September 20, 2015
Many irises are easy to transplant at any time of year. Dig them up, divide, cart to new homes and tuck in. Clip off some leaves to reduce moisture loss while the new roots form, and away they go. Not so for PCIs. Treat them this way, and they go root tips up before you can find your watering can.
|Healthy PCI transplants: new fans, and healthy new white roots. Both of these I. douglasiana pieces are ready to plant.|
There are two times of year to successfully transplant PCIs: Autumn and Spring.
At these times, PCI roots are in active growth. Check the roots, removing soil gently around the base of a fan or two. If there are white roots, one to four inches long, then get out the shovel and start digging. It's time.
|New fans on a PCI, but no new roots yet; this plant needs to wait a few weeks before being divided.|
Why Autumn and Spring for root growth? Pacifica Iris are native to the West Coast of North America, which has a Mediterranean climate––during the drought period each summer, these and other native species go dormant. In mild winter climates, PCI may have live roots all winter, but they dry down and wait out dry summers.
Summer drought duration depends on latitude, the farther south you are, the longer the duration, which varies from less than three months to more than ten months on the West Coast. I garden at 46°N, so droughts usually last less than three months, though this year it was more than five.
If you water regularly, PCI initiate new roots earlier in the fall than do those depending on rain. You can divide and transplant much earlier in the fall and later in the spring.
|This flat of PCI seedlings has been watered regularly all summer, and is ready to move into the garden.|
PCI seedlings in pots are tough, and can stand being transplanted several times in the first year or two of life. Even larger plants, one to five gallons, can withstand transplanting slightly outside the Autumn or Spring periods. These have all had regular water, as they must to live in pots.
Mulch after planting to keep roots cool
Amend soil with carbon, such as compost and biochar
Move plants on cool cloudy damp days rather than on hot sunny days
Add 'Superthrive' (a registered vitamin formula for plants) to the watering can
Water well for a few weeks after planting
Use a dilute liquid fertilizer when watering
Every Autumn I host a 'Come and Dig PCI' day in my garden, to share out plants to other gardens in my community. I checked my plants this week; new fans are starting to form, and new roots are short. I'll wait a week or two, until new roots are more than an inch long.
There are exceptions; one variety has long white roots and could be divided now, but it will tolerate moving in a few weeks. The seedling PCI can be planted anytime from now until early November. They are much tougher than fan sections, which is why growing PCI from seed is so successful for many gardeners. Society for Pacific Coast Native Iris will hold its seed exchange from 1 November to the end of the year, so now is the time to be thinking about what species and hybrids you'd like to grow in your garden from seed.
|New white roots, this PCI is ready for a new home.|
For western gardeners, Autumn is the best time to plant many native plants, not just Pacifica Iris. Trees, shrubs, perennials, ferns and grasses all do well if planted now (late September to early November), as the weather cools and moisture arrives from the Pacific Ocean over western North America. This gives the plants a jump on growth for the coming year by establishing good root systems first, with much less water use now and in coming years.