Pacific Coast IrisAn Introduction
Irises for most people are the tall bearded varieties flowering late May into June. Easily grown and colourful but short season and not easily mixed with other perennials.
There is a huge range of other types of iris, less widely grown but with different characteristics, from pond to desert there is an iris that will be happy in your garden.
Pacific Coast Irises are among the least well known group within the UK, which is a pity as they are amongst the most beautiful, and are easily grown here, as long as their needs are understood. The reason for their rarity is that their growing needs do not fit in well with the production and marketing requirements of the nursery trade. Once settled in the garden they are fine, it is getting them there that has been the problem. But I am getting ahead of myself.
PCIs are in the beardless iris group, along with siberians, water irises, our common flag iris, and a huge range of others. As the name suggests they are native to the Pacific coast of North America, from Canada to Los Angeles, but generally not too far inland. There are several species in the group and these will all cross with each other, so you do not often see any of the pure species grown in the UK. Of those that are the two most commonly encountered in the UK are Iris douglasiana and Iris innominata.
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| Iris innominata. |
How to grow PCIs
I can only speak from my own experiences in the east of England, in other parts of the country, or in other countries the different climate may mean different cultural techniques may be required.
The two most important factors are good drainage and non disturbance.
The rainfall in their natural habitat is about the same as where I garden, but occurs mostly in winter, with nearly none in summer, when the plants go dormant. They retain their foliage but do not grow. Winter wet does not seem to bother PCIs much in my garden, but summer wet, when they are dormant, may lead to rotting unless the drainage is good. Again, in nature they grow under trees which dries the soil in summer even more. In the wetter parts of the UK planting under trees is reputed to be the best way to grow them, but they will flower better with a bit of sun. In hotter climates part shade is recommended. In the baking summer of 2022 PCIs were totally happy, which is more than I can say for my Siberian Irises.
Disturbance should be avoided for as long as possible. Unlike bearded iris they do not need to be split on a regular basis, the clumps just get bigger, and with more flowers each year. They should go at least six years or more before it becomes necessary. If you do have to split or move PCIs the best time is when they are starting to grow after their summer dormancy, about October for me. The worst time is when they are dormant, which usually results in certain death of the plant. Springtime, up to March, maybe April at a push, is Ok, especially if you are planting a potted new plant. (I have not had good results with purchased bare root plants, at any time of year,)
One exception to this seems to be seedings, up to maybe a year old, which seem reasonably happy to be moved at any time. If splitting a plant, do so in big pieces, at least three fans, and do not let the roots become dry.
I have not read a good reason why PCIs are fussy in this regard, but my speculations, for what they are worth, are that PCIs develop roots that last many years, and go deep. Bearded iris, as a comparison, grow a new set every year, and last year's roots die naturally. You cannot save the old roots of PCIs once you have disturbed them, so you have to transplant at a time when new roots are naturally being produced, ie the autumn, and even so the plants will undergo a setback so are best left undisturbed if possible.
Soil type.
This is another area where my experiences are at odds with the accepted wisdom. Apart from good drainage it does not seem to matter for me what the soil type is. Neutral to acid is generally recommended, but my soil is derived from chalk and clay. I admit I do not garden directly on the chalk strata which line the valley tops around me, but my soil is derived from it and the underlying clay, courtesy of the ice age glaciers and later erosion. Only one PCI variety that I grow really does not seem to like it, (Pinewood Sunshine if you are wondering), and the varieties right next to it seem fine. I intend to move this variety in the next week or so, to see if it is happier in another part of the garden.
PCIs like to be mulched, pine needles are recommended but are not available to me, so garden compost has to do, which seems to be acceptable.
Full sun is best, though some shade is OK, more than a bearded iris would like. Competition from neighbouring plants is tolerated to a degree, so PCIs fit in better in a mixed planting than beardeds do.
Hardiness
All the varieties I grow seem quite hardy if planted in the ground. Those I had in pots did not appreciate having their roots frozen solid for a week last winter, but most survived, if only just.
Some American species are reputedly tender, but I suspect that there are none of these grown in the UK.
Diseases
PCIs seem quite pest and disease free, as long as they do not rot from being too wet that is.
Other problems?
The main issue with growing PCIs is obtaining them in the first place. There are very few nurseries offering them. This is a pity as the UK was once a leading country in the breeding, registering and distributing of PCIs, sadly no longer. Obtaining stock from abroad is now impossible for all intents and purposes. Avondale Nursery near Coventry is the best source I have found. Or you could grow them from seed...? (it's easy)
Seed.
The best source of seed is a seed exchange from a gardening society or the British Iris Society. Some of the best and most beautiful varieties that I grow are plants raised from seed exchange seed. For the more adventurous there is always the American Society for Pacific Coast Native Iris.
Of all the types of Iris that I have tried to grow from seed, Pacific Coast Iris are the easiest (and fastest).
Planted outside in pots in the autumn good germination can be expected in six to eight weeks. No cold treatment or soaking is needed. After germination I keep the pot in a cold greenhouse overwinter, to protect the small seedlings from the worst of the weather. I plant out in a nursery bed or a bigger pot in early spring. You may get some losses at this stage, this seems normal. You may get a first flower eighteen months after autumn sowing, but certainly in the following year. Spring sowing is also fine, but keep the seedlings moist for the first summer. Seedlings do not seem to show summer dormancy in their first year.
Ideal germinating temperatures are between 15 and 20 centigrade. Hotter temperatures stop germination. I use ericaceous compost For PCIs in pots at all stages.
I hope all this helps. It is based on my personal experiences. You may find that different ways may suit you better, do not hesitate to experiment. The important thing is to try, you may be pleasantly surprised, or perhaps not, but you will never know unless you have a go.
Happy Gardening
Rob.
