Blossom End Rot on Tomatoes: Causes, Treatment & Prevention

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Blossom end rot is one of the most common problems tomato growers face. It shows up as a dark, sunken spot on the bottom (blossom end) of developing fruit, sometimes when the fruit is still green, other times just as it begins to ripen. While it looks like a disease, blossom end rot isn’t caused by fungi or bacteria. It’s a physiological disorder linked to calcium deficiency in the fruit, often triggered by uneven watering or other growing conditions. Learn more about how to properly water tomatoes to avoid this common problem.

The good news? You can’t fix fruit that already has it, but you can take steps right away to prevent it from affecting the rest of your crop.

WHAT IS BLOSSOM END ROT?

Blossom end rot shows up as dark, sunken spots on the blossom end of tomatoes and other fruits in the same family. Because it isn’t caused by insects or disease organisms, fungicidal and insecticidal sprays won’t help (Missouri Botanical Garden).

• Appears as water-soaked spots that turn dark brown or black
• Affects tomatoes most often, but can also occur on peppers and eggplant
• Typically shows up on the first flush of fruit, though later fruit can be affected too
• Does not spread from fruit to fruit, each one develops symptoms individually

WHAT CAUSES BLOSSOM END ROT?

Blossom end rot happens when developing fruit doesn’t get enough calcium during cell formation. The soil may contain calcium, but the plant can’t always move it into the fruit. Common causes include:

• Inconsistent soil moisture: Dry soil followed by heavy watering or rain disrupts calcium uptake.
• Low soil pH: Acidic soil (pH below 6.2) makes calcium less available.
• Excess nitrogen: Promotes rapid foliage growth, diverting calcium away from fruit.
• Root damage: Cultivating too deeply around plants can damage roots and limit calcium uptake.

Tip: A simple soil test can tell you your pH and calcium levels.

Photo by: Photo by: Mila Makhova

Quick Tips

• Check soil moisture daily during hot weather
• Mulch early in the season to regulate soil moisture
• Use balanced fertilizer; avoid sudden nutrient spikes
• Test soil pH yearly and amend if needed
• Choose tomato varieties less prone to blossom end rot (smaller-fruited types are often less affected)

HOW TO PREVENT BLOSSOM END ROT

You can’t fix fruit that already has blossom end rot, but these steps will help prevent it from spreading to future fruit.

1. Keep soil moisture even

• Water deeply and consistently, 1 to 2 inches per week is typical.
• Mulch with straw, leaves, or compost to help retain moisture.
• Avoid letting soil dry out completely between waterings.

2. Check soil pH and calcium

• Test soil pH (target range: 6.2 to 6.8) and calcium levels before planting.
• Apply lime or gypsum only if recommended by your soil test.

3. Fertilize carefully

• Avoid high-nitrogen fertilizers, especially early in the season.
• Choose a balanced fertilizer to encourage steady growth.
• Tip: When fertilizing, opt for nitrate-based nitrogen rather than ammonium forms, as ammonium can compete with calcium uptake and increase the chance of blossom end rot. (University of Wisconsin Plant Disease Diagnostics Clinic)

4. Use foliar calcium sprays (temporary help)

• Sprays with calcium chloride or calcium nitrate can help new fruit but won’t fix existing damage.
• Apply according to label directions and combine with proper watering practices.

5. Remove affected fruit

• Damaged fruit will not recover; remove it to redirect energy into healthy growth.

FREQUENTLY ASKED QUESTIONS

Does blossom end rot affect peppers and eggplant?

Yes. Both peppers and eggplant are in the same plant family as tomatoes (Solanaceae) and can develop the same dark, sunken spots when calcium uptake is disrupted. Prevention and treatment methods are identical: consistent watering, balanced soil fertility, and proper pH.

Can you eat tomatoes with blossom end rot?

Yes, simply cut away the damaged portion. The rest of the fruit is safe to eat, though the texture and flavor may be affected near the damaged area.

Will Epsom salt fix blossom end rot?

No. Epsom salt adds magnesium, not calcium, and can actually make blossom end rot worse by interfering with calcium uptake. Use lime, gypsum, or calcium sprays instead, but only if a soil test shows calcium is low.

Will the problem spread to healthy fruit?

No. Blossom end rot is not contagious; each fruit develops symptoms on its own. Once conditions are corrected, future fruit will form normally.

How fast can blossom end rot be fixed?

Existing spots won’t heal, but new fruit can be symptom-free within two to three weeks if soil moisture and calcium levels are corrected.

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