Oenothera Macrocarpa: How To Grow Evening Primrose

Oenothera macrocarpa, also known by its common name Missouri evening primrose, is a low-maintenance herbaceous perennial with stunning yellow flowers and narrow grey-green leaves. 

They make a lovely addition to wild gardens and native plant gardens. Their bright yellow flowers earned them the Royal Horticultural Society Award of Garden Merit. Since they can survive in poor soil, including rocky prairies, clay soil, and limestone glades, they can also add interest to rock gardens with dry soil where other plants may struggle to grow. 

Missouri evening primrose is most easily identified by its bright yellow flowers, which are the size and shape of teacup saucers. Like all members of the evening primrose family, the flowers open in the late afternoon into the following morning. For this reason, they are pollinated primarily by nocturnal insects like hawk moths and sphinx moths. 

Adding them to your native landscape provides a much-needed food source for nighttime pollinators, even when they’re potted plants. Another benefit of Missouri evening primrose is that it flowers over a long period of time. Their bloom time stretches from spring to mid-summer. 

These native flowers open before many others in the spring. When the flowers die back in the late fall, they will form seed pods among their foliage that will readily self-seed and spread over the years. The stems and leaves trail along the ground in a spreading growth habit, making them the perfect ground cover. 

Quick Care Guide

All About Oenothera Macrocarpa

As mentioned above, Missouri evening primrose is well known for its narrow green leaves and showy yellow flowers that bloom profusely throughout the late spring and into mid-summer in rock gardens, clay soil, and limestone glades. The flowers are on the larger side at 4 inches wide, and each flower blooms for one day. 

The genus name involves two root words – oeno, or donkey, and thera, or trap – which refer to its ability to provide a space for donkeys to rest for a moment. It has an alternative botanical name and is also known as Oenothera missouriensis. It has many a common name, with bigfruit evening primrose and Ozark sundrop among them.  

Evening primroses are named as such because the flowers only begin to bloom in the late afternoon and remain open until the following morning. During their bloom time, they emit a mildly fragrant scent that attracts nighttime pollinators such as hawk moths and sphinx moths. The yellow flowers stand in contrast to the beautiful green foliage along multiple short red stems that sprawl across the ground. 

Perennial Missouri evening primrose is native to almost the rest of the United States, in parts of Mexico and Central Southern United States like Texas, Oklahoma, Arkansas, Kansas, Nebraska, Missouri, Illinois, and Colorado. It is especially prolific throughout Missouri, specifically in the Ozarks. It’s there these showy plants grow about 10 inches tall and spread.

The area with the most species of this native plant is the southwest of the United States, and there are species of the Oenothera genus in every state except for Alaska. This perennial Oenothera missouriensis plant can tolerate heat and drought and also survive through cold fall months and winters to come back in the spring. 

Missouri Evening Primrose Care

Missouri evening primrose produces beautiful and showy 4-inch wide pale yellow flowers among its lovely green foliage. When grown in its native habitat, Oenothera missouriensis is low maintenance and drought tolerant. 

Sun and Temperature

Missouri evening primrose does best in full-sun garden or yard areas that receive at least 6-8 hours of sunlight per day. Their native habitat is concentrated in areas of USDA growing zones 4-8. These areas experience true four seasons with cold winters and hot summers. The most active period of growth occurs during their ideal temperature range, between 70-85 degrees Fahrenheit. 

In areas with hot summers, once temperatures are consistently above 85 degrees in late spring or early summertime, the growth rate will slow down, and showy flowers of Oenothera missouriensis may drop temporarily. To avoid this, if you live in an area with extreme heat, then planting Oenothera missouriensis in light shade – or at least an area where there is morning sun and afternoon shade – is the better option to get the most out of your evening primrose even through the heat of the summer. 

This perennial plant species will go dormant, and the leaves will die back in the winter and revive in the spring from self-sown seeds and taproots to grow tall and flower in summer.

Water and Humidity

As with most outdoor plants, water early in the morning or late afternoon to avoid losing moisture to evaporation during the heat of the day. If you forget to water at dusk, wait until the following morning. You’ll need to water regularly during the first season of growth to help establish your native plants and their flowers, at least 2 times per week. 

In the second year of growth. It will become more drought-tolerant and can be watered 1 time per week. By the third season of growth, they can be watered once every 2 weeks. Missouri evening primrose prefers dry soil, so it’s better to underwater than to overwater. 

Be sure to avoid watering the leaves and planting in waterlogged sites, like near a downspout or low-lying area in your garden, especially in the winter with accumulating snowfall. Too much moisture may damage the roots and cause other issues, such as root rot.

Oenothera Macrocarpa Soil

Aside from its drought tolerance, another benefit to adding Missouri evening primrose to your landscape is that it can tolerate poor soil and remain its showy self. This means the planting site does not necessarily need to be amended in any way. Oenothera macrocarpa species thrive in dry clay or rocky soils and are usually found in limestone glades or rocky prairies in their native habitat. This makes them perfectly suited for rock gardens, but they also flower well as potted plants. 

When growing in containers, the type of soil mix is not necessarily as important as providing your Oenothera species of plants with well-draining soil. Adding perlite to a standard potting mix can help increase drainage. As mentioned above, consistent soil moisture can cause issues with these leaves and their mildly fragrant yellow flowers. Their preferred soil ph range is neutral to slightly acidic.

Fertilizing Oenothera Macrocarpa Plants

Missouri primrose is an attractive choice as a perennial flower because it’s very low maintenance. It can survive and flower on very little water, tolerates a wide variety of soil types, and doesn’t require any regular fertilizer or soil amendments. They actually prefer lean soil rather than rich fertile soil. This goes for both the plant and newly germinating seeds.

Although fertilizing isn’t necessary, this plant species can benefit from the boost of a layer of compost at the planting site, although this isn’t a must. You may also topdress with compost at the beginning of each growing season in the early spring, but macrocarpa will continue to grow, flower, and spread regardless. 

Pruning Missouri Evening Primrose

It is not necessary to prune your evening primrose flower, but it can be useful in helping contain it. This perennial species can be cut back to a few inches tall just after they bloom in early summer in order to prevent them from going to seed and further spreading. 

If your goal is to use Missouri primrose as a ground cover over a large area, you may choose to forgo pruning altogether and let it grow wild! To maintain the overall health of your primrose, it’s best to cut back old growth in the early spring to a height of 6 inches tall before new plant growth appears. During the early summer, deadhead spent blooms to encourage even more showy yellow flowers.  

Oenothera Macrocarpa Propagation

An Oenothera macrocarpa plant will voraciously self-seed. If the bright and showy yellow flowers are left standing on the plant after their bloom time at the end of the season, they will die back and form seed pods. The seed pods can be left to spread seeds on their own, or the seed can be collected for more purposeful sowing elsewhere in the garden. 

Cuttings are also an option if you wish to have more Missouri evening primrose even faster. Take a plant cutting just below a leaf node and remove the lower foliage. Place this cutting in a glass of water, and roots will form over the next few weeks. Once measurable root growth has formed, your macrocarpa plants can be planted out.  

Troubleshooting

As mentioned above, Missouri primrose is mostly pest and disease free! There are, however, some things to be on the lookout for. 

Missouri Evening Primrose Growing Problems

Most growing problems stem from a lack of sunlight. If you notice that your evening primrose is not producing yellow blooms and subsequent seeds, it may need more sunlight. To avoid having to dig up and move your primrose, follow planting instructions for your specific location. 

In areas with very hot summers, they can benefit from being planted in light shade. In most other areas, they prefer to be grown in full sun. These native plants do not do well in shaded areas.  

Pests

Another great benefit of adding Missouri primrose plants to your landscape is that they have no serious pest issues and are deer resistant. That being said, slugs and snails can occasionally chomp on the foliage in spring and early summer, but they rarely cause anything other than superficial damage. 

If the damage becomes excessive, they can be treated with slug and snail bait commonly found at big box stores and hardware stores. Follow the directions on the bottle for application. If you’re looking for a more natural alternative, you might want to try beer. Slugs and snails have a known attraction to beer. Fill a container with beer, bury it so that the lip of the container is at soil level, and slugs/snails will fall in and be unable to get back out. 

You may have to deal with birds using the seed as a midday snack. If you’re worried about losing seed to birds, you can cover your plants with shade cloth or collect the seed as they come out of the pods. Then you can sow the seed under cover of sediment to deter birds.

Diseases

Root rot is the main disease that can affect your native Missouri primrose. Root rot is generally caused by saturated soil from over-watering. The symptoms of root rot will appear as a soft mushy stem, wilting, and of course, rotten roots. This type of rot is harder to recover from but can be remedied if there are still fresh, white roots on the plant that have not yet turned to mush. 

If you’re growing in a container, cut back the rotted roots and plant them into a pot of dry soil. When grown in the ground, back off of watering your plant and let the surrounding soil completely dry out before watering again. If your evening primrose was planted in a site that becomes easily waterlogged, you might need to dig it up and transplant it to an area with better drainage, with sandy or clay soil. 

Frequently Asked Questions

Q: Is Oenothera macrocarpa invasive?

A: Missouri evening primrose is not technically considered to be invasive. However, it does spread aggressively and is a prolific perennial self-seeder. 

Q: How do you grow Oenothera macrocarpa?

A: These plants do best in lean clay or sandy soil located in full sun.  

Q: How do you care for Oenothera?

A: Water regularly during its first growing season to help the plant establish itself. During its second growing season, it will become more drought-tolerant. 

Q: Do evening primrose attract bees?

A: The bright yellow flowers attract many pollinators, including bees, but because they tend to bloom in the late afternoon and into the evening, they are pollinated primarily by hawk moths and sphinx moths.  

Q: Does evening primrose come back every year?

A: Yes, evening primrose is a perennial plant in USDA zones 4-8. 

Q: What grows well with evening primrose?

A: Since Missouri evening primroses spread along the ground, they make a great addition to an area of the garden that needs perennial ground cover. In their native habitat, they grow in large clumps in meadows and sandy or rocky prairies. 

Q: Where should I plant evening primrose?

A: They should be planted in a full-sun location. 

Q: Should you cut back evening primrose?

A: If you wish to prevent its aggressive spread, cut back your evening primrose after the blooms are spent but before the seed pods have formed.