Romneya Coulteri: A Giant California Tree Poppy

Romneya coulteri, also called matilija poppy, is a gigantic California native and great for large-area xeriscaping. We'll share all our tips!

Romneya coulteri

Contents

If you’ve ever looked out across the mountains in southern California, you may well have seen the matilija poppy, Romneya coulteri. Also called Coulter’s matilija poppy or California tree poppy, this gigantic plant was once among the contenders for California’s state flower! Alas, it lost to another form of poppy.

But this California native perennial is still quite popular today as an erosion control plant on hillsides. It’s also seen growing in foothills or canyons, sometimes as one of the first plants to reappear after a brushfire has passed.

You won’t see this in little cottage gardens. It’s just too big to add to most residential yards. But it works beautifully in xeriscaping!

So let’s talk about this lovely California chaparral plant in more detail!

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Romneya Coulteri Overview

Romneya coulteri
Romneya coulteria, the California tree poppy, is a massive native plant. Source: jacksnipe1990
Common Name(s) Coulter’s matilija poppy, California tree poppy
Scientific NameRomneya coulteri
FamilyPapaveraceae
Height & Spread6′-8′ tall and wide
LightFull sun, tolerant of partial shade
SoilWell-draining sandy soil, mulched to prevent moisture loss
Water:Drought-resistant but prefers 1″ of water per week
Pests & Diseases:Caterpillars, occasional powdery mildew, some rhizome rot.

All About Matilija Poppy, Romneya Coulteri

One of the most remarkable aspects about this plant is its flowers. Sometimes nicknamed fried egg plant, flower size is between 4″-9″ across and it does in fact resemble a fried egg. Large, soft white petals surround a gorgeous golden yellow center with the slightest apricot aroma. The fried egg name doesn’t do justice to this gorgeous bloom!

Sharing a genus with a related plant, the coulteri Romneya is easily confused with its sibling. Romneya trichocalyx has smaller flowers and fruit than its gigantic coulteri relative, and hairy sepals and stalks. More importantly, it’s not 8′ tall.

It grows in a rather bushy fashion, its long branches heavy with 8″ long grey-green leaves. Plants cluster together, attached by a spreading rhizome system beneath the soil’s surface. This network of rhizomes can creep up to 20 feet from the original plant, and if they’re not controlled can become invasive.

Flowering from late spring through early summer, the stems will be tipped with 5-8 gigantic flowers each. The white petals are often rippled or crinkled like crepe paper. As the flowers fade, the center forms an inedible fruit as its seed pod. It can self-sow in fall once the seeds have ripened.

Its name, Romneya coulteri, is in honor of Dr. Thomas Coulter, a botanist who collected the plant. It’s native from southern California down into Mexico. It is often found around chaparral and coastal sage plant type communities. It is deer resistant and tolerant of drought conditions.

While there are few commercial cultivars, a hybrid called White Cloud is said to have less aggressive spreading characteristics than other Romneya coulteri species.

Caring For Coulter’s Matilija Poppy

Coulter's Matilija Poppy
Coulter’s Matilija poppy can produce flowers up to 9″ across. Source: Monkeystyle3000

In its native range, this plant gets no care at all and thrives. As a landscape plant, you’ll likely want to encourage it to stay within certain boundaries and encourage flowering. So let’s go over its optimal growing conditions!

Light & Temperature

Full sun is perfect for this plant type. While it can take dappled shade, it needs lots of light to produce its white flowers with their pop of yellow color.

It’s able to stand typical southern California heat with no problem at all, but like many native to California plants, it dries out during the summer. This plant is deciduous during the late summer months and will drop many of its leaves from then through fall.

It goes dormant in winter. If there’s enough leaf mulch over its root system, it’ll pop right back to life in the spring. Generally, the plant is frost hardy down to 23° F (-5° C).

Water & Humidity

Once it’s established, you should never need to irrigate your Coulter’s matilija poppy again. No, I’m not kidding. In the wild, it gets annual rainfall between 11″-40″ per year and does just fine. It handles low water conditions extremely well.

As a young plant, it does need a little more water. Mulch around the plant to keep moisture from evaporating out of the soil. This is all you need to do to provide the proper ambient humidity.

Soil

Sandy to gravelly soil with a pH range between 5-8 is ideal for this plant. It must be very well draining, or else the rhizomes are at risk from fungal-based rot. If you’re working with heavy clay soil, amend heavily with compost and agricultural sand, or perlite.

Fertilizer

Fertilizer is not needed for this plant. It may be helpful when the plant is very young, but it’s just not necessary. If you fertilize, it may affect the overall performance of your tree poppy, so avoid it.

Repotting

Due to its tender rhizome structure, this plant is not a good candidate for container growing. Plants purchased from a nursery should be planted directly in the soil. Do not attempt to container grow and repot. Disturbing the rhizomes can result in plant death if you dig them up in the active part of the growing season.

Propagation

During the winter, rhizomes can be carefully separated and replanted. This only works while the plant is dormant, and can be fatal to the plant at other times of year. Propagation by seed is difficult, as seeds only germinate after a fire.

When you remove the rhizomes, ensure you have a site prepared for planting elsewhere. It should be a sandy loam that is very well-draining.

Pruning

In California, Romneya coulteri should be cut back to 6″ above the ground in late summer or in the fall. The cut back material makes excellent mulch for the rest of the plant and should be applied around the plant’s base.

Troubleshooting

If this plant sounds too good to be true, it’s not – it’s really that easy to care for! But let’s talk about the rare troubles that may arise.

Growing Problems

In the late summer, Romneya coulteri is deciduous and loses its leaves. It dries out during the summer months and can become a fire hazard in fire-prone areas. If you live in a fire-prone area, be ready to take it down once it goes dry and dangerous.

Pests

Some forms of caterpillars will chew on the leaves. While this won’t harm the plant, it may increase local caterpillar populations and put other plants in danger. Bacillus thurigiensis spray will eliminate this concern.

This plant is deer resistant.

Diseases

Powdery mildew can strike the leaves. You’ll be able to tell that powdery mildew has infected your tree poppy when the tops of the leaves look like they’re covered in a white dust. If you can remove these leaves without taking more than 1/3 of the foliage, do so. Then treat the rest with neem oil.

If your soil doesn’t drain well, the rhizomes may also be susceptible to fungal root rots. There’s no cure for this, so prevent the issue altogether by ensuring your Romneya is planted in well-draining, sandy loam.

Frequently Asked Questions

Q: Is Romneya Coulteri poisonous?

A: Yes and no. The Chumash used this plant as a traditional medicine, but it contains mild saponins that can cause skin irritation and gastric issues. Wear gloves when working with this plant.

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