Blossom End Rot on Tomatoes: Cause and Fix

By Azura · Updated June 2026 · Raised Garden Hub is reader-supported. When you buy through links on our site, we may earn an affiliate commission at no extra cost to you.

Blossom end rot is the dark, sunken spot on the bottom of a tomato — and it’s a watering problem, not a disease. It happens when the plant can’t move enough calcium to the fruit, almost always because the soil moisture is swinging between wet and dry. The fix is consistent watering, not more calcium.

What blossom end rot looks like

The first sign is a small, pale or water-soaked area on the blossom end — the bottom of the fruit, opposite the stem. Within a few days it turns brown-black, flattens out, and becomes leathery or papery. On larger tomatoes the affected patch can cover a quarter of the fruit.

It appears on the earliest fruits of the season, often when plants are growing fast and setting fruit for the first time. Later fruits on the same plant are frequently fine — especially once your watering becomes more consistent.

Blossom end rot is not a disease. There is nothing to spray, no fungus to kill, and it does not jump from plant to plant.

The real cause: a calcium-uptake problem driven by water

Here is where a lot of gardening advice goes wrong: blossom end rot is not usually caused by calcium-deficient soil. Most raised-bed mixes — and most garden soils — contain more than enough calcium. The problem is delivery.

Calcium moves through a plant in one direction only: upward with water, through the xylem. When moisture is abundant and steady, calcium flows continuously into the developing fruit. When the soil dries out and then gets drenched again, that flow stutters. The fast-growing blossom end of the fruit gets starved first, and the cells there collapse and die.

The inconsistency is the culprit:

• Watering too lightly so the top few inches dry out between sessions
• Missing a watering day during a heat wave
• Heavy rain followed by a dry week
• Planting in containers or raised beds that drain quickly

The fruit most at risk is the one that was growing during the moisture stress — usually the first cluster on the plant. Later clusters, formed after you stabilize your watering, often escape completely.

Raised beds are actually more prone to drying out than in-ground beds because they drain faster and have more exposed surface area. If your raised bed is shallow, there is less soil volume to buffer against dry spells — another reason depth matters.

Why raised beds dry out faster

A 6-inch-deep raised bed can lose most of its available moisture in a day or two during summer heat. A 12-inch bed holds significantly more, which buys you a larger buffer between waterings. The soil mix you use also matters: mixes heavy in perlite or coarse compost drain very freely, which is good for roots but demands more frequent watering. Check moisture 2–3 inches down before every watering session — if it’s still damp at that depth, you can wait.

How to fix blossom end rot mid-season

1. Water deeply and consistently. This is the only real fix. Aim for 1–2 inches of water per week, delivered in fewer, deeper sessions rather than daily light sprinkles. Deep watering encourages roots to go down where moisture is more stable.
2. Mulch immediately. A 2–3 inch layer of straw, wood chips, or shredded leaves slows evaporation dramatically and smooths out the moisture swings that trigger BER. This alone can stop new cases from developing.
3. Remove affected fruit. Cut them off. The plant will redirect energy to healthy developing fruit instead of trying to salvage damaged ones.
4. Back off nitrogen. High nitrogen fertilizers push rapid leafy growth, which competes with fruit for calcium. If you’ve been heavy-handed with a balanced or high-N fertilizer, ease up.
5. Check your soil pH. Calcium availability drops below pH 6.0. Raised beds filled with peat-heavy mixes can drift acidic over time. A soil test and a light application of agricultural lime can help — but only if pH is actually the issue, not as a first guess.

Do eggshells or calcium sprays help?

This is the most common myth around blossom end rot, and the honest answer is: probably not for your current crop.

Eggshells are calcium carbonate, but they break down slowly — often over a year or more — so adding them mid-season delivers almost no plant-available calcium before the season ends. Worked into beds during fall prep, they are a reasonable long-term soil amendment. Sprinkling them around plants in July will not save your tomatoes.

Foliar calcium sprays (calcium chloride or calcium nitrate diluted and sprayed on leaves or fruit) can provide a small, temporary boost. Some growers see modest improvement. But if your soil has adequate calcium — which most do — and watering is still inconsistent, sprays will not fix the underlying problem. Steady irrigation always beats any calcium shortcut.

Will affected fruit be safe to eat?

Yes. Cut off the dark, leathery bottom and eat the rest. The affected tissue is unpleasant in texture but there is no pathogen, no toxin, and no health concern. If a large portion of the fruit is affected, compost it — otherwise, slice it up.

Crops besides tomatoes that get blossom end rot

BER is not exclusive to tomatoes. The same calcium-uptake mechanism affects:

• Peppers — especially bell peppers; the sunken spot appears on the blossom end just like tomatoes. Yellowing pepper leaves and BER often share the same watering stress root cause.
• Zucchini and summer squash — the blossom end of the fruit turns soft and rots; often confused with pollination failure, but the cause is moisture stress.
• Eggplant — less common but occurs under the same conditions.

If you’re growing several of these crops in the same bed, consistent watering helps all of them at once.

Prevention going forward

• Pick the right bed depth — at least 12 inches for tomatoes to give roots room and buffer moisture. See how deep a raised bed should be for guidance.
• Use a quality soil mix — a well-draining but moisture-retentive blend matters. A good raised-bed soil mix and a soil calculator help you fill your bed correctly from the start.
• Choose BER-resistant varieties — paste types like Roma are more susceptible; beefsteak and cherry types are generally more forgiving.
• Avoid planting too early — cold soils restrict root activity and calcium uptake even when watering is good.
• Consider a drip line or soaker hose — the single most effective tool against BER in raised beds. It keeps moisture steady at the root zone without the wet-dry swings that overhead watering creates. A self-watering raised bed does the same job automatically by wicking even moisture up from a reservoir.
• Choose good companion plants — some gardeners pair tomatoes with moisture-conserving companions; see companion plants for tomatoes for what works well in a raised bed.

The bottom line

Blossom end rot looks alarming but it is entirely preventable. The tomatoes you’ve already lost this season are gone, but new fruit set after you stabilize your watering will come out clean. Mulch the bed today, adjust your irrigation schedule, and pull the damaged fruit. That’s the whole fix.

For further reading on keeping tomatoes healthy in a raised bed, see why tomato leaves curl, why tomato plants won’t flower, and the best raised beds for tomatoes.