Romneya coulteri

( ROM - nee - uh      cull - TOO - ree )

At-A-Glance Information

This shrubby perennial is commonly called Coulter's Matilija Poppy or California Tree Poppy and needs full sun and little to moderate water. These plants are native to the coastal mountains and valleys of Southern California and Baja California, Mexico, and reach 6-8 feet tall. Leaves are grey-green and flowers are white with gold centers. These shrubs are great for hillsides, sloped areas and in marginal areas or wide borders, and produce some of the largest flowers of any California native plant, aside from  The genus Romneya, named for Irish astronomer John Thomas Romney Robinson has two species, and is a member of the plant family Papaveraceae. The specific species epithet coulteri pays homage to the Irish botanist and explorer Thomas Coulter. California Tree Poppy grows well in zones 4-12, 14-24 and H1 (to find your zone, click here: Zone Map).

Caring for and pruning romneya coulteri shrubs

Plant Romneya coulteri in full sun (it should be getting at least 6 hours of direct sun each day) in well-draining soil that is acidic to neutral. These shrubs prefer a pH of between 5.0 and 8.0, and if your soil is clay or heavy, it should be amended with plenty of organic matter before planting. Water regularly during the growing season and while the plant is getting established in its new home. At maturity, these shrubs are considered drought-tolerant, but do like deep waterings during the warmer months of the year. Mulch around the base of the plant to increase soil moisture retention. These plants do not require heavy feedings to perform well; if they are struggling apply a balanced, slow-release fertilizer in springtime. Prune to maintain shape and remove dead foliage or branches and spent flowers in late springtime. If the plant needs a rejuvenation pruning, In autumn cut the whole plant nearly to the ground; new shoots will start to emerge in late wintertime, and the shrub will bounce back completely in springtime.

Propagation

Romneya coulteri can be propagated either by using root cuttings or from seed. To ensure that your propagated plant will have the exact same qualities and characteristics as the parent plant, use the cutting method. If you would like to experiment and see what plant you can grow from seed, just keep in mind that it will not necessarily be the same as the parent plant. To propagate your shrub, follow the instructions below:

Propagating Romneya coulteri by Root Cutting
Root cutting should be attempted only when the plant is not in its blooming period. To use this method, you will need a clean shovel, clean pruning saw, extra pots, and well-draining soil to fill the pots. Your soil should be amended with some sand to increase drainage. To propagate your shrub by root cutting, follow the instructions below:
  1. Identify the plant you're going to take your root cutting from. Ensure that the plant has had a good watering the night before, as this will increase the odds that your root cutting will take.. Start by loosening the soil around the plant with your shovel, working your way inward to avoid causing damage to the roots. Once you've gotten your clump out of the ground, lay it out on its side.
  2. Identify a root (or a few roots, if the plant is a large size) that you'd like to use. The root should have at least 4-5 nodes on it. Lay them out on the ground. Then, cut the root segments into 2-3 inch pieces, with the nodes in the center of the pieces.
  3. Fill your pot(s) with sand-amended soil about 3-4 of the way up, and then place your cutting on top. Cover with about a half inch of soil. Water generously and ensure that adequate drainage is occurring. Place the pot in an area that receives bright, indirect light and stays at a temperature of around 70 degrees Fahrenheit. Your root should begin to grow a new plant in about 3-5 weeks.

Propagating Romneya coulteri by Seed
  1. Keep in mind that the plant you get from seed will not necessarily mimic all of the characteristics of the parent plant. To propagate by seed, you will need a paper bag, a pot or tray filled with well-draining compost or other organic material, a spray bottle and a fork. If you don't have any potting medium on hand, you can make some. Just mix together equal parts (by volume) moss peat and horticultural-grade sand or grit sand. You will also, after a few weeks, need individual 3-inch pots for each seedling that grows.
  2. Water your prepared seed tray or pot filled with soil, and ensure that good drainage is occurring. Place your seeds in your prepared pot or seed tray about a quarter inch to a half-inch under the soil surface. Cover them with soil and water with your spray bottle. Place your tray of seeds in a warm area that receives bright, indirect light. A greenhouse is the most ideal climate, but a planting tray inside a window will do as well. Germination usually takes 7-14 days from sowing. Once you begin to see seedlings sprout and they are able to be handled, transplant them to their own individual 3-inch pots, filled with the same potting medium as described in Step 1. Loosen the seedlings from the potting medium by digging down with the tines of your fork about an inch and a half, gently working the seedling up until it is out. Then, replant the seedling in its individual pot.
  3. Keep the seedling's potting medium moist, but not wet, by spraying the soil with your spray bottle. Keep your new plant in an area with bright light (though not direct sunlight) and temperatures between 55 and 70 degrees Fahrenheit. Ensure that the soil stays moist, but not wet, until the next spring (after the danger of frost has passed), when you can transplant it to its new home.
Romneya coulteri seed heads are left behind after flowers have faded, and will begin to release seeds once they have dried out.
Romneya coulteri seeds.

Problems and Pests

Romneya coulteri shrubs are generally pest and disease-resistant, but can occasionally have issues with:
  • Aphids
For information on these pests, including how to eradicate them, see the links below:
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Gallery

Plant Romneya coulteri with other low water-use plants.
Tree Poppy foliage is attractive, with deep cuts in the leaves. Zone 17.
Date: May 6, 2023
I came across a bee sleeping inside the safety of a Tree Poppy flower on a walk in zone 17.
Date: May 6, 2023

Videos

All about Matilja Poppy.
Tips and tricks for growing these shrubs.
How to propagate Romneya coulteri.
Learn about these California native plants.
How to support Romneya coulteri shrubs.
How to prune California Tree Poppy shrubs.

Resources

Romneya - Growing Guide
Wikipedia: Romneya
Wikipedia: Romneya coulteri
The New Sunset Western Garden Book: The Ultimate Gardening Guide (2012) - Page 567, Romneya coulteri
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