Mexican primrose (20701 bytes)

Superior Annual and Herbaceous Perennials

By David Staats and Jim Klett, Department of Horticulture, Colorado State University

If you are in the market for some annual or perennial flowers to spruce up your yard, you'll want to know about species that perform well under Colorado conditions.

This information is yours, thanks to research at the W.D. Holley Plant Environmental Research Center on the Colorado State University campus. There, hundreds of flower species are grown and tested for adaptability to Colorado's conditions. These conditions include high altitude, intense solar radiation, drying winds, large fluctuations between day and night temperatures, need for irrigation throughout the growing season and heavy clay soils.

The following perennials are among the superior performers at CSU's research gardens:

  • Oenothera siskiyou - Compact Mexican primrose. This hardy flower with a highly effective display, peaks from early June to August with one to two-and-one-half inch pink flowers. This primrose has an aggressive spreading habit that's easily controlled; its foliage has a good red color in the fall. The plant grows from one-to-two feet high with a six-to-18-inch width.

  • Veronica spicata `Rosea' - Rose spike speedwell. This plant has at least 50 percent flower coverage from early July to late August, with flower spikes that bloom more than five inches. `Rosea' prefers full sun and likes moderately fertile soil. It has no insect/disease problems. It grows from six-to-18 inches tall with a width that varies from two-to-four feet.

  • Veronica spicata `Sunny border blue' - Sunny border blue spike speedwell. This perennial displays dark purple flower spikes about five inches long. Bloom is from early July to mid-August. The plant, which has no insect/disease problems, features an erect growth habit extending from two-to-four feet tall and one-to-two feet wide. It was selected as 1993 Perennial Plant of the Year.

Annual plants that have done well in CSU trials include:

  • Begonia x tuberhybrida "Fortune Mix" - Fortune begonia mix - With vibrant colors, a good color mix, no insect or disease problems, this is a begonia to consider. It prefers shade and well-drained/moist soil. Fortune mix grows to 10 inches high and 10 inches wide.

  • Celosia cristata "Pink Candle" - Pink candle cockscomb - This annual blooms from July until frost with showy flowers with pink tips that fade to white as it ages. Its uniform growth habit, no insect/disease problems and preference for full sun make it an easy plant to grow. Height reaches 24 inches; width, 7 inches.

  • Pelargonium x hortorum "Americana Cherry Rose" - Americana Cherry Rose Geranium. Here is a uniform and compact plant with showy flowers of large quality and outstanding color. This plant blooms from June until frost, prefers full sun and has no insect or disease problems. It will grow to about 13 inches high and 13 inches wide.

  • Petunia x hybrida - Primetime lavender - This is an annual of excellent color, a good spreader with lots of flowers. It is not as vigorous as some groundcover varieties such as Sarafina or Cascadia, but it has a superior appearance late in the season. With no insect/disease problems, this plant grows to 19 inches high and 26 inches wide.

  • Rudbeckia hirta pulcherrima "Indian Summer" - Indian Summer Blackeyed Susan - This is a short-lived perennial grown as an annual in the trial garden. It has long-lasting, large and showy flowers with a uniform growth habit. This blackeyed Susan has no insect or disease problems, A 1995 All-American Selection, it prefers full sun and reaches a height of 26 inches with a width of 27 inches.

  • Rudbeckia hirta pulcherrima "Toto" - "Toto Blackeyed Susan. This is a very dwarf form of blackeyed Susan. The plant has a compact and uniform growth habit; it is a short-lived perennial grown as an annual in the CSU trial garden. Without insect/disease problems, it blooms showy flowers from July until frost. This blackeyed Susan grows to nine inches tall and nine inches wide.

  • Tagetes erecta "Antigua Orange" - Antigua Orange marigold - Here's a healthy plant with large, showy flowers of good orange color that blooms from June until frost. The plant prefers full sun and grows to 14 inches tall and 17 inches wide.

  • Viola x wittrockiana "Majestic Giants Mix" - Majestic giants pansy mix. This pansy has a good mix of colors and blooms with very large flowers. It prefers full sun to partial shade and cool temperatures. Flowering from spring through fall, this pansy variety has no insect or disease problems. It grows to 10 inches high and 14 inches wide.

Photograph of Mexican primrose courtesy of Judy Sedbrook.

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Date last revised: 01/05/2010