Romneya Coulteri: A Giant California Tree Poppy

Ed Wike
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Romneya Coulteri Overview

Romneya Coulteri is a strikingly beautiful flowering plant that is mainly native to California. In some ways, it is a very unique plant. It is evergreen and it is a perennial, which means that it can retain its leaves during the dry and sunny summer months. It is also able to retain its leaves through the drier winter months.

In the wild, it grows in a variety of different areas, ranging from the coast to the mountains. It can often be seen growing alongside the coast near the sea, while it also does well in dry and rocky soil, if there is plenty of sunlight. Seedlings need sunlight to grow, so it doesn’t do well in shady areas.

Its botanical name is Romneya Coulteri, which was named by John Torrey in 1840. It belongs to the family of the Ice plant. Since there is no true Latin name for this plant, it is also sometimes referred to as ¡¤the weed that eats concrete¡¥ or ¡¤the concrete weed¡¥.

There are a lot of different things that make Romneya Coulteri unique. The main characteristics that can be seen, are its large and colorful flowers. It can grow up to five feet high and it frequently yields buds that can reach a width of over six inches, which is simply remarkable.

All About Matilija Poppy, Romneya Coulteri

Easily one of the most beautiful California flowers, Mormon tea, or tree poppy (Romneya coulteri), was named by the famous botanist, David Douglas. It is now a federally endangered species. Producing a spectacular yellow trumpet-shaped flower in late spring, this white petaled flower is a California native. It is also known as the “California Desert Poppy” and the “Matilija Poppy.” With its ingenious way of attracting pollinators, this is one of only 15 genera in the poppy family.

Caring For Coulter’s Matilija Poppy

The Coulter’s matilija poppy is the official state flower of California, and you can see why when you look at it up close. It is a stately, garden-worthy perennial that is easy to care for and a great choice for people who live in the hot, sunny southwestern regions. The giant poppy species are as appealing as they are easy to grow, and one of the best is the Coulter’s matilija poppy.

Coulter’s matilija poppy (Romneya coulonis) is the most well-known of the giant poppies. It is a perennial that can grow up to six feet tall, and it casts a massive shadow when planted in the right location. The flowers are bright orange and attract hummingbirds, butterflies, and bees. The matilija poppy blooms in early spring, with flowers that may reach more than five inches in diameter. This flower’s petals are thick and waxy, and they will stand up to the hot, dry summer winds, which keeps the bright orange flowers lasting for several weeks.

Light & Temperature

Romneya coulteri requires a warm sunny spot protected from the wind to bloom. Plant it in a sunny area but don't plant it in the full sun. Under these conditions, poppies will bloom from April through July.

Romneya coulteri likes an alkaline soil that is just slightly moist. Use peat moss or pine bark for the best results. Weekly watering is usually enough. Weekly fertilization is also a good idea with a good all-purpose fertilizer. If your Romneya coulteri begins to look like it is dying, you can try misting the leaves to encourage growth. Also, to get your bloom pattern to form, the plant should not be watered for about a month before bloom.

To get the best bloom possible, it is important to prune your plant. To do this, wait until you see the plant setting buds. Then, with a sharp blade, cut the whole top off the plant. This causes the focus to shift to the buds. For an even larger bloom, cut the top and side stems right above a node. You will get the largest bloom with this method.

Water & Humidity

The Romneya can tolerate periods of drought, but overwatering and underwatering are often fatal for this perennial. The best way to water the Coulteri is to use a drip system or a soaker hose to target the roots. Keep soil evenly moist during its growing season, but let it dry out between waterings.


It flourishes during the summer. During the hot summer months, the woody stems of this full-sun perennial become densely covered with a profusion of bright, yellow flowers. It is best planted in sunny sites in well-drained soil. It is drought tolerant.

Growing a mature plant requires patience (approximately 14 years) and adequate space, but it is a carefree plant that is a necessity for the desert landscape-gardener. In bloom it attracts butterflies and hummingbirds. For best growth, shade the plant during the summer and keep the soil consistently moist.

Even if you do not have a need for this plant, you will surely want to pass along cuttings, because poppies grow easily from seed. The poppy plants are easily grown from seeds—just press the seed against the soil surface, press the soil against the seed, and water lightly.


California Giant Tree Poppy is generally grown as a container plant indoors; however, some gardeners may opt to grow this plant outdoors when the plant is mature. The plant may grow 6 feet tall if grown outside. The color of the flowers range from bright yellow to orange, and the flowers may be used as cut blossoms for home decor. The plant does not need a lot of nutrients for its development, but does need the proper amount of water. Once the plant matures, it is possible that it will flower in the home on its own; however, if this does not occur, someone will need to help the plant bloom.

The California Giant Tree Poppy can be fertilized several times during the season. However, do not fertilize when the plant is already blooming for the season as fertilizing will only cause the plant to blossom more frequently and in an abundance that will be difficult to manage. In the spring, the California Giant Tree Poppy will benefit from a fertilizer with high nitrogen, such as high-analysis 10-10-10.


Romneya Coulteri: Repotting Advice

Repot this plant when you see roots growing out of the drainage holes in the bottom of the pot. The goal here is to keep the plant healthy and prevent it from being pot-bound.

When potting your tree poppy, use a container that is just a few inches larger than the one the plant is currently in. Fill the new pot with a potting mix that contains compost in it. Although you can purchase expensive potting soil specifically for cactus, a very good option is to use topsoil that contains compost added to it. And you can add a slow-release fertilizer to help your plant grow well. Your local nursery should have this type of potting mix and fertilizer.

In autumn, when the plant's growing cycle slows for the winter, it's a good idea to remove the faded blooms and also the older leaves. This will keep your tree poppy looking vibrant for a long time.

In the spring, after the new growth has started, you can prune off the older growth. This will help you control the size of your plant.

When it comes to caring for your tree poppy, you're in for one great ride with this one. Your plant is gorgeous and this is an easy cactus to care for.


In the wild, this stunning species has been reduced to less than 20 populations in about 10 locations. The range of these populations is rather small, with most of them measured in acres, not square miles. The populations are often localized to single canyons or slopes and are dangerously close to extinction. Even though species in this genus are traditionally not as prone to disease as many other members of the Papaveraceae, Romneya Coulteri is not immune to the ravages of cattle. Of all the factors that threaten this species, cattle grazing is perhaps the most damaging.

This is because Romneya Coulteri's deeply forked, grayish-green foliage is so abundant that it provides an attractive target for cattle to trample and munch. Cattle are also fond of the leathery-green seed pods, which provide an easily-accessible source of nutrition for the cattle. By the time a seedling reaches five years of age, it may have already lost its ability to reproduce.


You will find that the Romneya Coulteri grows best in a mixture of equal parts sand and peat moss with a liberal amount of fertilizer added to the potting soil. Along with this combination of ingredients, you must also water the plant regularly as well as fertilize the soil and the plant itself with a high-nitrogen fertilizer.

Be sure to plant the Romneya in an area that has plenty of sunlight. Like other succulents, the Romneya Coulteri is a very drought-tolerant plant, so you shouldn't have to water the plant very frequently. As long as it gets full sunlight.

If you notice that the leaves of the Romneya are becoming discolored, striped, or otherwise mottled, you may want to take the plant into your kitchen, and wipe both sides of the leaves with a damp, clean sponge. This will help to give the plant a fresh new start. Be sure not to allow the Romneya Coulteri to become overly wet.

If you are adding fertilizers to the soil, then you should test the soil with a nutrient-testing kit before adding any additional fertilizer to the plant. This will ensure that the Romneya Coulteri is receiving the proper nutrients that it needs.


Mature poppies can look a bit different than when they are first planted. As they mature, they can look lankier, greener, paler, sickly, and even have crispy or brown tips.

These aberrations seldom indicate a plant is "dying" but the gardener might feel uncertain. To ensure your garden poppies are healthy, look for:

Healthy, firm, green foliage.

Resilient stems and stems that don't snap off.

A color that shows a "fruit" with light to medium green with white, contrasting veins and purplish pink petals.

The petals need to be crisp and not browned or rubbed off.

If you do think your poppy is looking sickly, you might notice browned, paper-like, or leaf-like growth on the poppy seeds. This is usually harmless, but remove all the seed pods with the browned growth inside to minimize the spread.

If you think your poppy is suffering from a chemical reaction from fertilizers or pesticides, wash the leaves and stems well with clear water and let the whole plant dry under the sun. If the color doesn't return or your plant appears generally unhealthy, take it to a water garden plant specialist to be sure!

Growing Problems

Unlike a rose or a lily, the giant, orange-red, trumpet-like flowers that grace the branches of the shrub 'Romneya coulan' are part of the poppy family. This Shrub, Romneya Coulteri, or more often known as the California Tree Poppy, is a native plant of coastal California and Baja Mexico.

A fast growing, awesome, flowering beauty, this plant will flower in late spring until it gets cold-weather damage or until temperatures fall below 30 and it enters a dormancy period. It comes back in the fall and blossoms up until the winter cold hits. Many gardeners simply let it over winter on their properties in pots so they can enjoy the spring flowering and then move it to a greenhouse for the winter.

Romneya is an outdoor plant (as long as you have lots of space for it!) It grows on other plants and is usually badly damaged if you try to move it indoors, though in rare instances, it has been known to flower indoors. It does very well outdoors in California but may require a greenhouse in other states. It grows vigorously and can be trained against a wall on a trellis or pruned so at least one side (preferably at least two sides) is neatly branched. In good conditions (full sun to partial shade, little or no frost and mild winters) the plant will grow up to 15 feet tall.


When you discover that your “empty” plant is experiencing insect activity, it’s an easy assumption to make that you have an infestation. Pests and diseases are different, so your remedy may be different as well.

To attack the issue in the most effective way, you’ll need to do a bit of detective work.

Diseases are caused by a variety of factors that affect the health of the plant. They often do not have a predictable cycle in which they are active. It is important to determine the cause of the disease to know how to treat the problem.

Here are some of the more common symptoms of disease:


Frequently Asked Questions

Mitt Romneya Coulteri is a robust, California native tree poppy that is known for its striking orange-red flowers, large size and fast growth rate.

If left untended, the poppy can grow to an erect tree height of 25 feet, with a spread of 10 to 12 feet. But if pruned and kept trimmed, the tree can be kept as a shrub and maintain an optimum height of 6 feet. The most common use for this plant, however, is as a tree or a fast growing, large shrub.

How Big Do They Grow?

Like many other plants in the Amaryllis family, Mitt Romneya Coulteri has a large bulb or tuber. And this makes it one of the easiest plants to grow in the San Diego region.

The flowers and leaves emerge in spring, and the flowers will continue to bloom until it reaches maturity in late fall. The total flowering cycle generally lasts for 40 days. If the plant is allowed to remain in bloom for several years, the bloom cycle will become shorter.

The flowers are eye-catching, and they will grow from the center of a hollow, smooth trunk that is about 10 to 15 inches in diameter. The leaves are divided or lobed into about three parts, and they can grow to lengths of 10 to 12 inches.