How to Plant, Grow, and Care for Oenothera Macrocarpa

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 has 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. They are pollinated by nocturnal insects like hawk moths and sphinx moths. 

They provide 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. They 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. 

What is 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 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.  

Native Area

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 ten 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, survive through cold fall months and winters to come back in the spring. 

Characteristics

Evening primroses are named as such because the flowers only begin to bloom in the late afternoon and remain open until the following morning. The flowers are on the larger side at four inches wide, and each flower blooms for one day. 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. They have multiple short red stems that sprawl across the ground. 

Planting

Planting Oenothera macrocarpa is a rewarding choice for gardeners looking for a hardy, drought-tolerant flowering plant. This perennial prefers a sunny location with well-draining, sandy, or rocky soil.

Begin by loosening the soil where you plan to plant. Make sure it is free from dense clay or excess moisture, as these conditions can lead to root rot. Dig a hole that comfortably accommodates the plant’s root ball. Place it in the hole, and backfill with soil, pressing down gently to eliminate air pockets. Water thoroughly after planting, but once established, Oenothera macrocarpa requires minimal watering and is quite drought-resistant.

How to Grow

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

Light

Missouri evening primrose does best in full-sun garden that receive at least six to eight hours of sunlight per day. Their native habitat is concentrated in areas of USDA growing zones 4-10. These areas experience true four seasons with cold winters and hot summers.

Water

As with most outdoor plants, water early in the morning or late afternoon to avoid losing moisture 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 to help establish your native plants and their flowers, at least twice per week. 

In the second year of growth. It will become more drought-tolerant and can be watered once per week. By the third season of growth, they can be watered once every two 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.

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 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.

Temperature

The most active period of growth occurs during their ideal temperature range, between 70-85°F degrees Fahrenheit. In areas with hot summers, once temperatures are consistently above 85°F in late spring or early summertime, the growth rate will slow down, and showy flowers may drop temporarily. To avoid this, if you live in an area with extreme heat, then growing in light shade – or at least an area with 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.

Fertilizing

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 top dress with compost in the early spring at the beginning of each growing season, but it will continue to grow, flower, and spread regardless. 

Maintenance

Pruning your evening primrose flower is not necessary, but it can be useful in helping contain it. This perennial species can be cut back to a few inches tall just after it blooms in early summer to prevent it 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 six inches before new plant growth appears. During the early summer, deadhead spent blooms to encourage even more showy yellow flowers.  

Propagation

Oenothera macrocarpa 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. Plant out once measurable root growth has formed.  

Common Problems

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

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, plant 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, use traps to control them. 

You may have to deal with birds using the seed as a midday snack. If you’re worried about losing seeds to birds, you can cover your plants with shade cloth or collect the seeds 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