Hardiness zones refer to the average lowest temperature for a geographic area. Traditionally zone 1 is the coldest and zone 11 is the warmest. Plants have a threshold for cold and will not grow much outside that threshold zone. A popular gardening magazine has taken it one step further and added in factors for rainfall and high temperatures, expanding the zones. Zone 13 is frost free, has high summer temperatures and little rainfall. Without supplemental water vegetables will not grow in zone 13. However, with irrigation or hand watering many vegetables will grow.
Winter and spring are the coolest seasons in zone 13. Cool season crops that do well are spinach, peas, chard, kale and leaf lettuces. Plant seeds in October for harvest December through March.
Broccoli can be grown but it takes up a lot of space. Fresh broccoli from the garden doesn't taste a lot different than grocery store broccoli. However growing it at home means you control the insecticides and fertilizer used.
Cabbage, cauliflower and Brussels sprouts have a long maturity period. A warm spell will cause these vegetables to bolt. Bolting means the plant is going to flower and then set seed. Most veggies become bitter and/or woody when they bolt. In Zone 13 it often warms up considerably in February and March for a week or two. Even though the temperature may cool off again, that warm spell nudges vegetables to flower.
Warm Season Vegetables
The warm season planting time is mid-March to mid-April. Temperatures reach the 90s in late April. A few days with 90 degree weather is fine. However vegetables that fruit will face blossom drop if the temperature remains above 95 degrees. Fruiting vegetables include: tomatoes, sweet peppers, hot peppers, eggplant and squashes. Most will stop producing fruit from June through late July. The monsoon season in late summer has cooler temperatures and higher humidity which refreshes the plants and they may start producing again.
Bush beans grow well through all but the hottest times. Pole beans don't do as well since the leaves at the top are farther away from the cooler moister ground.
Corn in a Class by Itself
Corn takes up a lot of space in the home garden. Each plant should have 3 square feet and will product only two, or at the most three, ears of corn. Corn needs to be planted in large blocks for successful production. It's a challenge to grow in zone 13 because by the time the tassels--the male flowers at the top of the stalk--are ready to pollinate the silks--the female flowers--on the cobs, it's too hot. The pollen dries up and won't stick by the time it falls on the silks.