Irises are showy flowers in the garden. They are easy to care for and easily multiply giving you many more plants than you started out with, and quickly. They are beloved by many gardeners for their old-fashioned charm, and are gaining respect with younger gardeners because of their low maintenance .
When mentioning irises in the garden, however, many people automatically think of the bearded iris, or German bearded iris. But, there are actually several different kinds of iris, and how they grow, how to maintain them, and when they bloom are completely different depending upon which type of iris you have.
There are two broad types of irises: those with bulbs, and those with rhizomes. Within these two categories, several more types, or species, exist. While the following diagram is not an exhaustive list, it does cover the main species of iris for garden cultivation. There are approximately 300 species of iris. Garden cultivation classification differs from taxonomical classification.
Let’s first examine the underground ‘Stem’. Where irises are concerned, this is the first question you’ll want to ask yourself when identifying them in the garden.
Rhizomatous iris
A rhizome is a fleshy, underground ‘stem’, or root, acting similarly to a bulb. The rhizome stores food and energy for the iris through difficult seasons, be it winter in the east coast, or drought on the west coast.
Often, you can see the rhizome partially out of the soil. They don’t generally like to be planted too deeply.
If you don’t see the rhizome at the base of the plant, you may need to dig up one of the stems to find the underground terminus to see if it is a bulb or a rhizome.
Once you have determined that there is a rhizome, the next step is to look at the petals. All iris have two types of petals; those going upward, known as the ‘standards’, and those going downward, known as the ‘falls’. Every iris will have three of each.
If the falls, or the downward petals, have a ‘fuzzy’ looking section right at the center, you are looking at the beard. This is your bearded iris. A majority of rhizomatous iris will have beards. A beard is usually quite distinct – often a different color from the petal. If you touch it you can feel the soft, hair-like bristles of the beard.
Sometimes there is a color patch but no beard. This is not a bearded iris! This is much more common on bulb iris, but if there is no beard on a rhizome iris, they are called, as expected, a beardless iris. The most common beardless iris is the Siberian iris, which like its cousin the bearded iris, is extremely versatile.
The last type of rhizomatous Iris is the crested iris, which is a native North American iris found in woodland areas and is becoming more commonly cultivated in gardens. Of the 28 native iris found across the United States, 2 of them are crested.
Rhizomatous iris, both bearded and beardless, are super hardy in the garden. The rhizome stays in the soil storing energy and allowing the plant to withstand excessive heat, drought, cold, and even competition and predation. Once established they generally do not need any supplemental summer watering, even in dry and hot California. They are a good choice for areas without irrigation, outside deer fencing, areas with gophers, around compost piles and around chicken coops. However, they will do fine if in an irrigated garden, too.
Bulbous Iris
The second broad category of iris is the bulbous iris, or that which grows from a bulb. Again, as with the rhizomatous iris, the best bet is to dig up one of the iris to inspect its underground stem to see if it is a bulb or a rhizome.
Iris bulbs are very small, much smaller than a daffodil or a tulip bulb. They are about the size of a crocosmia corm but rounder.
Bulb iris will never have beards. There are two main types of bulb irises in the garden – the Dutch iris and reticulata iris. Reticulata iris will bloom much earlier than other iris. You will find them coming out in February along with your earliest spring bulbs. Dutch iris tend to bloom at the same time as rhizomatous iris, which is, after the daffodils and tulips have finished their show.
Bulb iris are planted in the fall, like almost all other bulbs, and the same time as daffodils and tulips. Deadheading prolongs bloom time. Dutch iris will double every year, giving your large masses of bulbs if not divided.
Do not cut down the leaves after the iris has bloomed. Thin the bulbs only after the green leaves have completely faded. The leaves capture energy through photosynthesis and carry it to the bulb for the following year. Bulb irises in the garden do not need a lot of water through the hot summer. However, they do perform better if they either have once monthly watering, or alternately, the base of the plant is shaded.
Because iris bulbs are small, they can be pushed by underground rodents to other areas of your garden. If you see a Dutch iris way across the garden where you did not plant it, that’s usually a sign that you have moles or gophers.
