Plant tomatoes for fall harvest in mid- to late-summer in regions where frost does not come until very late autumn or early winter.
Use suckers cut from spring-planted tomatoes to start new plants. A sucker is 4 to 5 inches of new growth usually taken from wherever two stems come together to form a V-shape. New plants also can be grown from a stem cut from the top foot or so of a healthy plant.
How to do it: To root a sucker or cutting remove the lower leaves and set it in a jar of water for an hour or two to start the rooting process. Then plant the cutting in loose compost-rich soil directly in the garden or in gallon nursery pot containing potting mix. Firm the soil around the sucker and water heavily for two or three days. Suckers should grow roots in a week; you may want to start more than one sucker or cutting to hedge against transplant failure.
Not all spring-planted tomato varieties are a good choice for planting in summer. Choose suckers from tomatoes with a short number of days to maturity–about 55 to 70 days,
Two tomato varieties well-suited for summer transplanting and fall harvest are Celebrity which is ready to harvest 72 days after transplanting and Heatwave which is ready for harvest 68 days after transplanting. Other so-called early-season tomatoes are also good choices for summer planting; early-season tomatoes as a group are ready for harvest in less than 70 days from transplanting.
Both Celebrity and Heatwave will tolerate late summer and autumn heat.
It is important to know about when the the first frost will come to your region in autumn or winter. Choose a tomato that can grow to maturity and produce fruit in the number of frost-free days you have left in the season.
More tips: Tomato Ripening Tips For Season End.