When nights turn cold, waiting for every tomato to redden on the vine can put the whole crop at risk. Before a forecast frost, bring in fruit that has already developed. Tomatoes at the mature-green stage can continue to ripen indoors. Very small, uniformly dark-green and hard fruit, however, is unlikely to develop good flavour.

How to spot a tomato that can ripen after picking

Start with size. A mature-green tomato is close to the expected full size for its variety. Its colour will often become lighter: deep green fades towards pale or whitish green, sometimes with a light star on the blossom end. Any blush of pink, yellow or orange means ripening has already begun.

Do not confuse an unripe tomato with a cultivar that stays green when ripe. For green-when-ripe varieties, use the fruit’s slight softness and the variety description rather than colour alone.

When should you harvest before frost?

Watch your local forecast and pick before frost reaches the plants. Prolonged cold can also reduce quality. Oregon State University Extension notes that fruit left on the plant for several days below 50°F, or 10°C, may begin to develop rots.

Cut or detach tomatoes without bruising them. Remove the stems so they cannot puncture neighbouring fruit. Keep only firm, intact tomatoes without suspicious marks. Split, bruised, diseased or frost-damaged fruit should not go into the ripening batch.

Sort the crop before storage

  • Ripen indoors: nearly full-size, firm fruit that is pale green or beginning to colour, with no damage.
  • Use soon: fruit that already shows colour or is ripe; keep it separate so you can monitor it easily.
  • Discard: soft, cracked, spotted, mouldy or frost-damaged fruit, and fruit from clearly diseased plant tissue.

If tomatoes are dirty, clean them gently and let them dry fully. Trapped moisture encourages mould. Check every tomato often after that: one overlooked rot can spread where fruit touches.

How to ripen green tomatoes indoors

Place tomatoes in a single layer, with space between them, in a clean tray or cardboard box. A room temperature of 65 to 70°F, or roughly 18 to 21°C, is suitable for ripening mature-green fruit. Direct light is not required; temperature and maturity matter more. Avoid a very sunny windowsill, where uneven heat can soften fruit.

A cooler, dry room around 60 to 65°F, or 16 to 18°C, can slow the process and spread out the harvest, provided you inspect the fruit frequently. To speed up a small batch, put it in a paper bag or box with a ripe tomato. Tomatoes naturally release ethylene, which stimulates ripening. Do not use an airtight container.

Check the batch every two or three days. Move fruit that begins to colour to room temperature, and promptly discard anything that becomes unusually soft or develops a watery or mouldy patch.

Methods to avoid

  • Do not use the refrigerator to ripen green tomatoes. Cold slows the process and can harm texture and flavour.
  • Do not rely on light alone. A bright windowsill is unnecessary and may create hot spots.
  • Do not pile a large harvest without separators. Pressure and contact make damage harder to notice.
  • Do not keep damaged fruit “to see what happens”. Decay often advances faster than ripening.

Use or share the surplus

Eat tomatoes as they colour and soften. Firm green fruit can be used in a recipe designed specifically for green tomatoes. For home canning, always follow a tested recipe and never can damaged tomatoes or fruit from dead or frost-killed vines. University of Minnesota Extension warns that those tomatoes are unsuitable for safe home canning.

If several kilos ripen at once, plan ahead instead of letting them spoil. You can browse produce available locally or explore the French guide to sharing a garden surplus. For next season, Seeed’s French article on growing tomatoes and courgettes together complements this end-of-harvest guide.

Sources

Photo: “Green Tomatoes” by TigerisLagoona, licensed under CC BY-SA 3.0. Resized by Wikimedia Commons, with no other changes.