USDA Hardiness Zone 6

Plants are known to be cold hardy to at least -10°F.

Other Cold Hardiness categories

Common Name: Jupiter's Beard, Red Valerian

Centranthus ruber is a versatile plant, able to be used almost anywhere in the landscape except full shade. Long blooming except during the heat of the summer. Deadhead after the spring bloom for better appearances. Reseeds some, but not a problem. Quite drought tolerant, it will still do nicely in medium and high water use areas, except for wet, soggy clay. It appreciates good drainage and moderate amending but will do well in poor soil. Centranthus ruber 'Alba' is a pleasant white blooming variety. Readily available at local nurseries.

Common Name: Diana Rose of Sharon, Althea

Rose of Sharon, or Althea, is another reliable old-fashioned garden plant well suited for the Texas Panhandle. My favorite cultivar is Diana because of the brilliant, pure white 4-5” flowers and somewhat glossy green leaves. Diana is also one of the smaller varieties up to about 6 - 8 feet, while others can reach 10’ tall. Similar to most altheas, 'Diana' is a prolific bloomer.

Common Name: Missouri Evening Primrose, Bigfruit evening-primrose, Ozark Sundrops

Oenothera macrocarpa, and O. missouriensis have been used interchangeably. Native over a wide range including the plains and wooded areas, carries the common name, Missouri evening primrose, bigfruit sundrops and Ozark Sundrops. 

Common Name: Butterfly Blue Pincushion Flower

Scabiosa columbaria ‘Butterfly Blue’, though first discovered in Ireland, will thrive very nicely in your transition zone as a border plant along turf, where it’ll receive medium to medium high water. Amend the soil well with organic matter for rich blooms and keep it deadheaded to prolong blooms. Afternoon shade is recommended. A little more trouble than usual, but well worth the softening effect this compact, mounded and cheery plant brings to the border; a Perennial Plant of the Year for 2000.

Common Name: Rock Rose, Rose Mallow Pavonia

Although there is question in my mind whether pavonia is a native in Texas, it’s been naturalized for a long time and is found growing in the Edwards Plateau and south Texas. Pavonia has been cold hardy for me for at least 5 – 6 years. Readily reseeds to the point of being a nuisance, but this is a minor annoyance.

Common Name: Chamisa, Rabbitbrush

Chamisa or rabbitbrush is a medium tall shrub with blue-green stems that produce clusters of golden yellow flowers from September throughout fall, very showy in the landscape. Matted hairs on thin leaves cast a silvery appearance. Native throughout the southwest, in warmer climates it is evergreen. The official name has been changed to Ericamera nauseosa, but is still referred to as Chrysothamnus (meaning golden bush). Seeds prolifically -- is a good pass-along plant to friends, neighbors, relatives and passersby.

Common Name: Arizona Rosewood

Arizona rosewood is one of the few native evergreen trees or tall shrubs that are low water-use. Underused in the Texas Panhandle, mostly due to lack of availability. But with searching in Albuquerque or Santa Fe, one should be able to locate a specimen. Faster growing than the Chisos rosewood. Long slender, serrated, glossy green leaves with white flowers in summer.

Common Name: Cypress Vine

Cypress vine is a native annual tropical vine of the Americas, but has naturalized in Florida and the Gulf Coast areas; said to be cold hardy to Zone 6. Fine lacy or thread-like leaves twine as it grows, putting on scarlet red flowers in summer. In addition to being a climber, it can be used as a groundcover.

Common Name: Sand Lovegrass

Sand lovegrass is a warm season bunch grass typically found in sandy soils east of the Rockies over a wide range of the U.S. The grass clumps themselves are usually 12-18" tall with the plumes rising to 3-4 feet. Will grow in clay and poorer soils. Very pleasing wispy, arching habit with a soft sway and rustle in the wind. Can grow in partial shade. Seed heads are somewhat purple, fine textured. Will reseed. Low or no water-use.

Common Name: Oregon Grape Holly

Oregon grape holly is an evergreen holly-like shrub native to the Pacific Northwest Rockies down into California. Upright, it is slow growing but can reach a height of 8 feet. Best when grown in shade, especially out of afternoon sun. Prefers a more humusy soil but will only required once a month watering when established, however, can also be placed in medium and high water-use areas. Bright yellow flowers in spring, followed by dark blue berries in summer. The thick, glossy, holly-like leaves have spines at the points. Leaves turn from green to red in winter.

Common Name: Crocus

Spring blooming crocus is a favorite among gardeners, heralding the end of winter. Many species of crocus can actually bloom in winter months. I've seen crocus bloom as early as mid Janurary, although February and March are more common. There are many different species of crocus, most people choose them by color, height or bloom period. Their colors range from yellow to purple, lavender, violet and white, some in combination of colors. Commonly, Crocus chrysanthus, C. venus,  and C. angustifolius. C.

Common Name: Snow in Summer

A good drought tolerant ground cover for use in a border, in a xeristrip or a rock garden. Evergreen grayish green leaves with fine hairs (tomentose). Will grow too tall and gangling in too rich and moist a soil. Some areas of the country have noted Cerastium tomentosum to be invasive, but I have not seen those tendencies here. A good substitute for the annual alyssium. Cerastium tomentosum var. columnae is a commonly available variety.

Common Name: Standing cypress.

Reseeding biennial, native to Texas, and the southeastern US. The red tubular flowers make it attractive to hummingbirds. The upright stalks are brittle and break off easily.

Standing cypress will flower the first year, and may, or may not come back a second year, but you should see some seedlings. Transplant those. The glossy green foliage to the right in this picture belongs to Anisacanthus quadrifidus wrightii, flame acanthus.

 

Common Name: Silver Blade Missouri Evening Primrose

Gorgeous! Luscious goblet shaped lemon yellow flowers on this native wildflower that also develops elongated seed capsules. The lighter, silvery sheen of the leaves distinguishes the O. macrocarpa var. incana subspecies, and is also an evening to morning bloomer.

Common Name: Violet Cloud Hybrid Skullcap

A new hybrid skullcap from High Country Gardens. A cross between two native skullcaps, Violet Cloud likes the soil lean and well drained. A sparkling addition for the rock garden, xeristrip and any low water-use area. Additional watering is required during establishment the first year, after that, it should be drought tolerant.

Common Name: Texas Pink Skullcap, Cherry Skullcap

A Plant Select Plant for 2004, Pink Texas Skullcap has often been listed as a Zone 7 plant, but it is reliably cold hardy in Zone 6 and in protected Zone 5b sights. I’ve grown it in my xeristrip since 2000. Long blooming with no maintenance ever performed. These low growing, mounding skullcaps are excellent for Panhandle xeristrips and rock gardens. Native varieties are S. drummondii, and S. resinosa. The hybrid cultivar, S. x ‘Violet Cloud’, introduced by High Country Gardens, is an excellent violet skullcap as well as the natives.

Common Name: Calamint

Calamint, a member of the mint family, sparkles with white/pale lavender flowers in late summer into fall. Solid green foliage emits a pleasing mint fragrance. Attracts bees. Sometimes referred to as lesser calamint. Calamintha nepeta spp nepeta covers itself with light blue flowers.

Common Name: Hyssop, Hummingbird Mint, Licorice Mint

Agastaches are some of the Southwest's showiest natives and one of our native perennials where must breeding and hybridization is being done. Native to slightly higher elevations that 3600 ft., it requires either afternoon shade or medium water-use. It has not been reliable in coming back for me, but it has for others. Well drained soil is a must. Nonetheless, it is easy to be seduced by its masses of blooms and alluring fragrances. Hummingbirds certainly are entranced.

Common Name: Honeysuckle, yellow

Yellow honeysuckle is a much better choice, along with Loncera sempervivens, than the traditional and invasive Japanese honeysuckle usually sold. Fragrant and yellow blooming, a good climber and groundcover. Average garden soils with low and medium water-use. Can be low water-use once established.

Common Name: Switchgrass

Switchgrass is one of the best native ornamental grasses of our tall prairies. Switchgrass forms upright bunches of wide 1/2 inch green blades, with open pale purple inflorescence arising another 2 feet in late summer to fall. Switchgrass will thrive with every other week supplemental irrigation. There are many varieties of switchgrass, 'Prairie Sky' is the most drought tolerant (low, xeric) with blue blades. Other fine selections are 'Heavy Metal' with metallic lavender blue foliage turning reddish towards fall, and 'Shenandoah' with leaf blades tipped in red.

Common Name: Gray Santolina, Lavender Cotton

Lavender cotton, or gray santolina is a low mounding woody subshrub that should live on the lean side. Not that it won't overgrow if fed. It will maintain its compact shape in poorer soils without amending or fertilizing. Small silver gray leaves cover the shrub. Tiny yellow button flowers appear in summer. Evergreen, the santolinas are native to the Mediterranean area. Aromatic and edible, it's leaves were used as a flavoring in broths, sauces and grain dishes. Low water-use.

Common Name: Daffodils, Jonquils, Narcissus

Daffodils are the most notable of the spring bulbs. Reliable from year to year, daffodils can be depended upon to bloom even when faced with late season blizzards and are unpalatable to deer and squirrels. Daffodils aren't too particular about soil, but do better in amended soil, planted about 4 inches deep in November and December. Typical bloom times are February through April, depending on the variety, and there are thousands of varieties to choose from.

Common Name: Sweet Autumn Clematis

Although usually sold as Clemantis paniculata, it could be C. terniflora. Sweetly fragrant, low water-use vigorous growing vine for great late summer display. Creamy white flowers form silvery seed heads.  Cut back in spring as it blooms on new growth.

Common Name: Red pincushion flower

Perennial with lyre shaped leaves, similar in appearance to scabiosa, native to central Europe. In fact, it's synonym is Scabiosa rumelica. Deep purple red pincushion-like flowers. Knautia macedonica may suffer from our alkaline soil if not well amended with compost and well drained. Will reseed some. Has a pleasant wild look. Popular with nectar feeding insects. Deadheading doesn’t seem to be necessary.

Common Name: Cascading Ornamental Oregano, Lebanese Oregano, Hop Oregano

Exciting perennial ornamental oregano for your low water-use or Mediterranean style garden. Spreads slowly by rhizomes and is easily propagated by root cuttings in fall or early spring. The flowers elongate as the summer progresses, eventually drying to a papery brown by summers end. In a wet fall, some new flowers may still appear. O. libanoticum is best placed to drape over a rock to showcase it’s drooping nature.

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