Hartweg's Sundrops

Calylophus hartwegii

Family: Onagraceae (on-uh-GRAY-see-ee) (Info)
Genus: Calylophus (kal-ee-LOW-fus) (Info)
Species: hartwegii (hart-WEG-ee-eye) (Info)
Synonym:Calylophus hartwegii subsp. hartwegii




Water Requirements:

Average Water Needs; Water regularly; do not overwater

Sun Exposure:

Full Sun

Sun to Partial Shade


Unknown - Tell us

Foliage Color:

Unknown - Tell us


12-18 in. (30-45 cm)


15-18 in. (38-45 cm)

18-24 in. (45-60 cm)


USDA Zone 9a: to -6.6 C (20 F)

Where to Grow:

Unknown - Tell us


Unknown - Tell us

Bloom Color:

Bright Yellow

Bloom Characteristics:

Unknown - Tell us

Bloom Size:

Unknown - Tell us

Bloom Time:

Late Spring/Early Summer

Mid Summer

Late Summer/Early Fall

Mid Fall

Other details:

Unknown - Tell us

Soil pH requirements:

Unknown - Tell us

Patent Information:

Unknown - Tell us

Propagation Methods:

Unknown - Tell us

Seed Collecting:

Unknown - Tell us


This plant has been said to grow in the following regions:

Tucson, Arizona

Boise, Idaho

Medicine Lodge, Kansas

Gardeners' Notes:


On Jan 5, 2013, shindagger from Oklahoma City, OK wrote:

I have this plant growing in both full sun and part sun here in Oklahoma. It does equally well in either situation. It will tolerate quite a lot of shade. Naturalizes well, but is not invasive. Its blooms look like a primrose but with slightly smaller flowers and they stay open in the afternoon.


On May 16, 2010, kman_blue from (Zone 6b) wrote:

Hartweg's Sundrops is native to Kansas, Oklahoma, Colorado, Arizona, New Mexico, and Texas and parts of Northern Mexico. It's not endemic to Texas as has been stated. I've seen it growing in the short grass prairies in and around Elkhart, KS growing on sandy soils in well drained short grass prairies. It also grows in the nearby Cimarron National Grassland. I've seen it growing in Barber County near Medicine Lodge, KS also in short grass prairie.

It grows in well drained open prairie mostly and appears to thrive in hot dry situations. I had a couple in my garden in loose well drained soil until they got shaded out by a near-by tree and they slowly died. While they were there, they never needed watering and they bloomed for long periods each summer. If we had an extended dro... read more


On Oct 18, 2007, tucsonjill from Lincoln, NE (Zone 5a) wrote:

For me, this plant is a short-lived perennial; they usually grow for about 3-4 years and then need replacement. But for those years, they can't be beat. They put on a huge show of lemon yellow flowers in the late spring/early summer, a few scattered blooms during the high heat, and another flush in the early to mid fall. They take direct to reflected sun well, and are doing well in a fairly heavy soil. They do need supplemental water in our middle-desert summers.


On Mar 1, 2007, frostweed from Josephine, Arlington, TX (Zone 8a) wrote:

Hartweg's Sundrops Calylophus hartwegii is Endemic to Texas.