12 Annual Flowers that Can Take the Heat

May 11th, 2021

   Pennsylvania keeps getting hotter and hotter in summer, with 90-degree days more common than ever.

Vinca is one of the heat-toughest annual flowers. This is Tattoo Raspberry.

   Climate forecasters say this is no fluke, that the Harrisburg area is on the road to a climate more akin to Arkansas than past norms.

   If that’s the case, it makes sense when picking our annual flowers each spring to lean toward choices best equipped to handle increased heat.

   One good measure is picking annuals that bloom non-stop right through the triple-digit summers of Dallas.

   Dallas Arboretum conducts trials each year and gives “FlameProof” honors to the heat-toughest flowers.

   If a flower is FlameProof in Dallas, it should have no problem in Dauphin, Dillsburg, or Dallastown, Pa., right?

   Following are a dozen of the best heat-tough annuals you’ll find in local garden centers. Most also aren’t deer or rabbit favorites.

1.) Vinca

   These foot-tall annuals with the glossy leaves can take the worst heat and drought you can throw at an annual. They come in nickel- to quarter-sized flowers of white, pink, rose, red, lavender and pale blue and do best in full sun.

   Good varieties: ‘Jaio,’ ‘Heat Wave,’ and the Titan, Cora, Pacifica, Soiree, Tattoo, and Valiant series.

Both blue and red salvia are heat-tough.

2.) Salvia

   Both the blue-blooming and red/purple types thrive in heat. The spiky, butterfly-attracting flowers grow on 12- to 15-inch stems. Full sun to light shade.

   Good varieties: ‘Signum,’ ‘Rhea’ and ‘Victoria’ (blue), ‘Red Hot Sally,’ ‘Salsa’ and ‘Sizzler’ (red).

3.) Zinnia

   The dwarf types are best at holding off mildew as well as tolerating heat.  Most are hot colors (orange, red, gold), but a few come in pink or white. 15-18 inches tall, full sun.

   Good varieties: ‘Zowie Yellow Flame,’ and the ‘Profusion,’ Zahara, Holi, Preciosa, and Zesty series.

4.) Lantana

Lucky Red lantana

   An arching, perennial sub-shrub in the South, lantana grows as a trailing annual in Pennsylvania. It’ll bloom all summer and even survive a frost or two on the back end. 15-18 inches tall, 2- to 3-foot spread. Blooms red, gold, orange, lavender, ideally in full sun.

   Good varieties: Lucky, Bandana, Bloomify, Luscious, Bandolera, and Landmark series.

5.) Angelonia

   These spiky 15- to 18-inch annuals with the orchid-like flowers might look dainty, but they’re surprisingly heat- and drought-tough. They bloom in purple, pink, blue-purple, and white. Full sun to light shade.

   Good varieties: The Angel Wing, Angelface, Archangel, Serena, Serenita, AngelMist, Carita, Aria, and Alonia series.

6.) Celosia

Celosia Kelos Fire Scarlet Improved

   This plant produces fat, upright flower spikes, usually in red, pink, or gold, on 15- to 18-inch-tall plants. Full sun.

   Good varieties: ‘New Look,’ ‘Asian Garden,’ and the Fresh Look, First Flame, and Kelos series.

7.) Begonia

   The bigger, semi-arching types are even better than the common, short, wax-begonia types. These grow 18 to 24 inches tall and wide, do nicely in containers as well as in the ground, and grow in sun or shade (although with less flower power in shade). Colors are red, pink, orange, or white.

   Good varieties: Dragon Wing, BabyWing, Whopper, Megawatt, and BIG series.

8.) Coleus

   Varieties that have come along in the last 10 years are so much more heat- and sun-tolerant than older varieties of this shade-preferring species. Grown for their colorful leaves, coleus primarily comes in warm shades of burgundy, lime, rust, and magenta. 15 to 28 inches tall.

   Good varieties: ‘Kong Rose,’ ‘Fishnet Stockings,’ ‘Wasabi,’ ‘Dragon Heart,’ and the ColorBlaze, FlameThrower, Main Street, and Under the Sea series.

Euphorbia Diamond Frost

9.) Euphorbia

   These poinsettia relatives grow into 15- to 20-inch balls that are covered with dainty, white or pale-pink, babys-breath-like flowers. They look like big summer snowballs. Sun or light shade.

   Good varieties: The Diamond and Stardust series.

10.) Gomphrena

   Also known as globe amaranth, these heat-lovers with the buttony flowers of red, pink, or purple grow about 18 to 24 inches tall and make excellent cut and dried flowers. Full sun to light shade.

   Good varieties: ‘Strawberry Fields,’ ‘Fireworks,’ ‘Gnome Purple,’ ‘Truffula Pink,’ and the QIS and Li’l Forest series.

11.) Scaevola

Scaevola or “fan flower” in bloom.

   This Australian native with the trailing habit produces small, fan-like blooms that range from lavender to blue to white. Scaevola is especially nice cascading from a hanging basket. Full sun to part shade.

   Good varieties: The Bombay, Surdiva, Scampi, and Whirlwind series.

12.) Alternanthera

   Woefully under-known and under-used, this species with the burgundy or variegated leaves is a durable summer foliage plant that makes an excellent bed edger in its shorter varieties and a showy centerpiece in its upright varieties. Sun or part shade.

   Good varieties: Little Ruby, ‘Red Threads,’ ‘Choco Chili,’ Plum Dandy, and ‘Purple Prince’ (shorties), ‘Party Time’ and ‘Purple Knight’ (upright).