Mexican Evening Primrose: Deceptively Aggressive

Mexican evening primrose is a perennial ground cover that’s blanketed with delicately beautiful pink flowers when in bloom. But be forewarned — it can be deceptively aggressive. Here’s how to grow and care for this native wildflower — if you dare!

Mexican evening primrose (Oenothera speciosa) is a dainty-looking wildflower that wouldn’t look out of place in a cottage garden. But in fact, it’s a tough perennial that’s native to the US Central Plains and parts of the Chihuahuan and Sonoran Deserts.

Plants have small, bright green leaves and bell-shaped flowers that are a particularly pretty shade of pink. Mexican evening primrose may look delicate, but this is a resilient plant that easily handles the desert’s sun and temperature extremes.

Their soft mounds and delicate color provide a nice contrast to boulders and spiky desert plants, and look great in rock gardens or as an edging plant.

It is an important source of nectar for bees, butterflies, moths, and other insect pollinators. Birds like the seeds and desert tortoises enjoy the leaves and flowers.

It’s said to be resistant to deer and javelinas, but oddly rabbits enjoy it.

Why I Like This Plant

• Delicately beautiful pink flowers
• Stays evergreen in mild winters
• Low maintenance
• No thorns, low-litter, non-toxic
• Important food source for pollinators

Things to Watch Out For

Have you ever heard the sentiment “it’s a native plant, so it must be good“?

Mexican evening primrose is an example of why this statement is not always true. If you have a large area in mind, a place where you want to prevent erosion, or a difficult hillside to cover, this could be the right plant for your situation. It’s also a good choice if you have a hungry tortoise that can help to keep the plant’s growth in check.

But this delicate-looking plant can be surprisingly aggressive. Many gardeners regret having planted it, and I’m among them. The second year mine “took off” and I was horrified to find how far it had spread by underground rhizomes.

(If you have plants that you want to get rid of, you’ll find tips for eradicating Mexican evening primrose at the bottom of this post.)

Optimal Growing Conditions

If you’re thinking of adding a Mexican evening primrose to your garden, you need to find a suitable place that will keep your plant healthy and looking good.

Here are the key factors to keep in mind.

Temperature

Mexican evening primrose should be grown in USDA Hardiness Zones 5 – 9. They tolerate desert heat and extreme cold. Plants may die back in the winter but can survive temperatures down to a frigid -20℉.

In the heat of the summer, flowering tapers off and plants sometimes go dormant, especially if they don’t receive supplemental water. Plants can remain evergreen and flower all year during mild winters.

Sun Exposure

Plant evening primrose where it will receive full sun or light shade. They do well in the dappled shade under a tree but produce fewer flowers when not in full sun.

Size and Growth Rate

Mexican evening primrose grows moderately fast. When fully grown, each individual plant forms an attractive mound, typically 6 inches to 1 foot tall by 3 feet wide.

But it reseeds and aggressively sends out underground rhizomes and can easily take over an area if you let it.

Fun Fact!
In spite of its name,
Mexican evening primrose blooms during the day.
Each flower lasts just one day.

Soil

Mexican evening primrose grows in any desert soil — clay, loam, sand, or rocky — provided it’s well-draining. Plants can develop root rot in poorly draining soil.

Other Location Considerations

Mexican evening primrose has no thorns, stickers, or irritating hairs. Because plants are “unarmed,” non-toxic, and litter-free, you can feel comfortable placing them near a pool, sidewalk, or anywhere they might come in contact with pets or people.

Since it can grow aggressively, planting it where it can’t get too far out of bounds such as along sidewalks, patios, or driveways or surrounded by edging can be helpful.

If you really want one but are concerned, you can grow it in a container. However, they only flower for a few months and don’t look like much when not in bloom, so you might want to intersperse them with other plants.

Mexican Evening Primrose:
The Essentials

Common Name	Mexican evening primrose
Scientific Name	Oenothera speciosa
Origin	US Central Plains, Northern Mexico
Plant Type	Semi-evergreen ground cover
USDA Zones	Zones 5 – 9
Cold Hardiness	To -20℉
Flower Color	Pink
Flower Season	Spring, fall
Mature Size	1′ high x 3’ wide
Growth Rate	Moderate
Sun Tolerance	Full, part sun
Water Needs	Low
Pests & Diseases	Root rot
Garden Friendly	No thorns, low litter, non-toxic
Wildlife	Attracts bees, moths, birds, butterflies

How to Plant

The rule of thumb when planting any perennial in the desert is to dig a hole twice as wide as the root ball but no deeper. Amending the soil is not recommended. Counterintuitively, backfilling with the same native soil you just dug up helps your plant develop a stronger root system.

When to Plant

The best time to plant perennials is in the fall. This gives your plant three seasons to get established before the following summer.

The second best time is in spring, the earlier the better. This still gives your plant time to get established before the intense heat of June arrives.

How to Care for Mexican Evening Primrose

Whether you’ve recently planted a Mexican evening primrose or have an existing one in your yard, here’s how to take care of it to keep it healthy and looking its best.

How to Water

During the first growing season, give your plant about ½ gallon of water once a week while it’s establishing its root system.

After that, the University of Arizona recommends watering perennial ground covers on this schedule:

Spring (March – May)	10 – 14 days
Summer (May – Oct.)	7 – 10 days
Fall (Oct. – Dec.)	10 – 14 days
Winter (Dec – March)	14 – 21 days

When plants don’t get enough water, they can go dormant in the summer. When given too much water, they can develop root rot.

Pro Tip!
Giving established plants minimal water
helps to control their rampant growth.

Should You Fertilize?

Mexican evening primrose does not need to be fertilized. As a native plant, it has evolved to get all the nutrients it needs from desert soil. And there’s no need to stimulate the growth of this already vigorous plant.

How to Prune

Mexican evening primrose is usually cut back in spring, late summer, or fall but you can trim it anytime you want to keep its size under control. You can trim away any cold damage in the spring as soon as new growth appears.

How to Get Rid of Mexican Evening Primrose

I’ve written over 120 plant profiles on how to grow desert plants. This is the first one that includes advice on how to get rid of it.

Here’s what worked for me.

First, I pulled out the original plant — thank goodness I only planted one! Then I kept digging further away from the plant, pulling out any rhizomes I found. I caught it early and the rhizomes stopped at about 4 feet away in every direction from the original plant.

I quit watering the area and then checked daily for any new sprouts for several weeks and gave them a yank.

Occasionally, new sprouts popped up where I couldn’t grab hold (such as directly under a barrel cactus).😖 In that case, I protected the nearby plant with a piece of cardboard and sprayed the sprout with straight vinegar during the hottest part of a sunny day. If that hadn’t worked, I would have used herbicide, but I didn’t find that necessary.

I was lucky. No new growth appeared — I got it all during the first season. Phew! Not everyone is that lucky. I know gardeners who have been trying to get rid of it for years. It’s especially difficult to eradicate if it spreads into a lawn or among other ground covers or perennials.

Plant Lover Facts

Mexican evening primrose goes by many other common names including pink evening primrose, showy evening primrose, pink ladies, and pink buttercups.

There are many discrepancies regarding its native range. According to the Lady Bird Johnson Wildflower Center, it’s only native to the central grasslands from Missouri and Nebraska south through Kansas, Oklahoma, and Texas to northeastern Mexico.

But according to the Kew Gardens database, its large native range also includes Arkansas, Indiana, Iowa, Louisiana, and New Mexico.

Because its range overlaps with parts of the Chihuahuan and Sonoran Deserts, I consider it a southwest desert native.

Invasive or Aggressive?

You may notice that I intentionally use the term “aggressive” rather than “invasive”. Technically, for a plant to be considered invasive, it must spread aggressively outside of its native range and cause harm to its new habitat. I’ve not found any evidence that it harms the environment if it escapes cultivation. But it sure can be a headache for desert gardeners.

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Photo Credits

Siris603, CC BY-SA 4.0, Wikimedia Commons

Chihiro H, CC BY-SA 3.0, Wikimedia Commons