Here in the West, we have numerous members of a wonderful group of drought tolerant native flowers, many of which are hard to find, or altogether overlooked. These plants can take partial shade or brutal full sun, require only occasional watering, propagate easily, and bloom profusely in the evenings and early mornings. Several of the species are evergreen, and provide an attractive green ground cover whether they are in bloom or not. Additionally, they provide a source of nourishment to a different subset of nectar feeders than many of the other flowering plants, these are from the family Onagraceae, genus Oenothera, evening primrose. Other names for members of the group include Sundrops and Flor de San Juan.
General characteristics of Oenothera are that they can be annual, biennial, or perennial. Blossoms are white, pink, yellow, have four petals, four sepals, eight stamen and a four-celled seed pod forms against stem. The blossoms tend to be from two to four inches in diameter, and the plants can be from six inches to five feet tall. They range in altitude from sea level to 9,000 feet, but are most common from 1,000 to 7,000 feet. Cold hardiness varies but is usually to about 10?F.
Evening primrose has been used historically for medicinal purposes, and recent clinical studies indicate that the oil of evening primrose is high in Gamma-linolenic Acid (GLA) and is useful in regulating fatty acids, reducing hot flashes and PMS, and improving eczema and psoriasis (when used topically). Other studies concerning use in some types of heart disease look promising, but it's too early to tell.
Did you know that 21 native Oenothera have been documented in Arizona alone? In a good year, you may find three Oenothera species plants available locally. Most likely the Baja (O. stubbii), Mexican (O. berlandieri) and Missouri (O. missouriensis). All are great in full sun, but a little extra late afternoon or morning shade allows longer enjoyment of the blossoms. All three are attractive low water use ground covers. The O. stubbii and O. missouriensis have large yellow flowers. I have killed both Missouri and Baja primrose plants by overwatering. I now put four to five different low water use plants, including a couple of Missouri tubers, in an area served by a half gallon drip.
The Mexican evening primrose (O. berlandieri) is perhaps the best known of the desert southwest Oenothera. This plant is a living contradiction. It is amazingly drought tolerant, surviving on just natural precipitation in some of the local microclimates. In others, minimal watering is enough, yet it produces abundant, very delicate pink blossoms. A little additional water results in a profusion of pink, which can last much of the spring, summer and into the fall. Propagation is easy. I keep a one gallon container and divide it twice a year. Plant two thirds, repot a third. Just add a little water and the plant does the rest. It makes a nice evergreen groundcover and bronzes slightly in the winter. If given more water than it needs to survive, it can become invasive.
My recent enjoyment has been from three native primroses that have voluntarily appeared in the yard. Two were recognizable because they had the classic evening primrose lanceolate leaves. One turned out to be Prairie evening primrose (O. Albicaulis) and the other, which I'm still researching, has beautiful large yellow blossoms on a six inch plant and seems to be perennial. The third has been an amazing experience. When it appeared in the yard, it didn't look like anything I'd ever seen before. It did not have classic primrose lanceolate leaves or gray-green color. For two months it grew taller and put out radial branches. I cut back one side of it as it was blocking the sun of several other plantings. Finally, over Fourth of July weekend, it bloomed just before sunset. What a knockout! At the end of each of 12 or 15 remaining radial branches, two to four lemon-yellow blossoms opened, and at the top of the five foot center spike, four to six bloomed. They were about three inches in diameter and smelled like plumeria, but not as strong. Several hummingbird moths gorged themselves on the nectar, their feeding tubes caked with pollen. There was a repeat performance each evening. The plant turned out to be Hooker's evening primrose (O. hookeri), a biennial. I hope to have seeds to share in early September.
Sources of native primroses are hit or miss. Mexican evening primrose, and occasionally Baja or Missouri, can be found at Ace Garden Place in one gallon pots. Missouri can be ordered, for as little as fifty cents a tuber, from catalogues like Fields and Gurneys and will survive here. (Don't order them in the late summer unless you can handle wintering them over in a cold frame or microclimate which will allow them a fighting chance to establish during our colder months. Mine arrived in November having broken dormancy during shipping. Between that shock and the puppy getting into the make-shift cold frame and trying them as chew toys about half survived.) Plants of the Southwest in Santa Fe, NM has seed available for 5 different evening primrose, not including the Mexican. White Flower Farms had plants of two species (O. fruiticosa glauca 'Solstice' and O. Speciosa 'Rosea') in their spring 1998 catalogue. Shepherds has seeds for one (O.Pallida).