Seeing your tomatoes rotting on the vine is a frustrating end to a season of hard work. This problem of tomatoes rotting on the vine – slowly decaying in sunlight – is common, but it’s also preventable with the right knowledge.
That soft, sunken spot that starts at the blossom end of the fruit isn’t a disease in the traditional sense. It’s a physiological disorder, meaning it’s caused by how the plant functions. Understanding the “why” is the first step to saving your harvest.
Tomatoes Rotting On The Vine – Slowly Decaying In Sunlight
This specific type of rot is called Blossom End Rot (BER). It begins as a small, water-soaked spot at the bottom of the tomato, opposite the stem. This spot enlarges, turns dark brown or black, and becomes leathery. It often happens just as the fruit begins to ripen, making it especially disheartening.
What Really Causes Blossom End Rot?
Contrary to popular belief, it’s not caused by a fungus or bacteria you can spray. The primary cause is a calcium deficiency in the developing fruit. However, the issue is rarely a lack of calcium in your soil.
Most often, the plant cannot move enough calcium to the fruit due to environmental stresses. Calcium moves with water in the plant, so anything that disrupts steady water uptake is the real culprit.
The Main Contributing Factors
- Inconsistent Watering: Fluctuating between very wet and very dry soil is the biggest trigger. The plant’s water (and calcium) transport gets disrupted.
- Rapid Early Growth: Lush growth from too much nitrogen fertilizer can outpace the plant’s ability to supply calcium to the fruit.
- Root Damage: Cultivating too close to the plant or pest damage can harm the roots, limiting water and nutrient uptake.
- Soil pH Issues: Very acidic or alkaline soil can lock up calcium, making it unavailable to the plant even if it’s present.
- Cold or Waterlogged Soil: Cool early-season temperatures or soggy soil can stunt root function.
Your Step-by-Step Prevention Plan
Preventing blossom end rot is about managing the plants environment. Follow these steps from planting onward.
1. Before You Plant: Soil Preparation
Start with a soil test. This tells you your soil’s pH and calcium levels. The ideal pH for tomatoes is between 6.5 and 6.8.
- If your soil is acidic (low pH), add garden lime according to test recommendations. This adds calcium and adjusts pH.
- If your pH is good but calcium is low, add gypsum (calcium sulfate). It adds calcium without altering pH.
- Mix in plenty of compost. It improves soil structure and helps retain consistent moisture.
2. The Right Way to Water
Consistency is everything. Your goal is soil that feels like a wrung-out sponge—moist, not soggy.
- Water deeply and less frequently, rather than shallow daily sprinkles.
- Provide 1-1.5 inches of water per week, including rainfall. Use a rain gauge.
- Water at the base of the plant, not the leaves, to avoid foliar diseases.
- Mulch, mulch, mulch! A 2-3 inch layer of straw, shredded leaves, or wood chips keeps soil moisture even and prevents rapid drying.
3. Smart Fertilizing Practices
Go easy on high-nitrogen fertilizers (the first number in N-P-K). They promote leafy growth at the expense of fruit.
- Use a balanced fertilizer or one formulated for tomatoes.
- Consider adding a handful of bone meal (high in calcium and phosphorus) to the planting hole.
- If you see symptoms early, you can try a foliar spray of calcium chloride or calcium nitrate. This is a quick fix, not a cure, as calcium doesn’t move well from leaves to fruit. It’s better for prevention on later fruit.
4. Choosing Resistant Varieties
Some tomato varieties are more susceptible than others. Plum and paste tomatoes (like Roma) often have more issues. Larger beefsteak types can be prone too.
If BER is a recurring problem in your garden, try more resistant varieties. Many modern hybrids and even some heirlooms are bred for better calcium uptake. Cherry tomatoes are rarely affected.
What to Do When You See Rot
Don’t panic. Act quickly to save the rest of your crop.
- Remove Affected Fruit: Pick off any tomatoes with signs of rot. They will not recover and can attract other pests.
- Check Your Watering: Immediately assess your soil moisture and correct your watering schedule. This is the most important step.
- Apply Mulch: If you haven’t already, add mulch now to stabilize soil conditions for the remaining fruit.
- Do a quick soil check. Is it waterlogged? Bone dry? Adjust accordingly.
The fruit that sets after you correct the problem will likely be just fine. The disorder is not systemic in the plant.
Common Myths About Tomato Rot
Let’s clear up some misinformation you might here.
- Myth: “Adding eggshells to the hole will fix it.” Crushed eggshells decompose too slowly to help the current season’s plants. They are a long-term soil amendment.
- Myth: “It’s contagious.” Blossom End Rot does not spread from plant to plant like a blight.
- Myth: “All rot on tomatoes is the same.” Sunscald, fungal diseases, and insect damage can look different. BER is always at the blossom end and has that characteristic leathery, sunken spot.
Other Sun-Related Tomato Troubles
While BER is the classic “rot in sunlight,” other issues can look similar.
Sunscald
This appears as a white, blistered patch on the side of the fruit facing the sun. It happens when fruit is overexposed to direct, intense sunlight, often after defoliation from disease or pruning too heavily. The patch can become papery and invite secondary rot.
Prevention: Maintain good leaf cover to shade fruit. Avoid excessive pruning, especially in hot weather.
Anthracnose
This is a true fungal disease. It causes small, circular, sunken spots that can appear anywhere on the ripe fruit. The spots darken and may have concentric rings. It spreads in warm, wet weather.
Prevention: Water at the soil level, rotate crops yearly, and remove infected plant debris at season’s end.
End of Season Care
To break the cycle for next year, good garden cleanup is essential.
- Remove all tomato vines and any fallen, rotten fruit from the garden. Don’t compost material from diseased plants.
- Test your soil in the fall so you have time to amend it before spring.
- Plan your garden layout to rotate tomatoes to a different bed next year if possible.
FAQ: Your Tomato Rot Questions Answered
Can you eat a tomato with Blossom End Rot?
You can cut off the rotten portion and eat the rest of the tomato. The unaffected part is safe and often tastes normal. Just make sure no secondary mold has grown in the affected area.
Does Epsom salt help with blossom end rot?
No. Epsom salt is magnesium sulfate. Adding it can actually make the problem worse by competing with calcium uptake. It is not a cure for calcium-related issues.
How do I add calcium to my tomato plants quickly?
For a fast supplement, use a liquid calcium product as a foliar spray or soil drench, following label instructions. Remember, the real fix is correcting watering habits so the plant can absorb calcium already in the soil.
Why are my tomatoes rotting on top instead of the bottom?
Rot on the top or sides is likely sunscald or a fungal disease like anthracnose. Examine the conditions—intense sun exposure or wet foliage are clues.
Will overwatering cause tomatoes to rot?
Yes, absolutely. Waterlogged soil suffocates roots, preventing them from taking up calcium and water properly. This leads to the same inconsistency that triggers BER. Good drainage is as important as regular watering.
Watching tomatoes rotting on the vine is tough, but now you know it’s a solvable problem. Focus on consistent soil moisture from planting to harvest. Test your soil, water deeply, and mulch well. By managing the plants environment, you’ll give your tomatoes the best chance to develop fully, turning that anticipation into a bounty of healthy, sun-ripened fruit for your table.