Every tomato plant ends the season with a batch of green fruit that isn't going to ripen in time. Fried green tomatoes are the well-known use for them, but pickling is faster, needs no oil or breading, and stores for weeks instead of needing to be eaten the same day.
Green tomatoes are firmer than ripe ones and hold up well to slicing thin. Pack the slices tightly into a jar with the garlic, spices, and dill.
Heat the vinegar, water, salt, and sugar until dissolved and pour hot over the tomatoes. Because green tomato flesh is denser than cucumber or zucchini, it takes longer to pick up the brine's flavor - plan on at least 24 hours before tasting, and up to 3 days for a fully pickled flavor throughout.
They'll keep refrigerated for about 3 weeks, longer than most quick pickles on this list because green tomatoes have less water content to dilute the brine over time. More on why some pickles last longer than others is in how long quick pickles last.
Fully green, hard tomatoes work best - avoid ones that have started to blush pink or soften, since those are partway to ripe and will turn mushy in brine rather than staying firm. If frost is coming and there's a mix of green and blushing fruit on the vine, sort them: blushing tomatoes can finish ripening indoors on a windowsill, while the fully green ones are the better pickling candidates.
Pickled green tomatoes have a firmer bite and a sharper tang than a ripe tomato, closer to a pickle than a fresh slice, which makes them better suited to sandwiches and relishes than to dishes built around a ripe tomato's sweetness. Chop them into a relish for grilled meat, or layer slices onto a sandwich in place of a fresh tomato slice for more acidity and crunch.
For the ripe tomatoes coming off the same plant earlier in the season, a tomato basil pasta or mixed tomatoes with basil oil are faster ways to use the bulk of a harvest fresh, saving the pickling method for the stragglers at the end of the season.
See the full quick-pickle guide for garden surplus for cucumbers, zucchini, peppers, and onions using the same brine method.