When tomatoes are fully matured and ready to be harvested, they will fall right off the vine without much effort at all. Simply give them a little tug and twist and they’ll let go if they’re ready.
If they’re not quite ripe, but you’d still like to harvest (because of impending bad weather, pests, etc.), then you should leave a bit of the stem on the fruit in order to encourage them to finish ripening. The tomatoes on the vine that you see at the store are likely harvested before they’re fully ripe so that they don’t go bad in transit.
When tomatoes are fully matured and ready to be harvested, they will fall right off the vine without much effort at all. Simply give them a little tug and twist and they’ll let go if they’re ready.
If they’re not quite ripe, but you’d still like to harvest (because of impending bad weather, pests, etc.), then you should leave a bit of the stem on the fruit in order to encourage them to finish ripening. The tomatoes on the vine that you see at the store are likely harvested before they’re fully ripe so that they don’t go bad in transit.