PCI grow around the world. They naturally do the best in similar climates, which are those with World Hardiness Zones 10-7 and cool Mediterranean rainfall patterns, which means dry summers.
The appended references are a sampling on each topic, available in SPCNI Almanacs, 1973 to present. All back issues of the Almanac are available from SPCNI on a CD with an index (subject, author and by issue), for those who want to refer back to the original letters, notes and articles.
Excellent areas to grow PCI include: The British Isles, southwestern Europe (France, Portugal, Spain) and around the Mediterranean Sea, South Africa (cooler winter-wet areas of the Western Cape region at higher elevations), and parts of New Zealand and Australia. A member near Mexico City, Mexico found that with additional shade and summer water, PCIs did well at 7,000 ft.
While SPCNI has no reports of growers from South America, PCI should do well in this continent’s summer-dry areas, such as coastal Chile, south of the Atacama Desert and north of Patagonia.
Outside the West Coast, start plants from seeds if nurseries in your area do not have PCI for sale. Select the healthiest seedlings to plant out in your garden. Use your garden’s microclimate to select seedlings that prefer your area’s local microclimate, and develop your own local varieties of PCI.
Pay attention to soil acidity, water acidity, sun exposure, and soil drainage, referring to the first Growing PCIs section for guidelines.
Starting with species rather than hybrids may aid success. Iris tenax and I. innominata are the hardiest of the PCI species, and seeds with these species’ genes will be hardier than other PCI species for growing areas colder than WHZ 7. For wet climates, try Iris douglasiana, which is more moisture tolerant than other species. Iris munzii and I. hartwegii may be more heat hardy.
In hot summer areas, it is important to provide deeper shade, and to limit direct sunlight, keeping PCI shaded most of the day or in indirect light all day. Use mulches to keep soil and roots cool.
In hot summer areas of southern California, PCI are grown with shade, such as citrus trees; the trees are irrigated by flooding and PCI are watered at the same time. PCI flourish under these conditions despite daytime temperatures above 100 F. Regular irrigation is fine for PCI in hot climates; so long as the roots stay cool, the plants do well.
In hotter areas, growers at higher elevations are more successful than those at low elevations.
Adan, John K. 1974. Californicae in South Africa, SPCNI Almanac, Spring 1974, pp 4-5.
Jenkins, B. Charles. 1993. Letters: Scottsdale, AZ, SPCNI Almanac, Fall 1993, p 22.
Richards, Richard. 2002. Growing Pacific Coast Iris in southern California. SPCNI Almanac, Fall 2002, pp 6-7.
Ibid. 2007. The Pacific Coast Native Iris: To the most nearly equatorial (and most alkaline) extreme, La Mesa, California, SPCNI Almanac, Fall 2007, pp 11-12.
Ibid. 2009. Hardy older cultivars, SPCNI Almanac, Spring 2009, pp 13-15.
Weiler, John. 1984. Californicae in the Central Valley, SPCNI Almanac, Spring 1984, pp 4-5.
In cooler summer areas, PCI tolerate more sun. On the West Coast, the farther north PCI grow, the more sun they can take, up into southern British Columbia. These areas are very successful for PCI so long as soggy soils and frost pockets are avoided.
Kennedy, Helen. 1993. Letters: Surrey, BC. SPCNI Almanac, Fall 1993, pp 22-23.
Murray, Doug. 1994. Letters: Hope, BC. SPCNI Almanac, Spring 1994, pp 16-17.
Prothero, Joyce. 2005. Woodland companions: Heather and Pacific Coast Iris (Salt spring Island, BC), SPCNI Almanac, Spring 2005, p 17.
Schreiner, Ed and Linda. 2005. In the garden (Port Angeles, WA), SPCNI Almanac, Spring 2005, p 18.
In areas with wet summers, providing a drier microclimate is achieved by planting under trees with dense leaf canopies, or under a roofline along a building, sited to get some morning sun and otherwise be shaded.
Gardeners report success in the Midwest by starting plants from seed, and planting under overhanging roofs. This way they can control summer rainfall, sunlight, create patches of acidic soil, and improve drainage. They also suggest that growing varieties that are close to species, or species, provide more durable plants. Iris tenax and I. innominata are the hardiest of the species. I. douglasiana is not as hardy, but is more tolerant of moisture than most other species.
In colder winter zones, microclimates make all the difference. PCI have been successfully grown in zones 6, and occasionally zones 5 or 4, by ensuring they are protected from hard winter freezes and excessive moisture.
Bare, Garland. 1993. Letters: Lincoln, Nebraska, SPCNI Almanac, Fall 1993, p 23.
Fabel-Ward, Robert. 1987. Summer problems with Californicae seedlings in Arkansas, SPCNI Almanac, Spring 1987, p 6.
Ferrell, Bill. 1998. The winter of 1995-96, or whatever happened to my PCIs? SPCNI Almanac, Spring 1998, p 9.
Hulbert, Elaine. 1981. A Connecticut Experiment. SPCNI Almanac, Spring 1981, pp 4-5.
Schmieder, David. 2007. Letters: near Boston, MA. SPCNI Almanac, pp 9-10.
Ibid. 2008. Report from Eastern US Representative, SPCNI Almanac, pp 9-10.
White, John. 2007. Letters: Minot, MA. SPCNI Almanac, p 9.
Ward, Robert. 1993. How my garden grows (Little Rock, Arkansas), SPCNI Almanac, Fall 1993, p 21.
Generally, the higher one gardens above hot and humid climates at lower latitudes, the more successful. High elevation gardeners in California, Colorado, Mexico and Australia have reported success with PCI. Midday shade, frost protection, good drainage and acidic soil all contribute to their successes.
Adan, John K. 1974. Californicae in South Africa, SPCNI Almanac, Spring 1974, pp 4-5.
Jeffers, Dan. 1999. Growing PCIs in the Valley of Mexico. SPCNI Almanac, Fall 1999, p 7.
Keladis, Panayotis. 1990. Mile-high observations. SPCNI Almanac, Spring 1990, pp 14-15.
Grosvenor, Graeme. 2011. John Taylor’s experiences with growing and breeding Pacific Coast Native Iris in NSW, Australia. SPCNI Almanac, Spring 2011, pp 11-12, with photographs on page 2 and 19.
The one climate that PCI cannot tolerate is hot, wet, humid summers, typical of the southeastern United States. Sorry to say, if you live in an area with substantial summer rainfall, high humidity and high temperatures, you will have to postpone growing PCI until you move to higher latitudes, or higher and cooler elevations.
Members of SPCNI have tested this climatic barrier repeatedly. Some success has been reported from higher elevation gardens in the Carolinas, but farther south and at lower elevations, conditions appear to be too humid and hot for PCI survival. The references below are a small sampling of garden trials in hot, humid summer areas, or at higher elevations in otherwise hot, humid states.
Harrison, James. 2005. In the garden (Ashville, NC), SPCNI Almanac, p 16.
Schmieder, David. 2008. Report from Eastern US Representative, SPCNI Almanac, pp 9-10.
Some gardeners in colder climates (colder than WHZ 7 or 6) grow plants in containers for only a few years, replacing them regularly with younger plants from new fans, or seedlings.
This method has an important advantage: in areas with cold winters, the pots can be brought into a cool, well-ventilated greenhouse for the winter. Several growers in central and northern Europe have been successful with this method.
A number of nurseries and gardeners in California also use containers, because they can swap out plants in flower in display areas. Here, summer heat instead of winter cold is the issue. For more information, see Growing PCI in Containers.
Grisso, Ryan. 2005. Hybridizer’s corner, SPCNI Almanac, Spring 2005, p 15.
Tamberg, Tomas. 1988. Part 5: Overcoming obstacles, SPCNI Almanac, Spring 1988, pp 21-22.