Check roots to know when to transplant Pacifica Iris

February 26, 2017 

Kathleen Sayce

The West Coast is having a winter of pronounced weather, if one thinks of a series of Atmospheric Rivers (AR) as ‘pronounced’. I know I do—no soft drizzling days here, no ma'am. ARs are firehoses in the sky, huge rivers of moisture that deliver strong winds and warm rains from the Equator to higher latitudes. 

Above latitude 46 on the ocean, where I garden, rainfall is well above average for the water year, which began October 1st. Other areas are also above, including much of California, which is experiencing a definite wet season in an otherwise years-long drought. Those warm storms alternate with days of clear skies, balmy temperatures, and weeks of more typical winter weather, including snow, hail and much colder rain. 

Pacifica Iris clump with a little hail topdressing:  yes, this plant has active root growth below ground. 

This seesawing back and forth leads me to wonder what is going on below ground and when will be a good time to transplant irises, including Pacifica Iris. There is only one time to transplant them, and that is when plants are in active root growth. 

Healthy PCI buds suggest it's time to divide and replant--but check the roots first to ensure success. 

This means you have to gently scrape out the soil under the new buds and check the roots. Normally this is in the fall after rains begin, following dry summers, or winter into spring, before the annual summer drought begins. 

PCI 'Mission Santa Cruz' has a lovely new root, and is ready to be moved. 

Another general rule is that while Pacifica Iris are flowering and ripening seeds, they can be transplanted. I’d like to know how widely this works, so if you have experience with transplanting during spring, please let me know, or add a comment here at the bottom. 

If you live in other climate areas and grow Pacifica Iris, begin by checking roots on the plants you want to divide, repot or transplant.

Between hail storms today I went out and dug around a few plants to see what they are doing in the soil. I found a mixed bag, ranging from completely dormant (Iris tenax) to starting to grow (several recent Ghio hybrids). 

This PCI fan shows the roots from young (and active) on the left through the full sequence of older darker roots to fine roots off the rhizome on the right. It's ready to be replanted. 

I’ve mentioned before that hybrids from the Bay Area in California flower too early in my garden to escape heavy rain, and thus rarely set seed. If the rain is so hard that flowers are battered, bees aren’t flying around either.  These irises also begin growing very early—perhaps they are more attuned to day length than temperature. 

The finding in late February in my garden was that some new roots are starting to elongate just behind the new fans in some plants. There aren’t very many yet, one root per fan so far, where there will be four or more in a few weeks, but that’s enough of a sign of new growth that those early flowering hybrids can be dug up, divided, and replanted. 

Iris tenax is just starting to break winter dormancy; you can see the green shoots to the upper right. Roots are still brown. 

I will wait a few weeks for the others. Iris tenax, I. thompsonii, I. innominata and their various hybrids are still largely dormant, with few signs of new leaves on the first, and only a few new shoots on the latter.

Iris lazica has a bud. Not a PCI, but a good companion to them, and one that adds months of flowers to the garden, as does I. unguicularis. 

For comparison, in southern California, PCI are in active growth and starting to flower. Meanwhile, Iris lazica has put up a first bud, along with PCI ‘Premontion of Spring’, which has been flowering off and on since last September, as has Iris unguicularis. 

The next time you look at your Pacific Iris plants and wonder about getting starting dividing, go check the roots first. It’s the best way to ensure success. 

Autumn: Transplanting time for Pacifica Iris

Kathleen Sayce 

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.

Other tips:

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.