Cutting open a tomato and finding small white, green or thread-like structures emerging from the seeds can look alarming. Many people first assume they are worms or contamination. In many cases, however, the explanation is botanical: the seeds have begun to germinate inside the fruit itself.

This phenomenon is called vivipary. It can occur in tomatoes and some other fruits when conditions inside allow a seed to break dormancy before the fruit has fully broken down.

What exactly is vivipary in a tomato?

Mature seeds normally remain dormant for a period. Signals within the fruit help prevent immediate germination. As the tomato becomes very ripe and ages, and depending on temperature and moisture, that balance can change.

The seed then begins the same process it would start in moist soil: it takes up water, activates metabolism and produces a small root or shoot. The unusual part is that all of this happens inside the tomato pulp.

Is it a worm?

Usually not. Vivipary sprouts arise directly from the seeds and often look like pale threads, sometimes developing green parts if growth has progressed. If each structure is visibly attached to a seed, a germinating seed is the likely explanation.

An insect larva does not emerge from the seed in this organised way. If there is independent movement, tunnelling, external damage or other clear pest signs, that is a different issue.

Can you eat a tomato with sprouting seeds?

Vivipary itself does not make the tomato toxic. University horticultural extension sources describe the phenomenon in overripe tomatoes and note that the fruit can remain edible. The practical decision depends on the tomato's overall condition.

If the flesh smells normal and there is no mould, fermentation, slime or major decay, sprouting seeds alone do not require you to discard it. Texture and flavour may be less appealing because the fruit is often very ripe.

When should you discard it?

“Vivipary is harmless” does not mean every tomato showing it is in good condition. The same fruit may also be spoiled. Discard it when you see:

• fermented, rotten or distinctly abnormal odour;
• visible mould in the flesh or around the stem;
• large slimy or watery areas;
• leaking and collapsed structure;
• insect damage or rot unrelated to germination;
• other clear signs that the fruit has broken down.

Why is it common in very ripe tomatoes?

A seed needs moisture and a signal that allows it to leave dormancy. A tomato already provides plenty of moisture. As the fruit ages, the mechanisms keeping the seed dormant can weaken, so a very ripe tomato can become a surprisingly favourable germination environment.

That is why vivipary is more often seen in tomatoes that have remained fully ripe for some time than in freshly harvested firm fruit.

Does refrigeration prevent it?

It is not useful to refrigerate every tomato solely to prevent sprouting while it is still ripening, because temperature also affects flavour and texture. A better strategy is to buy or harvest an amount you can use reasonably soon and monitor ripeness.

Once a tomato is fully ripe and will not be used promptly, refrigeration can slow general deterioration. Letting it warm slightly before serving can improve its sensory quality.

Can you plant the sprouted seeds?

Often, yes. A living sprout can sometimes be transferred carefully to suitable potting mix. There is no guarantee the future plant will produce tomatoes identical to the original fruit, especially with hybrid varieties or cross-pollinated seed.

A seedling that has grown long inside the tomato is also delicate and easy to damage when separated from the pulp.

Does it happen in peppers too?

Similar internal germination can occur in other fruits, including peppers. It is different from the curious phenomenon of finding a small pepper growing inside another pepper; the two have different botanical causes.

How to keep tomatoes from reaching this stage

• Check ripe tomatoes every day or two.
• Use the softest ones first.
• Do not leave fully ripe fruit in a very warm place for many days.
• Use bruised or cracked tomatoes sooner.
• Buy quantities that match your real consumption.

For ripeness and storage, see our guide to choosing and storing tomatoes.

Bottom line

Those strange threads growing from tomato seeds are usually not parasites: they are a plant starting to grow too early. Vivipary is a germination phenomenon, not a tomato disease. If the fruit is otherwise sound it can still be usable; if it also shows rot, mould or fermentation, discard it because of those spoilage signs.

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