Pronounciation: Kall-stro-EE-me-a gran-di-FLOR-a
Sunset Summer annual
USDA Summer annual
Landscape Use: This is a GREAT summer bedding plant for LARGE native gardens, desert restoration, mass floral accent. Not for small spaces!
Form & Character: Low prostrate and spreading, colorful, light and festive, bright cheerfull, carefree.
Growth Habit: Herbaceous warm season annual growing prostrate in a loose and rangy manner to 1.5 to 3 feet in height (depending on density of planting) with a 3 feet spread.
Foliage/Texture: Opposite, pubescent, pinnately compound leaves (5 to 10 leaflets) to 3 inches long and 1 inch wide, distinct green stems between leaf pairs giving it a rangy appearance if observed "up close", occassionally produces small stipular spines that can be an irritant to human flesh; medium fine texture.
Flowers & Fruits: Simple ray flowers, 5 petals, petal yellow orange, 2.5 inches wide, flower petals rarely white, 9 to 10 orange red stamens on distinct anthers and a single stigma. Flowers on short stalks. Fruits dry and spilt open into 8 to 12 sections to disprse seed once plants senesce in fall.
Seasonal Color: Spectacular bountiful orange yellow flowers during August and September.
Temperature: Tolerant of desert summer heat.
Light: Full sun
Soil: Tolerant, though prefers disturbed light soils that are well drained but swaled to collect surface runoff from summer rain.
Watering: In ornamental landscape plantings, this summer annual might need light summer waterings if desert summer monsoon rains are sporadic or light. If the North American monsoon rains in Arizona are heavy, then no supplemental waterings are necessary.
Propagation: Arizona poppy is a prolific seed producer, seeds have a hardened seed coat and will generally not germinate until they are several years old, unless scarified. Seeds can remain viable in desert soils for many years. The low ground habitat created by mass plantings of Arizona calthrop attract birds. To reseed in native landscape plantings shake the seed from dead plants (with their senesced seedpods) in late fall onto the ground and lightly rake into the soil. Otherwise, store seeds in a dry, dark locations until sowing the following late spring to early summer.
Disease and pests: None
Additional comments: Arizona calthrop appears in the desert Southwest during the late summer coincident with the North American monsoon rains. The density of occurence in the desert is a function of the monsoon intensity which is annually variable. During heavy monsoon years such as occurred in 2012, 2013, 2014, and 2021, Arizona calthrop proliferates. During other years when monsoon rains are light (such as 2019 and 2020), Arizona calthrop is rarely seen. Oddly, Arizona calthrop is in the same botanical family as creosote bush. In summary, this is a wonderful and colorful native summer annual for LARGE native gardens. Because of its spreading habit, it is NOT for small garden spaces!