Blossom end rot is a frustrating problem for tomato growers. You carefully nurture your plants, only to find sunken, black spots developing at the bottom of your ripening fruits. While it looks like a disease, blossom end rot is actually a physiological disorder, not a fungal or bacterial infection. It results from a calcium imbalance in the fruit, often triggered by watering problems or soil nutrient issues. The good news is that blossom end rot can be stopped and even prevented with the right understanding and care. This guide explains the causes, how to recognize early signs, and practical, natural solutions to protect your tomato harvest.
What Is Blossom End Rot?
Blossom end rot appears as a dark, sunken patch at the blossom end — the bottom — of developing tomatoes. It often starts small and water-soaked but enlarges as the fruit grows, becoming black and leathery.
Though blossom end rot is not contagious or caused by pathogens, it damages fruits and reduces yields. If not managed, it can affect large portions of the crop, particularly early fruits on vigorous plants.
What Causes Blossom End Rot?
The underlying cause of blossom end rot is calcium deficiency in the developing fruit. However, even if the soil contains enough calcium, plants may still be unable to absorb and transport it properly.
Common contributing factors include:
- Inconsistent watering: Fluctuations between drought and overwatering stress the roots and hinder calcium uptake.
- Low soil calcium levels: Depleted or imbalanced soils may lack sufficient available calcium.
- Excessive nitrogen fertilization: Rapid vegetative growth can outpace calcium movement to fruits.
- Root damage: Cultivating too close to plants or using aggressive transplanting methods can injure roots.
- Soil pH imbalance: Acidic soils (below pH 6.0) can reduce calcium availability.
Blossom end rot is most common in the early part of the growing season when plants are establishing fruits rapidly.
Early Signs of Blossom End Rot
Catching blossom end rot early can help you take corrective measures before too much damage occurs.
Look for:
- Small, pale or water-soaked spots at the blossom end of immature fruits
- Spots that enlarge, darken, and become sunken over time
- Affected fruits maturing faster than healthy ones
- No unusual spots on leaves or stems (since it is not a systemic disease)
Inspecting fruits regularly during early development is key to early intervention.
How to Stop Blossom End Rot in Tomatoes
Stopping blossom end rot involves correcting the plant’s access to calcium and stabilizing soil moisture.
1. Water Consistently
Fluctuating soil moisture is the leading trigger of blossom end rot.
Best watering practices:
- Water deeply at the soil level 1 to 2 times per week, depending on weather conditions.
- Maintain consistent soil moisture without allowing it to dry out or become waterlogged.
- Use drip irrigation or soaker hoses to avoid overhead watering and keep moisture levels even.
- Mulch around plants with straw, shredded leaves, or grass clippings to conserve soil moisture and regulate soil temperature.
Important: Shallow, frequent watering promotes shallow roots, making plants more vulnerable to stress.
2. Add Calcium If Needed
If soil calcium levels are low, adding a calcium source can help.
Natural calcium sources:
- Crushed eggshells: Add finely crushed eggshells to the planting hole or as a side dressing.
- Bone meal: Slow-release organic fertilizer rich in calcium and phosphorus.
- Agricultural lime: Raises soil pH and adds calcium (only if soil is acidic).
- Gypsum: Provides calcium without altering pH, useful in alkaline soils.
It is important to note that calcium must be taken up by the roots with water, so adding calcium alone is not enough without proper watering.
3. Foliar Calcium Sprays
In some cases, foliar sprays containing calcium can help supply calcium directly to developing fruits.
How to use foliar sprays:
- Apply calcium chloride or calcium nitrate sprays early in fruit development.
- Spray the undersides of leaves where nutrient uptake is more efficient.
- Repeat applications weekly if necessary.
While foliar sprays can help in emergency situations, they are a temporary solution and do not replace the need for good soil and watering practices.
4. Manage Fertilizer Carefully
Over-fertilizing with nitrogen promotes lush foliage growth at the expense of fruit development and calcium transport.
Fertilization tips:
- Use balanced fertilizers with moderate nitrogen content (look for products with NPK ratios like 5-10-10).
- Avoid quick-release synthetic fertilizers that cause sudden spurts of leafy growth.
- Feed plants based on their actual growth needs, not a fixed schedule.
Slow, steady plant growth supports better calcium distribution to fruits.
5. Protect Plant Roots
Healthy roots are critical for calcium uptake.
Tips to protect roots:
- Avoid deep digging or cultivating close to tomato plants.
- Handle transplants carefully to avoid damaging young roots.
- Apply mulch to protect roots from temperature extremes and moisture fluctuations.
Minimizing root stress leads to stronger plants and better fruit quality.
How to Prevent Blossom End Rot
Prevention is the best approach because once a fruit shows signs of blossom end rot, the damage cannot be reversed on that fruit (though the plant can still be saved).
Steps to prevent blossom end rot:
- Test and amend your soil before planting.
- Plant tomatoes in well-drained soil with good organic matter content.
- Maintain even soil moisture from the moment fruits begin to form.
- Choose tomato varieties known for blossom end rot resistance if possible.
- Space plants adequately to ensure good air circulation and reduce competition for water and nutrients.
Planning and preventive care produce healthier plants with stronger fruit development.
Is It Safe to Eat Tomatoes with Blossom End Rot?
Yes, tomatoes affected by blossom end rot are still safe to eat. Simply cut away the damaged portion and use the rest of the fruit if it is otherwise healthy. However, fruits with extensive damage may have poor texture and flavor.
Blossom end rot affects only the fruit’s appearance and quality, not its safety.
FAQs About Blossom End Rot in Tomatoes
Can blossom end rot spread from fruit to fruit?
No, blossom end rot is not contagious. Each fruit is individually affected based on the plant’s calcium transport and watering conditions.
Will adding crushed eggshells to the soil immediately fix blossom end rot?
Eggshells release calcium slowly over time and are best used as a long-term soil amendment. They do not provide an immediate fix for developing fruits.
Should I remove fruits with blossom end rot?
It is a good idea to remove severely affected fruits so the plant can redirect energy into producing healthy new fruits.
How long does it take for blossom end rot to clear up?
Once soil moisture is stabilized and calcium availability improves, new fruits usually grow without symptoms. Improvement can be seen within a few weeks.
Does blossom end rot only affect tomatoes?
No, blossom end rot can also affect peppers, squash, zucchini, and eggplant, all of which have similar calcium and moisture needs.