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Selections for 2020


Oklahoma Proven is a plant promotion program coordinated by faculty in the Department of Horticulture and Landscape Architecture at Oklahoma State University. The goal of the program is to recommend plants well-adapted for use across Oklahoma.


Tree for 2020


Carpinus species

The genus Carpinus includes the native C. caroliniana, American hornbeam and C. betulus, the common or European hornbeam, both common in the trade.

American hornbeam is a slow-growing, understory tree with an attractive globular form. It typically grows 20-35' tall. The European hornbeam grows in full sun to part shade and needs little pruning when grown as a tree, but responds well to hard pruning if grown as a hedge; it is a medium-sized, tree that grows 40-60’ tall with a pyramidal to oval-rounded crown.

Both trees produce flowers as separate male and female catkins, with the female catkins giving way to distinctive clusters of winged nutlets. Leaves are dark green and can produce respectable shades of yellow, orange and red in fall. Trunks have smooth gray bark and distinctive muscle-like fluting. Upright, columnar forms are available.


  • Exposure: Full sun or light shade
  • Soil: Tolerates medium moisture, well-drained soils
  • Hardiness: USDA Zone 3-9 (4-8)




    Shrub for 2020

    Red Yucca

    Hesperaloe parviflora

    Not a yucca, this member of the Century-Plant family (Agavaceae) produces soft, yucca-like, evergreen leaves, 2-3 ft. in length, crowded on the perennial’s short, woody base. The flower stalk rises 5 ft. and bears showy, coral-colored, tubular flowers on arching, wand-like, pink stems. Leaves are plum-colored in winter; blue-green other times.

    Red Yucca is drought-resistant, and adaptable to a variety of soils. Deer may browse the foliage, while the flowers attract hummingbirds. Hesperaloe parviflora 'Perpa‘, Brakelights® Red Yucca has vibrant, brake light-red blooms which are a great color improvement to this species! Yellow flowering forms are also available. Use in mass plantings for a dramatic effect in xeriscape and waterwise gardens. Good container specimen.

    • Exposure: Full sun
    • Soil: Dry soils, excellent drainage
    • Hardiness: USDA Zones 5-10




    Perennial for 2020

    Golden Variegated Sweet Flag

    Acorus gramineus ‘Ogon’

    Acorus gramineus is commonly called grassy-leaved sweet flag. It is native to wetland areas of China, Japan, Korea, India, Thailand, Myanmar and the Philippines. 'Ogon' is a dwarf plant which features iris-like tufts of narrow, grass-like, variegated leaf blades (6-12" tall and 1/4" wide) which are striped with yellow and green but primarily appear as yellow.

    Sweet flag is easily grown in average, medium to wet soils in full sun to part shade and perform well in both boggy conditions and consistently moist garden soils. Never allow soils to dry out. Plants appreciate some relief from hot summer sun (e.g., afternoon shade or filtered sun) when grown in hot summer climates. Foliage is sweetly fragrant when bruised (hence the common name of sweet flag).

    • Exposure: Full sun, part shade
    • Soil: medium to wet
    • Hardiness: USDA Zones 5-9
    2020 Acorus gramineus ‘Ogon’




    Annual for 2020

    Brazilian Verbena (improved cultivars)

    Verbena bonariensis

    Commonly called Brazilian vervain, this plant is a rapid-growing, clump-forming tender perennial. Plants typically form a 1-foot tall basal clump of dark green leaves from which rise erect, slender, wiry, branching, stems to 3.5’ tall bearing clusters (to 2” across) of tiny rose-violet flowers.

    Though a tender perennial it often grows as an annual in Oklahoma. If sited in sheltered locations with southern exposures, plants can survive mild winters. Even if plants do not survive winter, they often remain in gardens for a number of years through self-seeding. Plants have no serious insect or disease problems, though watch for powdery mildew. This species is very heat and drought resistant and makes a great cut-flower and attracts butterflies and hummingbirds. Improved cultivars include ‘Little One’, ‘Lollipop’, and Meteor Shower®.

    • Exposure: Full sun/part shade
    • Soil: Poor soils, good drainage
    • Hardiness: Use as an annual
    2020 Verbena bonariensis 2020 Verbena bonariensis