Hi @veginitis
Tomatoes are seasonal vegetables - that is, they germinate, grow, flower and fruit within a 6 month period, usually Spring to Autumn. After they've borne their crop (which contains the seeds for the next growing season), they die down.
If you want to try getting them to grow on over the cooler months, the plants could be pruned back quite severely to encourage new growths from the leaf axils, then lifted and potted up into pots no less than 450mm in diameter, using a quality vegie and herb potting mix. Water in thoroughly with a half strength liquid fertiliser. The pots should be placed in a protected spot where the plants will get plenty of sun but shelter from cold winds. Keep the potting mix moist but not wet and include a liquid fertiliser every four to six weeks.
Transplanting and potting up is worth a try but the plants won't flower if the weather is too cold and cloudy, as Winter usually is in southern areas. They need warm to hot temperatures and plenty of direct sun stimulate the flowering and fruiting process.
