Three reliable ways to finish them indoors
The paper bag method is the simplest: a few tomatoes in a paper bag with a ripe banana or an apple, folded shut, left somewhere warm like a kitchen shelf. The banana releases ethylene, the bag concentrates it, and things move fast — check daily, because this method can go from green to overripe in a couple of days.
For a larger harvest, lay the tomatoes in a single layer in a shallow box or tray, not touching, ideally on a sheet of newspaper, and keep them somewhere warm and out of direct sun. A spare room, a hallway shelf, the top of a cupboard. Sunny windowsills are the classic mistake: direct sun heats the skin faster than the flesh and you get tough, patchy fruit. Warmth, not light, is what you are after. Check every few days and remove anything soft.
If frost is coming and the plant is still loaded, pull up the whole thing and hang it upside down in a shed, garage or porch that stays above freezing. The fruit carries on ripening from what the stems still hold, and it happens slowly, which is often exactly what you want if you do not fancy twenty ripe tomatoes on the same Tuesday.
The ones that will never ripen are a different ingredient
Treat hard green tomatoes as their own vegetable rather than a failure. They are firm, tart and hold their shape under heat, which makes them genuinely useful. Green tomato chutney is the classic for a reason — chopped green tomatoes, onions, apple, sultanas, brown sugar, vinegar and warm spices, simmered down until thick and glossy, then jarred and left to mellow for a few weeks before Christmas cheeseboards.
