When summer temperatures soar, many plants that were enthusiastic bloomers in spring begin to wither under the onslaught of the summer sun. Many plants touted as “heat tolerant” in other parts of the country last about as long as an ice cube on the summer asphalt here in Texas.
Daytime high temperatures are only part of the problem. Elevated summer nighttime temperatures are also stressful to plants because they affect a plant’s physiological and metabolic processes.
CHALLENGES OF SUN AND SHADE
The blast furnace of the summer sun bearing down on a plant creates serious challenges. Not only is the air temperature hot, but direct sun heats up plant tissues faster than the plant can dissipate it through transpiration. Plants may not be able to take up water fast enough to keep up with water loss through the leaves, causing the foliage to wilt during the day but recover at night.
Even at air temperatures in the upper 80s to low 90s, the metabolic processes of some plants can be affected. This results in a reduction bloom production, fruit set, plant growth and related functions as the mercury climbs higher and higher.
Shade provides a break from the blazing sun, but you can’t simply move a plant that needs lots of light into the shade without a reduction in blooming. It takes sun to make carbohydrates, and it takes carbohydrates to fuel growth, vigor and bloom production.
Shady locations often lack color and can tend to go unnoticed as a result. Likewise, dark colors in the shade can go unnoticed. When choosing plants for shade, look for blooms and foliage that are lighter in color to stand out better. White is a color too and has the effect of turning on the lights in a shady spot.
Plants with light foliage colors can be massed to create a more dramatic effect. Use white plants to line a walkway, where they produce the effect of runway lights to direct the eye around a planting bed or down a pathway.
Despite all these challenges of heat, sun and shade, we have many great plant options that take the heat and still flower or provide foliage color through the summer months. Here are a few (well, actually more than 30) of my favorites for the Texas-summer honor roll.
FLOWERS FOR SUNNY AREAS
Angelonia, aka “summer snapdragon” (Angelonia angustifolia), is a great performer available in a range of colors. The upright bloom spikes hold up well in rain, wind and heat.
Zinnias, bred to be compact bedding plants, also work well but may require some deadheading to remove spent blooms.
Purslane and portulaca (moss rose) have succulent leaves and stems, making them both heat- and drought-tolerant. A wide variety of colors and flower forms are available. They work well in hanging baskets, so if you forget to water, they don’t turn to toast.
Celosia, both the plumed (C. argentea var. plumosa) and the cockscomb (C. argentea var. cristata) types hold color well. In addition to the red or yellow plumes, some types have dark-burgundy foliage, too. Its cousin, gomphrena, aka globe amaranth, is likewise at home in the summer sun. It makes a great dried or cut flower, especially if you choose long-stemmed cultivars like ‘Strawberry Fields’.
Lantana (L. camara) is a common perennial in Texas. You can now choose cultivars that are quite compact, ranging from about a foot high and wide to four or more feet in size. Trailing lantana (L. montevidensis) is a low sprawling groundcover-type plant with either light-purple or white blooms.
Salvias are one of the best genera for dependable summer performance in Texas. Among the dozens of great options are S. farinacea (mealy blue sage), S. greggii (Gregg’s sage), S. guaranitica (anise-scented sage), S. ‘Mystic Spires’ and the numerous cultivars within the various species.
The dark-green leaves of Madagascar periwinkle, aka “annual vinca” (Catharanthus roseus), serve as background to blooms in shades of red, pink, lavender and white. Trailing forms are also available that spill over the sides of a container or raised planter. Look for the Cora and Nirvana series, which resist a disease that can destroy older cultivars.
Yellow bells, aka esperanza (Tecoma stans), bear striking masses of golden-yellow, trumpet-shaped flowers from spring to frost. My favorite cultivar is ‘Gold Star’, which has very large bloom clusters and begins flowering when only two-to-three feet tall. However, not everything sold under that name is truly ‘Gold Star’. Another great cultivar is ‘Bells of Fire’ with smaller, fiery red-orange blooms.
Tropical hibiscus (Hibiscus rosa-sinensis) is gorgeous with shiny leaves and dazzling blooms in numerous colors and shades. It can turn your backyard landscape into a Caribbean resort. Despite this flashy diva’s stunning appeal, it isn’t cold hardy and requires you to turn a garage into its Air B&B.
Giant rose mallow (Hibiscus moscheutos) fits well in Texas, where everything is bigger. Dinnerplate-size blooms in red, white, pink and white-with-red last one day but are followed by a long progression to take their place.
Texas Superstar hybrid hibiscus selections ‘Flare’, ‘Lord Baltimore’ and ‘Moy Grande’ are a great place to start. ‘Moy Grande’ bears the largest hibiscus flowers on the planet, reaching up to 12 inches across.
Texas Star hibiscus (Hibiscus coccineus) has five strappy petals and an upright, open growth habit. It comes in red- or white-flowered types.
Red bird of paradise, aka pride of Barbados (Caesalpinia pulcherrima), is my favorite blooming plant of summer. It provides a tropical flair that is especially nice near a pool or outdoor patio. Mulching the base well can extend its range northward a little beyond the state. But be patient: it is slower than a teenager on a Saturday morning to wake up and resume growth in spring. Large, bright red-orange bloom spikes top the plant, commanding attention from anyone passing by as well as from swallowtail butterflies. In my opinion, it is one of the few plants gaudy enough to make people not notice a yard full of plastic pink flamingos.
Thryallis (Galphimia glauca) blooms from summer through fall with a profusion of spikes filled with attractive yellow blooms on four-to-five-foot plants. It has no significant pest or disease problems and is also not favored by deer. Mulching the base well can extend its zone northward. Size and density can be managed with periodic shearing, which results in more new shoots and blooms.
Cape plumbago (Plumbago auriculata) produces clusters of light blue or white blooms all summer long. It prefers a part-day sun location or very bright shade for optimal blooming. Children love the fact that the individual blossoms pull loose with a sticky base that can be pressed against the earlobe for accessorizing with instant botanical bling.
Egyptian star flower, or starcluster (Pentas lanceolata), screams for attention in a part-sun to bright-shade location. The clusters of blooms are butterfly magnets and come in a range of colors, including red, white, pink and purple/lavender.
FLOWERS FOR SHADY AREAS
Impatiens have long been a go-to plant for color in shade, providing a wide color palate of choices in light hues that stand out in dark areas. Wishbone flower (Torenia), named for the small white wishbone seen when an individual bloom is viewed up close, does well in part-sun to bright shade. Choose lighter shades for more visibility in lower-light areas.
Nicotiana, aka flowering tobacco, is another outstanding option for landscape beds with bright-shade to part-sun exposure. A handful of species is common in the garden market, but the more compact N. alata and its hybrids are the choice for landscape color in bright-shade to part-sun beds. The most common colors are variations of white, red and pink.
Shrimp plant (Justicia brandegeeana) is a perennial to Zone 8. Its four-to-five-inch arching salmon-red to rusty-brown showy flower bracts resemble a curved shrimp atop the plant’s stems, earning this plant its unique name.
A separate genus and species known as golden shrimp plant, aka lollipop plant (Pachystachys lutea), has deeper-green foliage and gorgeous bright golden-yellow bracts with protruding white flowers. It is not hardy in most of the state but well worth planting for annual color in shady spots.
The plump, bright-pink bloom stalks of Brazilian plume, aka jacobinia (Justicia carnea), rise to about four-to-five feet high and show off well against the plant’s dark-green foliage. This plant can tolerate deeper shade than many other shade-tolerant plants.
Turk’s cap (Malvaviscus arboreus var. drummondii) is native from Mexico through Texas as well as along the Gulf Coast states eastward to Florida. Blooming from late spring to fall, it produces unique turban-like, bright-red blooms that never unfurl but still are a hummingbird favorite. There is also a white-flowered form and a pink one ‘Pam Puryear’ (aka ‘Pam’s Pink’), while the red blooms of ‘Big Mama’ are much larger than typical.
COLORFUL FOLIAGE FOR SUN
When summer heat limits our blooming options, we turn to foliage to color up the landscape. In sunny areas, copper plant (Acalypha wilkesiana) creates a striking statement with copper/bronze foliage and a tall, upright form.
Joseph’s coat (Alternanthera spp.) comes in shorter bedding-plant forms that bring bold colors of purple, pink, green and creamy-white. It masses well for color in summer landscape beds.
Caricature plant (Graptophyllum pictum) gives a similar effect with foliage in shades of deep green to chocolate, with a center section that is creamy-white with a pink blush.
Canna foliage can be quite colorful, whether the deep-burgundy leaves of ‘Australia’ or the deep-bronze-to-chocolate foliage of ‘Tropicanna Black’. Consider, too, the green-and-yellow striped ‘Pretoria’ (aka ‘Bengal Tiger’) and the multicolored ‘Tropicana,’ which glows with hues of red, orange, coral and green, especially with sunlight backlighting its foliage.
Coleus isn’t just for shade anymore. Many new cultivars are available that can take direct sun, and they can greatly expand your plant palate for summer color. We now have a broad palate of sun-tolerant caladiums too. It used to be just the strap-leaf types that could stand the sun, but now there are sun-tolerant heart-leaf forms as well.
Variegated tapioca (Manihot esculenta ‘Variegata’) is an ornamental version of the cassava plant used to make tapioca pudding and the chewy spheres in boba tea. It reaches around five feet high, with striking green-and-white foliage and red-leaf petioles. Use it to add a tropical look to the landscape.
Purple heart (Tradescantia pallida), the Rodney Dangerfield of colorful foliage plants, “just can’t get no respect.” Equally at home around a rundown shack or the mansion on a hill, purple heart ranges from deep purple in full sun to purple/green in shade and works well in a landscape bed or spilling over the sides of a large container. Resistant to mowing, total neglect, Roundup and probably dynamite, it is definitely one Texas-tough hombre.
COLORFUL FOLIAGE FOR SHADE
Shady spots can tend to be unnoticed, as the lack of light means plants are out of the spotlight. Select foliage to lighten up the area.
Coleus is a staple for bright-shade areas. Caladiums have long served in the same role. Remember, white and light colors stand out best in the shade.
Variegated ginger (Alpinia zerumbet ‘Variegata’) can really draw the attention to shady spots and works well in a bed or a large container near an entryway or on a shady patio.
The white foliage with small green stripes of Aztec grass works great to line a bed, form a mass of white or lead the eye down a shady landscape pathway.
Persian shield (Strobilanthes dyerianus) bears beautiful foliage that appears more silver-looking in the shade and more purple-looking in brighter light. Its leaves look almost metallic in the way they reflect light.
In areas with bright shade, the light chartreuse of ‘Marguerite’ ornamental sweet-potato vine, used as a ground-cover, can break up the dark sea of green between turf, groundcovers or shrubs. The light green/white/pink foliage of ‘Tricolor’ also works well in bright shade.
With so many well-adapted flower and foliage options, there’s no reason for shady areas to be unnoticed or forgotten parts of the landscape.
By Robert ”Skip” Richter, M.S.
Host GardenLine and Garden Success