Iris unguicularis is still often found listed erroneously as Iris stylosa. Many people grow it but it is not often offered in the trade. I. unguicularis is one of the gems of the genus iris because of it's bloom time. It often starts to bloom in October and blooms through March or even into April. When the temperature dips into the single digit range the flowers and buds will all freeze solid then turn to mush when they thaw. However within a week, if the weather warms above freezing, the plant will send up more buds and again be in full bloom.Like many other species, taxonomists cannot agree on the status of the different forms of I. unguicularis. To us as gardeners it really doesn't matter as long as we know there are three very distinct types of plants in the unguicularis group.
Iris unguicularis itself is quite variable. The leaves range from 1/4" to 1/2" in width and are generally about 15" long. They are sometimes ribbed and may vary from a bright green color to almost grey blue. The leaves are very tough and as a general rule the narrower leafed forms are more bluish and leathery while the wider leafed forms are more green and succulent. The flowers on I. unguicularis are mostly in shades of lavender but vary from pure white to deep purple and there is even a clear pink form. In the typical form the standards are lavender with brownish spotted hafts. The falls are lavender with a large white area on the upper part that is heavily striped with lavender. There is also a yellow signal stripe on the falls. The flowers are sweetly scented and though they do not have a stem they have a very long perianth tube so they can be used for cut flowers. Since they have almost no stem if you are looking for seed you must search among the leaf bases almost underground to find the pods.
Iris unguicularis is a plant of the dry Mediterranean climate. It is a bit tender and resents heavy frost. I have grown it in a protected spot out doors for about ten years. One year when the temperature dropped to 0° F. the foliage was completely burned to the ground, but later it again started to bloom and in the spring grew new foliage. The whole freezing episode did not really harm the plant, only made it unsightly for a while. I. unguicularis requires a good baking in the hot summer sun. In the Puget Sound area the usual suggestion is to plant I. unguicularis against your foundation on the south side of the house. It will then get very hot in the summer and stay quite dry and will also get a bit of lime leaching from the concrete foundation to provide the neutral to slightly alkaline soil it prefers. Do not let I. unguicularis dry out completely, it needs a bit of dampness under ground within reach of it's roots. I water once or twice during the summer if we have no rain but never when the sun is on the plants. Iris unguicularis does not seem to need a lot of fertilizer. A light application of 5-10-10 in the fall and again in the spring after bloom is all it will need. The biggest problem you will encounter is slugs, they love having flower salad in the middle of winter. You may never see the flowers of I. unguicularis unless you are diligent about baiting for slugs. It is well worth a little effort to have iris in bloom all winter.
There are several named clones of I. unguicularis to be found in collectors gardens. 'Mary Barnard' is one of the best in a dark reddish purple. It is a very strong grower that always looks like it will bloom itself to death. 'Walter Butt' is just the opposite, neither growing very well or blooming heavily but it's very large pale silver orchid flowers make it worth the effort to give it a little extra care. There is a pure white form known as 'Alba' which has given rise to some white seedlings. 'Alba' and all it's seedlings being fairly narrow in form. There are several pink forms the most commonly encountered being 'Starkers Pink' which also is a rather weak grower. There are more and better forms but most have not been imported into this country. The field is wide open to a hybridizer with a bit of creativity.
Iris cretensis is considered by some to be a separate species and by others to be a small variety of I. unguicularis. It is a tiny plant found on Crete as the name implies. The leaves are only about 1/8" wide and about 6" to 7" long. The tiny flowers which bloom from January to April are in proportion to the leaves. The blade of the fall is almost entirely covered by the purple and white striped area with only the tip of the blade being a solid color. The signal stripe on the fall is orange and the standards are lavender. This tiny plant is not easy to grow or flower as it seems to be more tender than it's larger relations. It probably does not get enough heat in the Puget Sound area to bloom well. I cretensis also seems to need a more alkaline soil than the larger I. unguicularis. There is a pure white form of I. cretensis which is truly a collectors item.
Iris lazica is the third member of this group. This is a very large robust plant with leaves up to 1" wide and 20" or more long. The flowers are very similar to the typical Algerian form of I. unguicularis. I have not heard of any other color forms of Iris lazica. This plant comes from the area around the Black Sea and is much more content in our climate. It will even tolerate some shade although I grow and bloom it well in the same bed with all the other forms of I. unguicularis. I. lazica blooms later than I. unguicularis, not starting into bloom until January or February and blooming through April. Brian Matthew states that he has never seen a form of I. lazica with a stem but has heard that it sometimes has a stem. The form I am growing has a 6" stem that is sometimes even branched but has a much shorter perianth tube. I. lazica does not have the sweet scent that I. unguicularis has.
All of the plants in this group are well worth growing. Some are more showy than others but their bloom period makes all of them desirable. I would hope that they will all become more available in the trade. The KCIS beardless sale usually has some of them to offer. The only other sources of Iris unguicularis are the seed exchanges such as the SIGNA exchange.