The forecast says frost, the plants are still loaded, and not one tomato has turned red. It happens every October, usually within a day or two of deciding that the season has gone rather well. The reassuring news is that most green tomatoes will ripen perfectly well indoors, with nothing more than a tray and a little patience, provided you pick them at the right stage and treat them sensibly. There is no secret to it: sort the fruit, keep it cool and dry, look it over daily, and let time do the rest. What follows is a practical method for UK growers — judging which fruits are worth ripening, sorting and storing them, and speeding things along with a banana, a paper bag or a dark cupboard.
Which green tomatoes will actually ripen
A tomato carries on ripening after it leaves the vine, but only if it reached a certain stage first. Size is the best clue. If a green tomato is roughly full-sized for its variety, firm with the faintest give at the base, and its skin has shifted from deep green to something paler — sometimes with a hint of yellow, cream or pink near the blossom end — it will usually ripen indoors. These are what growers call mature green tomatoes, and they are the only ones worth the space on your trays.
Small, hard, dark green fruits are a different matter altogether. They were still expanding when the cold shut them down, and no amount of warmth, banana or brown paper will turn them red. They will simply soften, wrinkle and eventually rot. That is not a failure; it just means they belong in the chutney pan rather than on the windowsill. Sorting your crop honestly on day one saves a great deal of disappointment later.
How to judge a mature green tomato
- Size: full-sized or close to it for the variety. A 'Marmande' the size of a golf ball is not ready; a cherry tomato the size of a marble probably is.
- Colour: a paler, duller green than the unripe fruit higher up the truss, often with a lighter, slightly translucent look near the blossom end.
- Feel: heavy for its size and very slightly yielding when you press the base with your thumb — not rock-hard, not soft.
- Skin: glossy and taut, with no cracks, bruises, brown patches or soft spots. Damaged fruit rots before it ripens and can spread mould to everything around it.
- Stalk end: the scar should look clean and dry, not weeping or discoloured.
Variety matters too. Smaller tomatoes, especially cherries, reach the mature green stage quickly and ripen indoors reliably; large beefsteaks need a long season and often sulk. If you grow several varieties, ripen them in separate labelled trays so you can see what worked for you next year.
Picking and preparing the fruit
Pick before the frost, not after. A single light frost will not always ruin a tomato, but frozen tissue turns watery and starts to rot within days, so treat the forecast as a deadline rather than a warning. If you have a few days' notice, harvest in dry conditions in the afternoon, when the plants are not wet with dew.
Leave a short stalk — about a centimetre — attached to each fruit, as this helps seal the scar. Do not wash the tomatoes; moisture on the skin invites mould. Instead, wipe off soil and grit with a dry cloth and set the fruit aside somewhere airy for an hour or two to dry completely. Sort as you go into three piles: ripe enough to eat now, mature green and worth ripening, and too small or damaged to bother with.
If a tomato has a brown patch, a split or a soft spot, it will not heal indoors. Use it in the kitchen today or compost it — one rotting fruit can take a whole tray with it.
Ripening them on trays
The simplest method is also the best. Find a cardboard box, a wooden tray or a baking sheet lined with newspaper, and lay the tomatoes in a single layer with a little space between them so air can move and any rot stays isolated. Do not stack them. Keep the tray in a cool, dark, well-ventilated spot: a garage, a shed that does not freeze, a spare room, or a cupboard that stays around 18–21°C.
Check the tray every day or two. Remove any fruit that has gone soft, mouldy or bad-smelling, and move anything just starting to colour to a warmer spot or straight to the kitchen. Ripening happens unevenly, so a tray harvested in one afternoon will give you tomatoes over four to six weeks rather than all at once. Some growers turn the fruit gently every few days, which helps prevent a flat spot where it sits, though it is not essential.
Speeding things up with a banana
Tomatoes are climacteric, meaning they continue to produce ethylene, the gas that drives ripening — and they respond to it from other sources too. A ripe banana, a ripe apple or a single already-red tomato in the same bag or box will noticeably hasten the process.
Put a handful of mature green tomatoes in a paper bag with one ripe banana, fold the top over loosely and leave it on the kitchen worktop. Check daily. Fruit that would take three weeks on an open tray may colour in seven to ten days. The same trick works in a box or a plastic tub with the lid left slightly ajar.
A word of caution: the more you seal the container, the more moisture builds up, and the more likely you are to lose fruit to mould. Paper bags breathe; airtight bags encourage rot. If you see condensation on the inside of a bag, open it up and let the fruit dry out.
The slow method: wrapping for later
If you have dozens of tomatoes and no intention of using them all this month, take the opposite approach and slow everything down. Wrap each mature green tomato individually in a sheet of newspaper, twist the ends, and lay them in a single layer in a box in a cool, dark place at around 10–12°C. Check the box once a week, unwrapping anything that feels suspicious.
Stored this way, green tomatoes will colour gradually over six to twelve weeks, which means you can have your own tomatoes at Christmas. It is an old allotment trick and it still works, provided the fruit was dry and unblemished when it went in and the store stays frost-free.
Lifting the whole plant
If frost catches you short and there is no time to pick, pull up the whole plant, shake off the loose soil and hang it upside down in a shed, garage or greenhouse. The remaining fruit will continue to ripen on the vine for several weeks, drawing on what is left in the stems. Hang a sheet or newspaper underneath to catch falling fruit, and pick as needed. It is untidy, but it is fast, and the tomatoes often taste better than tray-ripened ones.
When things go wrong
- Grey furry mould or black spots: usually botrytis, encouraged by damp and poor air movement. Remove affected fruit immediately, discard the wrapping and improve ventilation.
- Fruit that shrivels instead of colouring: it was not mature green when picked. Use it in cooking.
- Soft, sour-smelling tomatoes: gone too far. Compost them.
- Condensation in bags or boxes: too warm and too enclosed. Open up and cool down.
- Fruit flies: a sign something is already rotting. Clear out the tray and start again with clean paper.
What to do with the ones that never ripen
The small, hard green tomatoes you set aside are not waste. They are the base of some of the best autumn cooking: green tomato chutney with onions, raisins and vinegar; a sharp green tomato ketchup; thick slices fried in cornmeal; or chopped into a salsa with chilli, coriander and lime. They also pickle well and freeze acceptably if you blanch them first. One decent chutney recipe will absorb several kilos and keep for years.
How long will it take?
- Mature green, in a warm room with ethylene: 5–10 days.
- Mature green, on an open tray at 18–21°C: 2–4 weeks.
- Wrapped and stored at 10–12°C: 6–12 weeks.
- On the vine, whole plant hung up: 3–6 weeks, tapering off.
Whichever route you choose, the principles are the same: pick before the frost, keep only sound fruit, keep it dry, and keep an eye on it. Do that, and a glut of green tomatoes in October becomes a supply of ripe ones well into winter — a far better outcome than watching them blacken on the vine.
