Late Summer Bloomers that can Take the Heat

When July and August heat rises into the upper 90’s day after day only perennials best adapted to the west can bloom, cheering up the gardener and nourishing the pollinators.

Above: Desert Four O’clock, Mirabilis multiflora.

Desert Four O’clock, Mirabilis multiflora, puts on a floral spectacle just before dinner until just after breakfast. Rose-purple trumpets cover a mound of thick oval leaves spreading 3'-4' in diameter, 12"-18" high. The outer stems lay flat on the ground but do not root, performing a self-mulching function. Even in very dry conditions, the fleshy tap root continues to supply water for flowers all summer into fall. Large oval seeds fall from papery packets, often making new plants. It’s an autumn surprise when a hard frost kills the whole mound to the ground and it breaks off like a giant tumbleweed. The next spring it will come back late so don’t be in a hurry to fill the space with anything except spring flowering bulbs. Desert Four O’clock is too wide to mingle with most other perennials, but is a splendid companion for medium to large, drought-tolerant shrubs. In most years in Colorado it needs no water after establishing, however a woodchip or squeegee mulch or once-a-month watering can provide even more flowers.

Dotted Gayfeather, Liatris punctata, (above) hides quietly in the landscape all spring and half the summer. Its rough narrow leaves form a tuft 10"-12" high that might be mistaken for a grass. Then in late summer, spikes of bright purple-pink gay feathery flowers suddenly appear. The spikes can stand 12"-18" high and are a beacon to butterflies and bees into September. This local native inhabits dry shortgrass prairie. Its thick, deep moisture-storing taproot insures a display of color and nectar in the driest years.

Mojave Sage, Salvia pachyphylla, is a very heat-tolerant plant, native to the mountains of southern California, not the Mojave Desert, but a great plant for a xeriscape. It is considered a subshrub, usually growing to 2' x 2', sometimes sprawling, sometimes mounding. It has very silvery green foliage that is aromatic, protecting it from browsing deer and rabbits.

With the summer heat coming on, the violet-blue flowers appear on 4"-8" wands, surrounded by exquisite smoky mauve-purple bracts. This show continues into fall. Mojave Sage is attractive to bees, butterflies and even hummingbirds. It is refreshingly colorful and even sexy in a dry, western garden. Of course it loves sun, but it does tolerate some shade and some water. It does not, however, tolerate regular watering or most drip irrigation. Plant it where the winter sun will hit it, that is, not on the north side of a hill, rock, or building. Salvia pachyphylla, a Plant Select Winner, is a little slow to develop and a little fussy about watering, but well worth a little care.

Above: Chocolate Flower, Berlandiera lyrata. PHOTO: David Winger/PlantSelect Chocolate Flower, Berlandiera lyrata, is also a Plant Select Winner and it does indeed smell like chocolate in the morning. It makes a mounding mass of dark-eyed yellow daisies 12"-20" high and wide. Chocolate Flower has a long bloom time that can be extended by dead-heading in July if the flowers have gone to seed. Do let it go to seed at some point to create a bigger display that will magnetize bees, butterflies, and birds.

This wildflower likes it dry, with occasional deep waterings. Don’t be fooled when the flowers droop, bend over or close up around noon. This may well be a smart strategy to reduce water loss through transpiration. More water may harm or kill this xeric star. It really likes the sun, but is OK with light shade. Encourage self-sowing with a gravel mulch.

Above: Summer blooming Globemallow, Sphaeralcea fendleri. PHOTO: Harlequins Gardens

The Globemallows are natives of the southwestern US into Colorado. These dryland plants have been important food, medicine and dye plants for Native Americans for thousands of years. This spring we had massive displays of orange when 8" tall Cowboy’s Delight, Sphaeralcea coccinea, painted our usually gray roadsides. The Globemallows come in many sizes and colors. I started summer-blooming Sphaeralcea incana or fendleri from seed from Plants of the Southwest and it has thrived in my very dry xeriscape for 25 years. This form is 5'-7' tall with strong, upright stems that are lined with hundreds of 1" mallow-type flowers, mostly orange and some pink. These continue to bloom for weeks and are one of the most popular plants in my summer garden, mobbed by many kinds of bees seeking its rich source of pollen and nectar. It dies to the ground in fall, but you can leave the stems for the birds to eat the seeds in winter and just cut them down in the spring. This form is no longer available from Plants of the Southwest but may be found online and sometimes we have the plants at our nursery.

More common and beautiful at 2'-3' high is Sphaeralcea munroana which is orange-flowered and blooms May into August. Removing the spent flowers can extend bloom time. Munro’s Globemallow is also drought-tolerant and does not do well in wet clay. Amend clay soils with squeegee or expanded shale to provide drainage and oxygen.

So many of us have moved here from wetter climates and think that giving ample water to plants is responsible plant care, but many western plants, like those discussed here are touchy about water. Saturated soil leaves little room for air. Oxygen is just as important to plants as water and especially in the west, plants need the associations with oxygen-loving mycorrhizal fungi. So we can adapt our gardens to what may be an increasingly drier climate by making separate areas that are only watered 5-10 times a year, where the soils have been built for drainage and oxygen, and where we grow western plants that thrive in sun and drier conditions. Someday water conservation might not be optional.

Mikl Brawner and his wife Eve co-own Harlequins Gardens in Boulder, specializing in organic veggie starts and herbs, natives, sustainable roses, xeriscape, unusual perennials, and products to build healthy soil.