcium in the soil.
- Keep the levels of moisture in the soil at a constant level. When the weather is very dry and hot, water two or three times a day to a level of 6 inches deep (assuming you’re using feeders on some description), according to the Royal Horticultural Society.
- In cold climates, warm the soil before placing plants in the soil. Soils that are particularly cold limit the nutrient uptake.
- Use watering cones to help the water get deep in the soil.
- Add 3 inches of organic mulch around your plants. This helps your plants retain moisture.
- Keep your plants healthy. Like many other plant diseases, blossom end rot is more likely to attack weaker or unhealthy plants, so make sure you do your best to control pests. Aphids and tomato hornworms are particularly damaging to tomato plants, so check out our guide on controlling aphids naturally or our tomato hornworm pest profile.
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