Tomatoes Turning Black

If you’ve ever seen your beautiful tomatoes turning black, you know how disheartening it can be. This common garden problem can ruin your harvest, but understanding the causes is the first step to prevention.

It’s usually a sign of a disorder or disease, not necessarily a pest. The good news is that with the right knowledge, you can stop it from happening. Let’s look at the main reasons your tomatoes develop those ugly black spots and what you can do about it.

This specific symptom has a few likely culprits. The most common is a physiological condition called blossom end rot. Other causes include fungal diseases and even sunscald. Identifying which one you’re dealing with is crucial for the correct fix.

Blossom End Rot: The Main Culprit

Blossom end rot (BER) is not a disease, but a calcium deficiency in the developing fruit. It starts as a small, water-soaked spot at the blossom end (the bottom) of the tomato. The spot enlarges, turns dark brown or black, and becomes leathery.

Key things to know about BER:

It affects green, developing fruit, not mature ones.
The rest of the fruit often ripens normally, but the black spot rots quickly.
It’s most common on the first fruits of the season.
The problem isn’t always a lack of calcium in the soil, but the plant’s inability to take it up.

How to Fix and Prevent Blossom End Rot

Since inconsistent watering is the primary cause, your goal is to maintain even soil moisture. Here’s your action plan:

Water Deeply and Regularly: Tomatoes need 1-2 inches of water per week. Water at the base, not the leaves, and use mulch to retain moisture.
Test Your Soil: A soil test can confirm calcium levels. If truly deficient, add gypsum (calcium sulfate) or crushed eggshells to the planting hole before next season.
Avoid Excessive Nitrogen: High-nitrogen fertilizers promote rapid leaf growth at the expense of fruit, worsening calcium uptake. Use a balanced fertilizer.
Maintain Soil pH: Soil that is too acidic or alkaline locks up calcium. Aim for a pH of 6.5-6.8 for optimal nutrient availability.

Fungal Diseases That Cause Blackening

If the black spots appear on the sides or top of the fruit, or on leaves and stems, you’re likely dealing with a fungus. Two common ones are anthracnose and late blight.

Anthracnose

This fungus shows up on ripe or ripening fruit as small, sunken, circular spots. They start watery and then turn dark black. It spreads splashed by water and thrives in warm, wet weather.

Prevention: Use mulch to prevent soil from splashing onto fruit. Ensure good air circulation by spacing plants properly. Water in the morning so leaves dry quickly.
Control: Remove and destroy infected fruit immediately. Use a fungicide labeled for anthracnose on tomatoes as a last resort.

Late Blight

This is a serious, fast-moving disease. It causes irregular, greasy-looking gray or brown lesions on leaves that quickly spread. Fruit develop firm, brownish-black lesions. Cool, wet weather promotes it.

Prevention: Choose resistant varieties. Avoid overhead watering completely.
Control: Remove and bag infected plants immediately—do not compost. Fungicides can be protective but must be applied before infection occurs.

Other Causes: Sunscald and Pest Damage

Sometimes the cause is environmental. Sunscald happens when exposed fruit, often after leaf loss from disease, gets too much direct sun. It creates a white or yellow patch that turns black and papery.

Prevent it by proper pruning (don’t overdo it) and managing leaf diseases to maintain protective foliage. Some pests, like stink bugs, inject a toxin that causes hard, white or yellow spots under the skin that can darken.

Your Step-by-Step Prevention Plan

An ounce of prevention is worth a pound of cure, especially in the garden. Follow this seasonal guide to keep your tomatoes healthy from start to finish.

Before Planting (Planning Stage)

Choose Resistant Varieties: Look for codes like “BER” or “LB” (Late Blight) resistance on plant tags or seed packets.
Prep the Soil: Get a soil test. Amend with compost to improve texture and water retention. Adjust pH if needed.
Select the Right Location: Pick a spot with full sun (6-8 hours) and excellent air circulation.

At Planting Time

Space Properly: Give plants room (usually 24-36 inches apart) for air to move. This reduces fungal pressure.
Plant Deep: Bury the stem up to the first set of leaves. This encourages a strong, extensive root system for better water uptake.
Add Calcium: If you’ve had BER before, add a handful of gypsum or crushed eggshells to the planting hole.
Install Supports: Put cages or stakes in now to avoid damaging roots later.

During the Growing Season

Mulch, Mulch, Mulch: Apply 2-3 inches of straw or wood chips. This keeps soil moisture even and prevents soil-borne diseases from splashing up.
Water Wisely: Use a soaker hose or drip irrigation. Water deeply 1-2 times a week rather than a little every day.
Fertilize Correctly: Use a balanced, slow-release fertilizer or one formulated for tomatoes. Avoid high-nitrogen mixes once flowering begins.
Monitor Regularly: Check your plants weekly for early signs of trouble. Remove any diseased leaves or fruit immediately.
Prune for Airflow: Prune off the lower 6-12 inches of leaves to improve circulation and remove the first leaves that often get fungal spores.

What to Do With Affected Tomatoes

If you catch blossom end rot early on a large fruit, you can sometimes cut off the black portion and the rest is edible. However, if its a fungal disease like anthracnose, the damage often goes deeper than it looks. It’s safest to discard diseased fruit in the trash, not your compost pile, to prevent spreading pathogens.

For sunscalded fruit, you can cut away the affected tissue if it hasn’t become moldy. The key is to remove problem fruit from the garden promptly to break the cycle of infection.

FAQ: Tomatoes Turning Black

Q: Can you eat tomatoes with black bottoms?
A: If it’s purely blossom end rot, you can cut off the black part and the rest is fine to eat. If it’s mushy or moldy from a fungal disease, it’s best to toss it.

Q: Does Epsom salt help with blossom end rot?
A: No. Epsom salt is magnesium sulfate. Blossom end rot is a calcium issue. Adding Epsom salt can actually make the problem worse by competing with calcium uptake.

Q: How do I add calcium to my tomato plants quickly?
A: For a quick foliar spray, you can use calcium chloride or calcium nitrate. However, this is a temporary fix. Improving consistent watering is the real long-term solution for BER.

Q: Why are my cherry tomatoes turning black on top?
A> This is less likely to be BER (which is on the bottom). It could be sunscald if they’re overexposed, or a fungal disease like anthracnose. Check the leaves for spots to help diagnose.

Q: Will crushed eggshells help this season?
A: Crushed eggshells decompose very slowly. They are a great long-term soil amendment but won’t provide immediate calcium for plants already struggling. Add them to the soil in the fall for next year’s garden.

Seeing your tomatoes turning black is frustrating, but it’s rarely a hopeless situation. In most cases, especially with blossom end rot, you can correct the problem for future fruit on the same plant. Focus on the fundamentals: consistent watering, proper soil preparation, and good garden hygiene. By taking these proactive steps, you can look forward to a healthy, bountiful harvest of perfect, unblemished tomatoes.