Plant into a one gallon or larger pot, using a good planting mix. I use Supersoil, available at your local gardening or home improvement store. Perlite can be added with good effect. Keep the pot moist but not soaked until planting into the garden, usually in the last two weeks of February. New growth ought to be showing. It can be done a bit earlier or later.
Pots can be held over the summer in a shady spot. Do not allow the pot to dry out, but do not keep it soaked. I water my potted PCIs twice a week in summer and more often if it gets really hot. If the PCIs are held in pots over the summer, then plant when the weather cools. Mid-November is a good time. New roots have started growth by that time.
Protect the root ball by keeping it as intact as possible when planting from a pot into the ground.
Planting the rhizome while it is in bloom in the spring is an invitation for the plant to attend the annual PCI suicide conference.
If you buy a plant in bloom in a pot from the nursery, it is best to hold it over the summer according to the suggestions above. Do not believe the people at the plant nursery when they say it can be planted any old time. Of course it can be planted any old time, but you will have to replace it with a live plant next year.
Adequate soil preparation pays off. The more care you take, the more thriving plants you will have. If you don't have sandy soil, add gypsum, as heavily as one pound per square foot.
If you don't have incredibly rich soil, add peat moss at the rate of as high as one cubic foot of peat for every twenty-five square feet of soil area.
If you don't have neutral or acidic soil, a very rare condition in Southern California, add soil sulfur at the rate that will make your soil netural or slightly acidic. If you can measure your acidity, fine. If you cannot, then use a pound per ten to fifteen square feet of soil area.
Mix the ingredients in, then plant your PCI rhizomes. Water thoroughly and keep the bed moist for several months. Depending on the rain in Southern California is like depending on the California legislature to pass a budget on time. It almost never happens.
Plant PCI's in moderate or dappled shade. Too much sun drives the soil temperatures up and PCIs are susceptible to heat and moisture in summer. Too much shade will inhibit bloom, and the foliage is not attractive enough on most varieties to justify growing them for that alone. When in doubt, err on the side of too much shade.
Water in the summer or during our periodic and predictable dry spells at other times of the year. Water every week to ten days, depending on how fast your soil dries out. Established clumps can take considerable drought but newly planted rhizomes cannot.
Relax. You cannot possibly come close to killing as many PCIs as I have during my long and lethal career growing PCIs. The beauty of the flowers justifies the care the plant requires.
For more information about PCIs, please visit the Society for Pacific Coast Native Irises website.