QUICK ANSWER
Blossom end rot is a dark, leathery, sunken spot on the bottom of the fruit, caused by a calcium shortage inside the tomato — but the actual cause is almost always inconsistent watering, not a lack of calcium in your soil. Fix the watering and new fruit typically stops showing spots within one to two weeks.
Why This Happens
Calcium doesn’t move through a plant on its own — it travels with water, pulled up from the roots as the plant transpires. When soil moisture swings between soaked and dry, that calcium delivery gets interrupted right when the fruit needs it most, during early development. The soil almost always has enough calcium already; the problem is that inconsistent watering stops it from reaching the fruit in time.
This is why blossom end rot tends to show up in bursts — a dry week followed by heavy watering or rain is the classic trigger, especially on the first flush of fruit each season before a plant’s root system and your watering rhythm have both settled in.
One quick way to tell it apart from other problems: true blossom end rot starts at the bottom of the fruit and feels firm, dry, or sunken — not wet, moldy, or spreading from a wound on the side. If it looks or feels different from that, you may be looking at a different problem entirely.
How to Fix It This Week
• Water on a consistent schedule — deep watering once or twice a week beats a little bit every day. Inconsistency is the actual problem, not total volume.
• Mulch around the base of each plant to buffer soil moisture against hot, dry stretches.
• Skip the calcium spray or supplements unless a real soil test shows a genuine deficiency — in most gardens, adding more calcium does nothing because the soil already has plenty.
• Remove affected fruit so the plant isn’t wasting energy on it, and check new fruit as it forms — it should come in clean once watering evens out.
Related Questions
Does adding crushed eggshells fix blossom end rot?
Usually not. Most garden soil already has more than enough calcium; the issue is getting it to the fruit consistently, which eggshells don’t solve.
Can I still eat a tomato with blossom end rot?
Yes — just cut away the affected spot. The rest of the fruit is unaffected and safe to eat.
Will it come back on the same plant?
Not necessarily. Once watering evens out, most plants stop producing affected fruit within a couple of weeks, even on the same vine.
Related: Overwatering signs and fixes · Underwatering signs and fixes · Plant Problems & Troubleshooting guide
