David Robson: Some plants like it hot

David Robson

As long as the day temperatures are mild and night temperatures are in the 50s and 60s, gardeners enjoy spending time digging, weeding and watering.

When temperatures climb into the 80s, 90s and higher, gardeners wilt as fast as the plants. Some plants, though, enjoy the high temperatures.

You don’t need exotic plants such as bananas, elephant ears or the new “tall spiky things” that go in containers, such as the many colors and shapes of cordyline, flax or dracaenas, to adapt to heat and humidity. Many vegetables and flowers like warm days and nights, too.

Let’s start with the two big vegetable groups: tomatoes and vining crops.

Red and juicy

Tomatoes thrive in warm weather — up to a point. Plants will continue to grow even when the temperature is in the triple digits as long as the plant has enough moisture and isn’t plagued by the diseases and insects that descend on the plants like a pack of wolves chasing a lost lamb.

However, flowers will abort with 90-plus degree days and nights in the 70s. If the plant is lucky to set fruit, high temperatures will slow ripening to a crawl. In fact, you sometimes can ripen the fruit faster on the kitchen counter than on vines, though vine-ripened tomatoes are tastier than counter-ripe.

The same conditions apply to peppers and eggplants.

On the vine

The vining crops, such as watermelon, cantaloupe and honeydew melons as well as all the squashes, hate cold temperatures. That’s one reason we wait until the end of May to plant them.

Cold temperatures can bleach leaves of the cucurbits, causing them to turn white, which is rather interesting in the garden. But white leaves lead to sunburned leaves, and there is no sunscreen for plants.

Squashes and melons need plenty of moisture to take off and keep producing. But give them a loose, sandy soil and lots of water, and you’ll have melons and squashes coming out your ears.

Green and lima beans like warmth. Peas don’t. But sweet corn grows as high as an elephant’s eye with warm sunny days. In fact, plants develop a better root system with bracer roots if just a little moisture stressed. The water issue comes into play when the stalks are tasseling and silking.

Critters and crawlers

Of course, there is another little factor that comes into play: pollinating insects.

While many plants don’t need any help from nature, there are several plants that require something flying or crawling around to move pollen from point A to point B. Without these six-legged creatures, nothing happens.

Most of us think about honeybees, though native wasps and hornets can also pollinate. Plants aren’t that picky. They just need the pollen transferred from the anthers to the stigma. Which means even you can act as the bee.

Wake up early and arm yourself with a cotton swab such as a Q-tip or a fine make-up or artist paint brush. Rub the inside of one flower, then move to another flower and rub with the same swab. Keep doing this flower after flower. You don’t need to wear a yellow and black striped shirt.

Some like it hot

For flowers, just about all the annuals like warm conditions — provided, as stated above, there is sufficient moisture.

Marigolds like it warm. Zinnias seem to develop more flower buds when it’s hot. Petunias grow by leaps and bounds with temperatures in the 80s and above. Geraniums like warm days but prefer cool nights.

Scaevola, angelonia and all the newer plants on the market native to Australia or South Africa have built systems to process temperature and humidity and turn them into flowers. In fact, many of them can tolerate more of the drier conditions without quickly wilting.

Outdoor herbs

Many perennial herbs do well with hot, humid and even dry conditions. Annual herbs, such as basil, do not.

Rosemary, though somewhat finicky with winter temperatures, develops a thicker epidermis and more of a whitish coating on the leaves, called “bloom,” which can be terribly annoying when talking about the other bloom, which helps keep moisture in.

Sage, thyme, oregano, dill and fennel go to town, provided there aren’t caterpillars eating the leaves of the latter two. Hot, dry conditions concentrate fragrant oils, and if you’re growing the herbs for culinary use, you’ll find them more potent.

David Robson is a specialist with University of Illinois Extension. For more gardening information or for your local extension unit office, go to www.extension.uiuc.edu/mg.