Superior Annual and Herbaceous
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
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
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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