The Gardener Within: Master Gardener and author Joe Lamp'l offers tips on growing heat-loving annual and perennial plants that add a pop of color to the summer landscape.
Like humans, plants have to cope not only with the heat but also with energy-sapping humidity, wind and drought. They grow more slowly, their leaves fade, wind batters them and, in areas of high humidity, they’re prone to insects and disease. High nighttime temperatures don’t let plants recover from heat stress.
The annuals and perennials on my heat-lovers list need very little special care. Start with great, compost rich soil, and then a good weekly soaking and deadheading to remove spent blooms is about all they ask.
Plants like coreopsis, rudbeckia, echinacea and liatris get a little ragged-looking as their blooms fade or they develop seed heads; others stop making new flowers once insects have pollinated the plant. Deadheading redirects energy into making new flowers.
In my book, zinnias are a favorite for taking the heat with the best of them. With a little deadheading or cutting back periodically, they’ll put on an amazing display all summer long.
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Exactly where to snip when deadheading isn’t always clear. The plant’s appearance should be your guide. You could just pinch off coreopsis’ buttons, for example, but that would leave brown stalks sticking up above the foliage. Snip at the base of the flower stem, above a pair of leaves, instead.
There are also several annuals and perennials in the list, like the poppy, spider flower and lantana, that don’t need deadheading. Stake the taller perennials like rudbeckia and liatris to keep them standing tall.
Some hot-weather plants, like perennial butterfly weed, don’t like to be transplanted once they’ve settled into their sites; they’ll allow transplanting from their original containers, but don’t try moving them later.
Some annuals, like California poppy, don’t tolerate transplanting, either. Sow their seeds by placing, not scattering, two or three seeds in holes the recommended distance apart. After they emerge, thin the seedlings, leaving only the healthiest one.
Heat-loving flowers will do even better if they’re mulched. Mulch keeps plant roots cool and lets rain and irrigation water soak slowly into the soil rather than running off. Mulch also slows evaporation. Organic mulch also improves the soil. Scatter 2 to 3 inches over the bed, being careful to avoid burying low-growing plants like golden fleece.
A heat-lovers sampler:
• California poppy. Striking, cup-shaped flowers in scarlet, rose, pink and gold over silvery-green foliage; 12 inches tall; full sun; well-drained soil; reseeding annual; Zones 6-10.
• Butterfly weed. Tiny clusters of intense orange, red or yellow flowers on 18- to 36-inch stalks; full sun to part shade; tolerates humidity; supports monarch butterfly larvae; Zones 3-9.
• Rudbeckia. Season-long, bright yellow daisy-like flowers; 2-3 feet tall; full sun; tolerates humidity; great for cut flowers, striking planted in drifts; Zones 3-7.
• Spider flower. Rose, white, pink and violet crowns of flowers; 4 feet tall; full sun to part shade; tolerates humidity; rampant self-seeder can take over the garden; prickles along the stems; annual; Zones 2-11.
• Gayfeather. Shaggy purple spikes bloom from the top down; full sun; well-drained soil; tolerates humidity but not wet, soggy winters; 18-24 inches tall, great vertical accent; Zones 3-8.
• Coreopsis “Jethro Tull.” Compact 2-inch golden-yellow flowers with tube-shape petals; 12-18 inches tall; full sun; well-drained soil; tolerates humidity, resists mildew; Zones 5-9.
• Purple coneflower. Drooping purple petals surround large, spiny “hedgehog” center cones; 3-4 feet tall; full sun to part shade; well-drained soil; tolerates poor soil and humidity; divide clumps every 3-4 years; will self-seed if not deadheaded; Zones 3-8.
• Golden fleece. Tiny, half-inch, yellow daisy-like flowers and aromatic, finely divided foliage; 6 inches tall; full sun; well-drained to sandy soil; excellent, spreading ground cover, rock garden plant or front of border filler; grown as an annual, Zones 9-10.
Joe Lamp’l, host of “Growing a Greener World” on PBS, is a Master Gardener and author. For more information visit www.joegardener.com. If you’re not sure what plants may be invasive in your area, check with your local garden or horticultural center.