Plants and people are alike when it comes to sizzling temperatures.
Some wilt. Some rejoice in the summer sun.
The right plants in the right place can make gardens burst with summer color, said University of Missouri Extension horticulture specialist David Trinklein. The wrong plant disappoints and is a waste of money.
Missouri's harsh summers can be tricky for gardeners. Trinklein showed annual flowers recently at the annual MU Turf Grass and Ornamental Field Day.
Each year, varieties of ornamental annuals relatively new to the horticulture industry are grown at trial plots at the MU Turfgrass Research Center. They receive the care typical of a home garden and are rated on performance throughout the season.
Large stores may sell plants that aren't suited for this area's extreme temperatures, Trinklein noted, so there's no guarantee a plant that looks pretty in the store will look pretty for long in your garden. For example, Osteospermum, a cheerful daisy-like flower, is billed for full sun. In Missouri, however, it disappoints most gardeners when temperatures rise.
Trinklein suggests growers choose plants based upon the American Horticultural Society's heat zone map (ahs.org/gardening-resources/gardening-maps/heat-zone-map), which is the high-temperature equivalent of the USDA's plant hardiness zone map. An increasing number of garden plants are coded for heat tolerance, which can help buyers determine if a particular plant is suited for their location.
A flower's ancestry gives clues to how well it adapts to Missouri. Some species were brought to the United States from northern Europe, where it is much cooler. Geraniums, often sold as full-sun plants, were brought in by French and English immigrants. While they perform well in a full-sun setting farther north, in Missouri they are, at best, part sun, part shade plants.
A number of ornamental plants do very well in the heat and humidity of a Missouri summer, Trinklein said. Vinca is among the hardiest and most heat-tolerant plants commonly available. It now comes in a wide array of colors, including a cultivar that is nearly black.
Zinnias, native to Mexico, are heat-loving, easy to grow and splashy. Mandevilla, a heat-tolerant vine native to Brazil, loves Missouri heat. So does Brazil's showy bougainvillea, a drought-tolerant vine that reblooms with its bright clusters of showy bracts.
Lantana, native to South America and Africa, is a landscape and pot favorite for prolific blooming. It is drought-tolerant but doesn't like to be too wet.
Angelonia gains popularity as a compact plant with salvia-like spires. Sometimes called summer snapdragon, it adds bright color to hot, sunny spots and comes in a variety of colors.
The ever-versatile petunia now tolerates Missouri heat well too. Once considered a strictly cool weather plant, new varieties such as Proven Winners' Supertunia Vista series tolerate cool and hot conditions equally well. Calibrachoa, which resembles a miniature petunia, tolerates heat well but in Missouri performs best in containers of soilless growing medium.
Marigolds and cannas are reliable standbys for Missouri beds and borders. Many new varieties of dwarf cannas are available to complement taller varieties.
Trinklein encourages gardeners to try new varieties from local greenhouses. Most chain stores carry tried-and-true bestsellers. Local greenhouses may offer new varieties worth a look.