What Is Blossom End Rot?

Blossom end rot is a common tomato problem that appears as a dark brown or black spot on the bottom of the fruit, opposite the stem.

The affected area may look sunken, leathery, or rotten, while the rest of the plant may still look healthy.

Despite the name, blossom end rot is usually not a contagious disease. It does not spread from plant to plant like a fungus or bacterial infection.

Instead, it is a plant stress issue connected to calcium not reaching the developing fruit consistently.

What Causes Blossom End Rot?

Blossom end rot is connected to calcium, but that does not always mean your soil has no calcium.

In many gardens, there may be enough calcium in the soil already. The issue is that the plant is not moving calcium into the fruit consistently.

That can happen when the plant goes through moisture swings, especially during hot weather.

Common triggers include:

• Inconsistent watering
• Soil drying out too much between waterings
• Overwatering or waterlogged soil
• Root stress
• Hot, dry, windy weather
• Too much fast leafy growth from over-fertilizing

That is why blossom end rot often shows up during summer, especially on the first tomatoes of the season. For more summer garden stress tips, see our guide on how to help your garden beat the heat.

What Should You Do First?

Start by removing the affected fruit.

The damaged tomato will not heal, and removing it helps the plant put energy toward healthy fruit that is still growing.

Then focus on the biggest improvement you can make: keeping soil moisture more consistent.

The goal is not necessarily to water more.

The goal is to avoid big swings between too dry and too wet.

Consistent Moisture Comes Next

To help prevent blossom end rot, try to keep your tomato plants evenly watered.

A few helpful steps:

• Water deeply and consistently
• Check the soil a couple inches down before watering again
• Avoid letting containers or raised beds dry out completely
• Add mulch to help hold moisture and keep soil cooler
• Avoid disturbing roots around the plant
• Be careful not to over-fertilize with nitrogen

Mulch can be especially helpful in summer because it helps reduce moisture swings and keeps the soil temperature more stable. If you use a Garden Grid™, here’s more on how to mulch with Garden Grids™.

If watering consistency is the hardest part of your summer garden routine, a more repeatable setup can help. Our Garden Grid™ watering systems, GIM™ Automatic Hose Timers, and Garden Grid™ Manifolds are designed to make watering more even, organized, and consistent for better garden growth and peace of mind.

When Should You Add Calcium?

For active blossom end rot, consistent watering is usually the better first place to focus. If adjusting your watering habits doesn't fix the issue for new blossoms after 1-2 weeks, adding a calcium amendment to your soil is the next step for a fast fix. With a good watering routine and calcium added to your soil (if needed), you should see results in new blossoms after 1-2 weeks. 

What About Eggshells For Calcium?

Eggshells contain calcium, and gardeners have used them for years as a simple way to return calcium-rich organic material to the garden.

That said, eggshells break down slowly in soil. So while they can be part of a longer-term soil-building habit, they are not a quick fix for tomatoes that already have blossom end rot.

Some gardeners mix crushed eggshells with vinegar before adding them to the garden because vinegar can help break down the calcium carbonate in eggshells. If you do this, think of it as a soil amendment habit — not an instant cure.

The Simple Takeaway

When you see blossom end rot:

• Remove the affected fruit
• Keep the plant
• Water more consistently
• Use mulch to reduce soil moisture swings
• Avoid overcorrecting with too much water or fertilizer
• Think of eggshells as a long-term soil habit, not a fast cure

The first affected tomatoes won't recover, but that does not mean the whole plant is ruined. Once watering becomes more consistent and the plant settles in, new fruit is often healthy.

Related Garden In Minutes® Resources

• How to Help Your Garden Beat the Heat
• Mulch Above or Below the Garden Grid™?
• 5 Raised Garden Bed Mistakes You Need to Avoid
• Shop All Garden Watering Products