Romneya coulteri

oooOIOooo via pbs pbs@lists.pacificbulbsociety.net
Sat, 15 Sep 2018 16:02:53 PDT
I ask Californians for some information on this huge poppy with some trepidation. It isn't in our photographs section. It doesn't have a bulb, just large tapering roots, like Ranunculus, which is in our Wiki. However, it is Pacific, and it does come back in fall from a large underground water storage system.

I see it in California freeway landscapes, on slopes that did not exist before road construction. (Or did it sprout naturally?) I have seen it growing wild, in the grassland and oak zone, along Highway 74 east of San Juan Capistrano in Orange County. (There are beautiful Dudleya pulverulenta along this road, as well.) I have seen it in the canyons of Saddleback Mountain in the same region.

For decades, the Sunset Book has said this is suitable for Sunset Zone 13, where I live in Phoenix. But, nor I nor more experienced plantspeople have been able to get it through the first summer after fall planting. I visited Orange County over Labor Day and couldn't resist buying another plant in a 1 gallon / 3.79 liter can at Green Thumb Nursery off Interstate 5 at El Toro Road in Lake Forest. The plants were the largest I've seen for sale in 1 gallons. They look like they are grown from root cuttings: There is a horizontal piece of root at the soil surface, from which leafy tops have sprouted. The soil was moist at the nursery. I will wait to plant it until nights are cooling down, and for now I am giving it only a few hours of late afternoon sun, keeping the sun off the container. I am also watering sparingly, just when it is near wilting.

Our late fall, winter and early spring are probably great for this plant. We get occasional light overnight frosts and gentle winter rain, as along the coast. We get a lot less winter rain than coastal California has experienced in the past, so I will probably need to provide supplemental winter irrigation. In late spring and early summer we have the hottest temperatures, 110+ / 44C+; it does not rain, and humidity is very low, something like really bad Santa Ana conditions without wind. From mid July on we have lower temperatures, usually in the mid 100s / 38-42C, and somewhat higher humidity when it is not raining. We get sporadic thunderstorms with dramatically lower temperatures and heavy rainfall during this time.

So, my questions:
Does CalTrans provide summer water for some landscapes in the Orange County and San Diego areas, where I have seen this planted along freeways? Is it evergreen in California with summer water?

Is it better to give some summer water the first year? Will our normal monsoon rain probably be enough? Or should I protect it from rain?

Would it be better to plant it in rocky soil, or in deeper soil? In California I have only seen it on deep soils, not rocky areas, but I haven't hiked everywhere. A rocky area here would dry much faster after a monsoon rain during the warm summer dormancy, but also in the cool growing season.

Has anybody seen it growing in anything other than full sun all day in California? A lot of full-sun plants from elsewhere tolerate our heat better with morning sun and afternoon shade, or dappled shade, as under a well-trimmed mesquite.

When I plant it, should I bury the exposed root cutting?

If the tops don't die down next spring, should I cut them off? Or should I let it die back normally?

Should I cover the root zone with something to keep the sun off the soil?

Do they always die back in summer?

Thanks,
Leo Martin
Phoenix Arizona USA
Zone 9?

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