Tomatoes Brown On Bottom

If you’ve ever picked a tomato only to find a dark, leathery patch on the bottom, you’ve met blossom end rot. This common garden problem is frustrating, but the good news is it’s preventable. Let’s look at why your tomatoes brown on bottom and what you can do to stop it for good.

Blossom end rot isn’t a disease caused by a bug or a fungus. It’s actually a physiological disorder, a sign that your plant is struggling with internal issues. That brown or black spot starts small and grows, often making the fruit unusable. While it’s most seen on tomatoes, it can also affect peppers, squash, and watermelons.

Seeing that telltale spot can make you think you’ve done something wrong. In reality, it’s usually a simple chain of events inside the plant. The primary culprit is a calcium deficiency in the developing fruit. However, a lack of calcium in the soil is rarely the true cause. More often, the plant can’t move enough calcium to where it needs to go.

Calcium travels with water through the plant. If the water supply is inconsistent—from irregular watering, drought stress, or even excessive rain—the calcium delivery gets interrupted. The blossom end of the fruit, being the furthest point from the roots, gets cut off first. This leads to the cell breakdown we see as rot.

Root Causes of the Problem

To fix the issue, we need to understand what triggers it. Several factors can disrupt that critical calcium uptake.

Inconsistent Watering: This is the #1 cause. Letting soil dry out completely between waterings stresses the plant and halts calcium flow. Sudden heavy watering after a dry spell makes things worse.
Root Damage: Damaged roots can’t absorb water or nutrients well. This can happen from rough transplanting, aggressive hoeing or tilling near the plant, or pests like cutworms.
Soil pH Imbalance: If your soil is too acidic, calcium becomes “locked up” and unavailable to the plant, even if it’s present in the ground.
Excessive Nitrogen: Using too much high-nitrogen fertilizer promotes rapid leafy growth at the expense of the fruit. This fast growth can outpace the plant’s ability to supply calcium.
Cold or Waterlogged Soil: Early in the season, cold soil temperatures can limit root activity and nutrient uptake. Similarly, soggy soil suffocates roots.

How to Prevent Blossom End Rot Step-by-Step

Prevention is your best strategy. Focus on these cultural practices from the moment you plant.

1. Master Your Watering Routine

Consistent moisture is non-negotiable. Your goal is soil that feels like a wrung-out sponge—moist but not soggy.

Water deeply and less frequently, encouraging deep root growth.
Provide about 1-2 inches of water per week, including rainfall. Use a rain gauge.
Water early in the day so leaves dry off, preventing other diseases.
In hot, dry spells, you may need to water every other day or even daily.
Mulch is your best friend here. A 2-3 inch layer of straw, shredded leaves, or wood chips keeps soil moisture even and prevents rapid drying.

2. Test and Amend Your Soil

Start with a soil test. It’s the only way to know your pH and nutrient levels for sure.

Ideal pH for tomatoes is between 6.5 and 6.8. If your soil is too acidic (low pH), add garden lime according to test recommendations.
Add calcium during planting. Mix a handful of gypsum (calcium sulfate) or crushed eggshells into the planting hole. Gypsum adds calcium without altering soil pH.
Ensure good drainage. If your soil is heavy clay, amend it with compost to improve texture and prevent waterlogging.

3. Fertilize Wisely

Go easy on the nitrogen. Choose a balanced fertilizer or one formulated for tomatoes, which often has added calcium.

Avoid fast-acting synthetic fertilizers that cause growth spurts.
Incorporate plenty of compost or well-rotted manure before planting. This provides slow-release nutrients and improves soil structure.
If you suspect a deficiency, a foliar spray of calcium chloride (like Blossom End Rot Spray) can offer a quick fix. It helps the affected fruit, but the real solution is fixing soil and watering habits.

4. Care for the Roots

Handle seedlings gently during transplanting to avoid shocking the roots. Plant them deep—tomatoes can develop roots all along their stems, which creates a stronger system.

Avoid cultivating or digging close to the plants once they are established. You can easily tear the shallow feeder roots that are vital for uptake.

What to Do If You See Rot

If blossom end rot appears, don’t panic. You can save the rest of your crop.

Remove Affected Fruit: Pick off any fruit with spots. They won’t recover and removing them lets the plant focus its energy on new, healthy fruit.
Check Your Watering: Immediately assess your soil moisture and correct your schedule. The next fruits developing on the plant can still be perfect.
Consider a Quick Calcium Boost: A foliar calcium spray can help protect new fruit that’s already forming while you correct the soil conditions. Follow the product label carefully.
Do a soil pH test as soon as possible to rule out that major factor.

Remember, a plant that sets a lot of fruit at once is more suseptible, as the demand for calcium is highest. Some large-fruited heirloom varieties are also more prone to it than others.

Common Myths About Blossom End Rot

Let’s clear up some misinformation you might hear.

Myth: It’s caused by a bacteria or fungus you can spray. Truth: No fungicide or bactericide will help. It’s an internal plant disorder.
Myth: Adding eggshells to the surface mid-season fixes it. Truth: Eggshells decompose far to slowly to provide immediate calcium. They are best added to the soil well before planting or to your compost pile.
Myth: Once a plant has it, all its fruit will be ruined. Truth: If you correct the underlying issues, the plant can produce plenty of healthy tomatoes later in the season.

FAQ: Your Quick Questions Answered

Q: Can you eat a tomato with blossom end rot?
A: You can cut off the affected portion and eat the rest of the tomato. The rot itself is not toxic, but the damaged area can be an entry point for secondary decay or mold, so inspect it carefully.

Q: Does Epsom salt help with blossom end rot?
A: No. Epsom salt is magnesium sulfate. It can actually worsen the problem by competing with calcium for uptake by the plant. Do not use it for this issue.

Q: Are certain tomato varieties resistant?
A: While no variety is immune, plum and paste tomatoes generally show less incidence. Many cherry tomato varieties also seem less prone, possibly due to their smaller fruit size and faster maturity.

Q: Can overwatering cause tomatoes to brown on the bottom?
A: Yes. Soggy soil damages roots, preventing them from absorbing calcium properly. Consistent moisture, not constant wetness, is the key.

Q: Will adding milk to the soil help?
A> This is an old garden remedy. While milk contains calcium, it’s not an efficient or recommended soil amendment. It can smell bad and may attract pests. Stick with gypsum or lime based on a soil test.

By focusing on consistent watering, proper soil preparation, and careful fertilization, you can virtually eliminate the problem of tomatoes browning on the bottom. It’s all about creating stable, healthy growing conditions for your plants. With these steps, you’ll be on your way to a harvest full of perfect, healthy tomatoes.