Humidity, especially at night, leads to fungal diseases so it’s also important to know about a plant's fungal disease resistance.
Beans: If you want green beans and shelling beans all summer, try classic Southern beans like Cowpeas, Purple Hull, and in the Deep South, Chinese Red Noodle beans. Yard Long Beans also love heat and humidity. Lima beans/butter beans are usually very reliable in heat, humidity and even during drought.
Tomatoes: Look for tomatoes that come from the Deep South, especially those bred by universities. The large red slicer, Tropic VFN (University of Florida), produces all the way through very hot summers. Ozark Pink VF (University of Arkansas) is highly recommended for very hot climates. These blemish-free, medium-sized tomatoes have a bright taste. For market growers looking for reliability in heat and humidity, Neptune (University of Florida) is an excellent choice. This medium-large red slicer did very well in trials conducted at the University of Georgia.
Eggplant: Take advantage of summer heat by growing an eggplant that loves hot weather. The flavorful French/Italian heirloom 'Listada de Gandia' thrives in hot weather. The better known heirloom variety 'Black Beauty' is also dependable in the South. The long, narrow Asian eggplants like 'Ping Tung Long' produce well throughout intense summer heat.
Peppers: Nematode-resistant bell peppers are the best choices for Southern gardeners. 'Carolina Wonder' and 'Charleston Belle' are both excellent. Hot peppers generally thrive in heat and humidity. Sweet and spicy 'Aji Dulce' peppers have an unusual, complex flavor with a slight hint of heat. They’re not usually bothered by pests and diseases, but they do take a little longer to mature than most peppers.
Cucumbers: Find out which diseases are problematic in your area and use the disease resistance codes found on plant tags to choose which varieties grow best in your area. 'H-19 Little Leaf' from the University of Arkansas has excellent disease resistance and is well adapted to very hot summers. It's good for pickling and also sliced or in salads. 'Ashley' is a slicer particularly recommended where disease is a problem. Another good choice for a heat-loving slicer is the burpless 'Suyo Long'. In addition, it has a sweet flavor. It does need to be grown on a trellis.
Summer Squash and Zucchini: If you have difficulty with summer squash and zucchini in your hot climate, try Moschata summer squash. Moschata types have better pest and disease tolerance and produce well through very hot summers. 'Tromboncino' summer squash also has good blossoms for stuffing. 'Waltham Butternut' winter squash can be harvested small (3-5”) for eating like summer squash. To grow well, Moschata types need nights above 60o F. For something different, you might like to try edible Luffa gourds. When harvested small, they make a nice summer squash alternative.
Winter Squash and Pumpkins: As with summer squash, we recommend choosing Moschata types when growing winter squash and pumpkins in the South. Avoid Pepo and Maxima types. Almost any Moschata will thrive through hot summers; particularly productive varieties are 'Seminole Pumpkin', 'Waltham Butternut', and 'Tan Cheese'. Green-Striped Cushaw is another type of squash altogether. Some Southern gardeners won’t grow anything but Cushaws because they’re very productive and the seeds are very large and tasty. The flesh tastes a little different than most winter squash and is not as sweet, but if sweetened, it can be used in pies.
Melons: 'Top Mark', 'Sweet Passion', and 'Kansas' all have extra disease and pest tolerances. 'Edisto 47' is especially recommended for hot, humid summers where fungal disease is an issue. 'Missouri Gold' produces well during drought conditions.
Watermelon: 'Crimson Sweet' and 'Strawberry' watermelon are good choices where heat and humidity cause fungal diseases.
Okra: The South is the only place in the U.S. where this plant is a reliable grower. Choose older and heirloom varieties that have deeper root systems. Deep roots give the plants resistance to nematodes and improve drought and heat tolerance. These varieties usually take longer to mature. 'Gold Coast' is a variety particularly noted for its deep roots; 'Stewart Zeebest' and 'Beck’s Big Buck' are also excellent heirlooms for the Deep South.
Greens: Lettuce is very difficult to grow when it’s hot and spinach is virtually impossible. But don't give up on summer salads or cooked greens. For cooking, Swiss chard and turnip greens are the best choices in the South. These plants are biennials which means they usually won’t bolt (go to seed) until they’ve gone through their first winter. They stay tender and mild all summer. Sweet potato greens, New Zealand spinach, and young squash leaves and shoot tips can also be used as cooking greens.
Grain amaranths are very productive in high heat and humidity as are many heat-loving herbs such as anise, dill, hyssop, basil and Roselle (Hibiscus sabdariffa). These will add flavor to summer dishes and salads. They also attract butterflies, hummingbirds, and other pollinators to your garden.
I've grown both the green and red varieties of Malabar Spinach and recommend it. The crisp, slightly succulent leaves stay mild in high heat and plants maintain healthy growth all summer. The vines need a trellis or cage to keep them clean. The leaves are good cooked or raw.
(Credits: Southern Exposure Seed Exchange; http://www.veggiegardener.com/5-vegetables-grow-southeast/; https://www.southernliving.com/garden/edible/vegetable-garden-planner; https://www.offthegridnews.com/food/vegetable-gardening-in-the-south/)