Romneya coulteri
The California tree poppy, Romneya coulteri, is a woody perennial in the Papaveraceae family native to the coastal scrubland of southern California and Mexico’s Baja California.
It is suited to cultivation in Zones 8 to 10. The species grows readily in soil recovering from wildfire damage, and is a water-wise choice for xeriscaping with native flora.
It is also known as Coulter’s Matilija poppy, which honors 19th century Chumash tribal leader Chief Matilija and Irish botanist Thomas Coulter, who explored its native habitat and collected plant samples for Trinity College in Dublin.
Home gardeners delight in the golden-centered, slightly fragrant, crinkly white blossoms measuring up to eight inches across and resembling ruffly fried eggs.
You’ll find all you need to know to grow and care for California tree poppies in this guide.
Here’s what I’ll cover:
California tree poppies sport grayish-green lobed foliage and thick stems, growing to heights of six to eight feet with an equal spread.
In the warmest regions, the leaves are semi-evergreen. Where it is cooler, they turn brown and die at season’s end.
Prolific spring and summer blooming adds substantial vertical visual appeal to climactically suitable landscapes.
The bristly Matilija poppy, R. trichocalyx, is a related species often crossed with R. coulteri to breed ornamental hybrids.
Quick Look
Common name(s): California tree poppy, Coulter’s Matilija poppy, fried egg plant, Matilija poppy
Plant type: Perennial subshrub
Hardiness (USDA Zone): 8-10
Native to: California and Mexico
Bloom time / season: Spring, summer
Exposure: Full sun
Soil type: Sandy loam, organically-rich, well-draining
Soil pH: 5.0-8.0, slightly acidic to slightly alkaline
Time to maturity: 1+ years
Mature size: 6-8 feet tall and wide
Best uses: Massed in drifts
Taxonomy
Order: Ranunculales
Family: Papaveraceae
Genus: Romneya
Species: Coulteri
R. trichocalyx differs from our subject species because it has slightly smaller flowers, narrower leaves, and bristles on the calyx below the petals and the upper stems.
California tree poppy is as bold as it is beautiful, the plant is able to withstand strong sea breezes.
When established, the plant increases its landscape footprint with vigor, spreading via rhizomes and by self-sowing.
Choose a location where it can spread into a large drift, or display it on a hillside where the shrub can help control soil erosion.
How to Grow
California tree poppy plants are slow to become established, often failing to bloom – or blooming sparsely – at first.
Once established, they flower profusely, are drought-tolerant, and require little maintenance.
Gardeners are most likely to achieve success when they meet the following cultural requirements:
Light
Provide a location with full sun or the dappled shade of deciduous trees to support robust blooming.
Soil
The soil should replicate the species’ native growing environment and consist of organically rich, sandy loam that drains well.
The ideal pH is between 5.0 and 8.0, or slightly acidic to slightly alkaline.
Water
Provide an inch of water per week during the first growing season, in the absence of rain.
Thereafter, plants are drought-tolerant, as mentioned, and should not require supplemental moisture unless the weather is unusually hot and the dry spell prolonged.
Fertilizing
California tree poppy is a light feeder that doesn’t require fertilizer. However, some gardeners like to give it a boost in the spring.
If you choose to fertilize, use a slow-release granular product with an NPK ratio of about 5-10-10.
Products lower in nitrogen help to support flowering without promoting an overgrowth of foliage.
Apply it sparingly to the soil around, but not touching the stems. Water immediately after application to dilute and disperse it.
Cultivars to Select
There are several cultivated varieties from which to choose, including:
Butterfly
‘Butterfly’ is a cultivar with exceptionally ruffled snow-white blossoms, fluffy yellow centers, and a generous eight-inch diameter.
The foliage hints of blue, further distinguishing it from the species.
White Cloud
‘White Cloud’ is a hybrid cross between R. coulteri and R. trichocalyx with the signature bristly calyx of R. trifchocalyx and crinkly six-inch blooms.
The density of the growth and the bloom period are somewhat longer than those occurring in nature.
In addition, gardeners will likely find straight species R. coulteri available for purchase in the appropriate growing Zones.
Maintenance
There are few maintenance chores when growing California tree poppies.
With its cultural requirements met, you can expect robust growth.
Because the California tree poppy spreads aggressively via rhizomes you may want to install an underground barrier to restrict root expansion.
Mass-planted specimens are generally self-supporting. However, you may find it beneficial to stake the outer stems to prevent leaning and possible breakage.
Deadheading spent flowers is optional, but it may prolong blooming. It also limits potential self-sowing.
In late fall, cut the stems down to four to six inches tall and dispose of the debris.
End-of-season pruning serves several purposes:
- Removes unsightly late-season foliage.
- Minimizes pest and pathogen breeding grounds.
- Allows gardeners to avoid having to prune old growth among new spring shoots.
Also, if spring shoots pop up outside your designated growing area, and you don’t want to use them for propagation, dig them up and dispose of them.
The more rootstock you dig up, the slower the spread.
Propagation
In the wild, smoke and fire naturally stimulate California tree poppy seed germination. In other regions, the species continues to thrive via root expansion.
Seed germination rates are low in the home garden and it can take several years for seedlings to reach maturity and start blooming.
California tree poppies can be easily propagated by digging up and transplanting suckers.
The plant produces many new shoots in spring which pop up on the fine roots that trail from the main rhizomes of mature plants. These can be dug up and transplanted.
Here’s how:
Locate a fresh spring shoot.
Push a hand shovel into the soil three to four inches away from the shoot and three to four inches deep. Bend the shovel slightly toward you to begin to lift the earth.
Work your shovel around the shoot in a circle, cutting and lifting, until you can unearth the soil containing the shoot.
Immediately transplant the entire clump of soil per the instructions below.
Transplanting
To transplant a potted specimen from the nursery, water it the day before.
Note its depth in the current pot.
Work the garden soil to a depth equal to the container and twice as wide. Loosen the soil until it is crumbly and free from debris.
If you wish to curb the spread of the shrub, you can install a root barrier at this stage to prevent the rhizomes from creeping outwards.
Unpot the plant and set the entire root ball in the prepared soil at the original depth, with the crown at or slightly above ground level.
Backfill with soil for a firm hold, and water in well.
Leave at least six feet between plants, and be prepared for aggressive spreading once established.
To prevent damage to the rootstock, avoid moving plants once they are in the ground. Broken roots left in the ground will likely regrow.
Pests and Disease
You should encounter few pests and pathogens with your California tree poppy. However, there are two that you should be familiar with.
Neoterpes edwardsata caterpillars are moth larvae that generally feed on bright orange California poppies, Eschscholzia californica.
However, when their favorite species is unavailable, they may eat California tree poppies.
The caterpillars are yellow or green with a gray band.
Adult moths have yellow upper wings with an orange to brown fringe and pale yellow lower wings.
You may want to think twice before handpicking and disposing of the foliage-consuming caterpillars because the moths are valuable pollinators that contribute to landscape diversity.
Powdery mildew is a fungal disease that favors shady, humid conditions. Temperatures between 60 and 80°F favor spore germination and dispersal.
Symptoms include leaf distortion and discoloration, followed by fuzzy grayish-white merging patches. The foliage often looks like it’s covered in a white flour coating.
Prevention measures include planting in full sun and not overwatering – if you do need to water, do so at soil level to avoid wetting the foliage.
Treatment with organic neem oil may prove effective if symptoms persist.
Learn more about how to deal with powdery mildew here.
Meeting cultural requirements results in healthy plants equipped to withstand minor infestations or infections.
Magnificent Matilija
The California tree poppy offers Zone 8 to 10 gardeners the opportunity to grow a high-impact flowering perennial that commands attention.
Do you have the perfect place for magnificent Matilija to roam through your spring and summer landscape? Why not take out your garden planner and get started?
If you grow California tree poppies in your landscape, we’d love to hear about it in the comments section below!
And for more information about growing other types of poppies and native plants, have a read of these guides next:
