California tree poppy (Romneya coulteri) is a flowering perennial herb that attracts bees and butterflies. California tree poppy becomes dormant in the summer and is considered low maintenance to cultivate. This species grows in dry, rocky and sandy soils.
I. Appearance and Characteristics
Romneya coulteri, the Coulter’s Matilija poppy or California tree poppy, is a perennial species of flowering plant in the poppy family Papaveraceae. Native to southern California, USA, and Baja California, Mexico, it grows in dry canyons in chaparral and coastal sage scrub plant communities, sometimes in areas recently burned. It is a popular ornamental plant, kept for its large, showy flowers.
The specific epithet coulteri commemorates Thomas Coulter, an Irish botanist and explorer.
This herbaceous perennial may exceed 2 m (7 ft) in height, its stem growing from a network of rhizomes. The gray-green, waxy-textured leaves are each divided into a few lance-shaped lobes, the blades growing up to 20 centimeters (7.8 in) long. The inflorescence is a large, solitary flower with six crinkly white petals each up to 10 cm (4 in) long. At the center of the flower is a cluster of many yellow stamens. The fruit is a bristly capsule, 3–4 cm (1–2 in) long, containing many tiny seeds.
This plant often grows aggressively once planted. It spreads clonally by underground rhizomes and can appear several feet away from the original plant.
This plant bears the largest flowers of any species native to California, rivaled only by Hibiscus lasiocarpos. It was nominated for the honor of California state flower in 1890, but the California poppy won the title in a landslide.
In cultivation in the UK, Romneya coulteri and the cultivar ‘White Cloud’ have gained the Royal Horticultural Society’s Award of Garden Merit.
II. How to Grow and Care
Sunlight
To reach their full height and flowering potential, these plants need full sun exposure. They will grow in dappled shade, but the brilliant golden color of the yellow centers is brightest with full sun exposure.
Temperature and Humidity
Matilija poppies thrive in dry conditions and warm temperatures. Their hardiness zone is fairly narrow (USDA 8 to 10), which usually indicates a plant that likes very specific growing conditions. If your growing zone hovers between 7 and 8, you might be able to get these to overwinter by mulching them heavily. If you can mimic the plant’s native growing conditions, this may be a plant you can enjoy in your yard. But with the matilija poppy, ideal growing conditions also means the plant can become invasive.
Watering
The best watering practice is to try and mimic native desert watering conditions; that is to say, as if an occasional hearty rainfall occurs every few days. Once a week is reasonable, perhaps every five days or so if growing in containers. It’s okay to let the soil dry out a bit between waterings, as this plant is very drought resistant. You’ll know to give it supplemental water in addition to your regular schedule when the plant starts drooping. Overwatering will cause leaves to discolor and flower petals to fall prematurely. Mulching to ensure even moisture may also be helpful.
Soil
Being native to dry, arid, desert climates, the matilija poppy prefers dry, sandy soil. It requires good drainage, so clay soils might require amendments. Otherwise this flower is fairly tolerant of diverse soil conditions.
Fertilizing
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.
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.
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.
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.
Pests and Diseases
- 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.
III. Uses and Benefits
The large, lovely blooms of Matilija poppy make it perfect as a decorative addition to informal cottage gardens, or even as a vibrant pop of color in Mediterranean gardens. It makes a lovely showy flower in its own flower bed or along the borders of a garden. Even though some common garden pests like to snack on it, it’s resistant to deer.