How do you stop blossom end rot?

Keep soil moisture consistent, which is what lets the plant deliver calcium to the fruit. Water deeply and regularly so the soil never dries out completely or stays waterlogged, and apply 2 to 3 inches of mulch to buffer moisture and temperature. Avoid heavy nitrogen feeding, which pushes fast growth that outpaces calcium supply. In containers, water more often since they dry quickly. Steady water and mulch fix the great majority of cases, because the calcium is usually already in the soil.

Do calcium sprays fix blossom end rot?

Usually not, because the problem is rarely a lack of calcium in the soil — it is the plant's inability to move calcium to the fruit under inconsistent watering. Foliar calcium sprays are poorly absorbed and do not reach the developing fruit effectively, so they mostly disappoint. University extension services generally advise correcting watering rather than relying on sprays. If a soil test genuinely shows low calcium or low pH, amending the soil helps, but for the typical case steady moisture is the real cure.

Is blossom end rot a disease? Will it spread?

No, blossom end rot is not a disease and it is not contagious — it is a physiological disorder caused by calcium not reaching the fruit. It will not spread from plant to plant or fruit to fruit the way a fungus or virus does. Affected fruit will not recover, but new fruit set after you correct the watering will be fine. Remove the affected tomatoes so the plant puts energy into healthy ones, and fix the moisture consistency going forward.

What Causes Blossom End Rot on Tomatoes?

Q: What causes blossom end rot on tomatoes?

Blossom end rot is caused by a calcium deficiency in the developing fruit, but it is almost always a delivery problem rather than a shortage of calcium in the soil. Calcium moves through the plant with water, so when soil moisture swings between soaked and bone dry, the plant cannot carry enough calcium to the fast-growing bottom of the fruit, and that tissue breaks down into the sunken leathery brown patch. Inconsistent watering is the primary trigger; most soils already contain plenty of calcium.

Q: Why do only some tomatoes get blossom end rot?

It often hits the earliest fruit of the season and fruit during heat or drought spells, because those are the moments when growth is fastest and moisture is most erratic. First fruits form when plants are growing rapidly and root systems are still establishing, so calcium delivery lags. Certain crops beyond tomatoes — peppers, squash and melons — get it too, and paste and large-fruited tomato varieties are more susceptible. As the season steadies and watering becomes consistent, later fruit typically comes through clean.

Written & researched by Elena Marsh Gardening & Landscaping Editor

Updated October 2026

Three-quarter view of a person harvesting ripe tomatoes into a basket in a backyard vegetable garden, in bright midday sun

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Blossom end rot is a calcium delivery failure, not usually a calcium shortage in the soil. Calcium moves through the plant with water, so when soil moisture swings between soaked and bone dry, the plant cannot carry enough calcium to the fast-growing bottom of the fruit — and that tissue collapses into the sunken, leathery brown patch. Inconsistent watering is the primary trigger; most garden soils already hold plenty of calcium. That single fact reframes the fix: the answer is steady moisture, not more calcium, which is why the sprays people reach for so often disappoint.

Why calcium can't reach the fruit

Calcium is carried in the plant's water stream and does not move around freely once deposited. The bottom of a rapidly swelling tomato is the tissue farthest from the roots and the fastest-growing, so it is the first to go short when the water supply is erratic. A plant that dries out, then gets a heavy soak, then dries again, simply cannot keep calcium flowing steadily to that spot — and the cells there break down. This is why the disorder is fundamentally about watering consistency rather than soil chemistry.

Contributing factor	Role
Inconsistent watering	Primary cause — disrupts calcium transport
Fast growth / early fruit	Outpaces calcium delivery
Excess nitrogen	Pushes growth faster than supply
Low soil calcium or low pH	Occasional true cause; confirm by soil test
Containers drying out	Common in pots that dry fast

Three-quarter view of a person harvesting ripe tomatoes into a basket in a backyard vegetable garden, in warm late-afternoon light

How do you stop it?

Fix the moisture and you fix the disorder in most cases. Water deeply and regularly so the soil never fully dries or stays waterlogged, and lay down 2 to 3 inches of mulch to buffer both moisture and temperature — the same steady-watering routine detailed in how often to water a vegetable garden. Go easy on high-nitrogen feeding, which drives growth faster than calcium can follow. In containers, water more often since pots dry quickly. Because the calcium is usually already present, this consistency is what actually delivers it to the fruit.

Low-angle view of a person harvesting ripe tomatoes into a basket in a backyard vegetable garden, in bright midday sun

Why calcium sprays usually don't work

Foliar calcium sprays are the popular quick fix and mostly a letdown. The problem is rarely a soil shortage, and calcium sprayed on leaves is poorly absorbed and does not travel to the developing fruit effectively — so it does not address the real cause. University extension services generally advise correcting watering over relying on sprays. The exception is a genuine soil issue: if a soil test shows low calcium or low pH, amending the soil is worthwhile. But for the everyday case, steady moisture is the cure and the spray is a distraction.

Low-angle view of a person harvesting ripe tomatoes into a basket in a backyard vegetable garden, in warm late-afternoon light

Why only some fruit is affected

Blossom end rot often strikes the earliest fruit of the season and fruit during heat or drought, because those are precisely when growth is fastest and moisture most erratic — first fruits set while plants grow rapidly and roots are still establishing, so calcium delivery lags. It is not a disease and does not spread from plant to plant; affected fruit will not recover, but new fruit set after you steady the watering comes through clean. Remove the spoiled tomatoes so the plant invests in healthy ones. It also helps to reduce stress overall with proper spacing, and the same inconsistent-water stress behind rot also drives leaf curl.

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