Tomato blossom end rot is a dry, sunken brown or black patch on the blossom end of a tomato, opposite the stem. It is a physiological disorder, not an infectious disease, and usually results when developing fruit does not receive enough calcium consistently; uneven soil moisture is a common reason that calcium delivery is disrupted.
What blossom end rot looks like
The first sign is often a small, water-soaked-looking spot at the blossom end. It can enlarge and turn brown, dark, leathery, or sunken as the fruit grows. The affected area may become firm and dry, though secondary fungi or bacteria can invade damaged tissue and make it soft or moldy. The problem may appear on green fruit before it ripens, and it can affect one fruit while nearby tomatoes look normal.
The blossom end is the end opposite the stem attachment; it is not necessarily the point where a flower was visibly attached. The mark may be shallow or cover a substantial part of the fruit. Affected tomatoes may still ripen, but the damaged tissue will not heal or turn back into healthy flesh.
Why it happens
Calcium is needed to build and stabilize plant cell walls. When cells in the fast-growing end of a fruit do not receive enough calcium while they are developing, tissue can break down. This does not automatically mean the soil contains too little calcium. Calcium may be present but unavailable to roots, or the plant may not move enough of it into the fruit at the right time.
Plants take up calcium with water, then move it through the plant in the flow of water. Fruit receives relatively little water compared with leaves, so shifts in water supply can affect calcium reaching young fruit. A dry spell followed by heavy watering, inconsistent irrigation, or roots damaged during cultivation can interfere with steady uptake. Rapid fruit growth can also raise demand at a time when supply to the fruit is limited.
Other conditions can contribute. Very acidic soil, excessive salts, root injury, waterlogged soil, and an imbalance of nutrients may make calcium uptake or transport less reliable. High nitrogen inputs can encourage vigorous leafy growth, which can compete with fruit for resources. Usually, blossom end rot reflects a combination of conditions rather than a single simple cause.
How to distinguish it from other fruit damage
Blossom end rot usually starts at the blossom end and forms a dry, sunken lesion. That pattern helps distinguish it from several problems that can also leave dark marks or cracks. Check where the damage begins and how it changes over time:
- Sunscald: Pale, whitish, or tan patches develop on fruit exposed to strong direct sun, often on the side rather than only at the blossom end.
- Cracking: Splits radiate from the stem or circle the shoulder, commonly after a change in water availability. Cracking is not the same as a sunken blossom-end lesion.
- Infectious rot: A wet, spreading, foul-smelling, or fuzzy area may indicate decay organisms have invaded the fruit. A blossom-end lesion can become secondarily infected, so appearance can change.
- Physical injury: Bruises, punctures, and abrasions may occur anywhere fruit is handled or rubbed against supports.
These clues are useful, not a guarantee. If a lesion spreads unusually, looks unlike the typical dry patch, or affects leaves and stems as well as fruit, consider asking a local gardening or plant-diagnostic service to identify the problem.
What to do with affected plants and fruit
Remove badly damaged fruit so the plant can direct resources toward healthy growth. A mildly affected tomato may be usable if the damaged area is cut away and the remaining flesh is sound, but discard fruit that is moldy, slimy, foul-smelling, or extensively decayed. Do not eat questionable portions. For food-safety questions, follow guidance from an official food-safety authority; visual inspection cannot make spoiled food safe.
Keep watering as evenly as practical rather than trying to compensate for a dry period with a sudden flood. Check the soil near the roots: it should not swing repeatedly between very dry and saturated. Mulch can help moderate moisture changes, and careful watering at the soil surface can reduce evaporation. Avoid disturbing roots while cultivating or removing weeds near established plants.
New fruit may develop normally once growing conditions become more stable, though existing lesions will remain. Continue to inspect developing tomatoes. The disorder is often more noticeable on early fruit or during challenging growing conditions, but its timing varies with the plant, soil, and weather.
Prevention through steady growing conditions
The most useful prevention is consistent root-zone moisture. Water deeply enough to moisten the active root area, then adjust frequency to the soil, weather, container size, and plant growth. Sandy soil generally dries faster than heavier soil, while containers can dry quickly in warm or windy conditions. There is no single watering schedule that fits every garden.
- Use mulch to slow moisture loss and reduce sharp changes in soil moisture.
- Make sure containers have drainage and do not leave roots sitting in water.
- Protect roots by avoiding deep digging close to tomato stems.
- Use fertilizer according to the soil and plant’s needs; excessive feeding is not a cure.
- Choose a growing location and support system that reduce stress and allow healthy root development.
Tomatoes need moisture, but permanently saturated soil is not the goal. Waterlogged conditions limit oxygen around roots and can impair root function. Aim for a steady balance rather than alternating between drought and saturation.
Calcium amendments and soil testing
Adding calcium is helpful only when low available calcium or unsuitable soil conditions are actually part of the problem. A soil test can indicate soil pH and nutrient status and help determine whether an amendment is warranted. Local extension or soil-testing services can explain how to collect a sample and interpret results for the garden’s soil.
Gardeners sometimes add lime, gypsum, or crushed eggshells after seeing blossom end rot. These materials are not interchangeable. Lime raises soil pH as well as supplying calcium, while gypsum supplies calcium without the same liming effect. Which, if either, is suitable depends on the soil. Eggshells break down slowly and should not be expected to correct a problem in fruit that is already developing.
Spraying calcium on leaves or fruit is not a dependable fix for a plant’s calcium-transport problem. Calcium moves poorly from treated leaves into fruit, and a spray cannot repair a lesion that has already formed. Follow product labels and local guidance if using any garden input; adding more fertilizer without identifying a need can worsen nutrient imbalances.
Does blossom end rot spread?
No: blossom end rot itself does not spread from one tomato plant to another like a contagious disease. It is a disorder arising from growing conditions and calcium supply within the plant. However, damaged tissue can be colonized by decay organisms, and those organisms may cause additional spoilage. Remove fruit with extensive decay and avoid leaving rotting produce in contact with healthy fruit.
If several plants show the same symptom, look for a shared cause such as uneven watering, a common soil condition, or a recent change in cultivation. If only a few fruits are affected, the issue may reflect the conditions those particular fruits experienced while developing. It is not a reason to assume that the seed or plant is infected.
Frequently Asked Questions
Can I eat a tomato with blossom end rot?
A tomato with a small, dry affected area may be usable if the damaged part is removed and the rest is firm and sound. Discard fruit that is moldy, slimy, foul-smelling, or extensively decayed, and follow official food-safety guidance when in doubt.
Should I add calcium right away?
Not automatically. Blossom end rot can occur even when soil contains calcium, because water movement, root health, or other soil conditions limit delivery to fruit. Check growing conditions first, and use a soil test to guide any amendment.
Will watering fix tomatoes that already have brown spots?
No. Consistent watering may help prevent trouble in fruit that is still developing, but damaged tissue does not recover. Remove severely affected fruit and keep moisture more even going forward.
Can blossom end rot affect green tomatoes?
Yes. It often becomes visible while fruit is still green. The lesion may enlarge as the tomato develops, so inspect fruit before it ripens as well as afterward.
Is blossom end rot caused by a fungus?
No. The primary disorder is physiological and involves inadequate calcium reaching fruit tissue. Fungi or bacteria can sometimes invade the damaged area afterward, creating additional decay.
The practical takeaway
Blossom end rot is a sign that a developing tomato’s tissues did not receive calcium reliably; it is not proof that the soil simply needs more calcium. Identify the characteristic blossom-end lesion, remove fruit that is badly damaged or spoiled, and focus on steady moisture, healthy roots, sensible feeding, and soil conditions suited to the crop. Test soil before adding amendments, because the right response depends on what is actually limiting the plant.