Irises are one of those flower families you either like quite a bit or not at all, perhaps unfairly. There are dozens of cultivars, so there’s bound to be something worth considering if you don’t currently grow them. If bearded iris aren’t your thing, the more demure beardless types might tempt you. Keep keep an open mind as we explore some possibilities.
Irises come in basically three types: Bearded, beardless, and dwarf, also called Dutch or netted iris, which are quite short and bloom very early, with the spring bulbs. You may be most familiar with the bearded type, which have been popular in this country since the 1800’s, especially in the 1920’s. But they have an even richer past. Here are a few highlights.
A Fascinating History
Irises are ancient flowers that date at least as far back as the Greeks and Egyptians. Iris are named for the Greek goddess, Iris, who was a messenger between the living and the dead. Iris flowers appear on the walls of Egyptian tombs, and irises have been associated with royalty throughout antiquity.
Later, the French designed their national symbol, the fleur-de-lis, based on the iris flower germanica florentina (and possibly the yellow water iris, pseudocorus, as well).
Then there is its use in perfumery. Curiously the scent is not derived from the flower. The root of the same fleur-de-lis iris, florentina, is called orris root and is a prized ingredient that has been used in perfumery for centuries. The root must be dried and aged for 2 – 4 years for the scent to properly develop, making it laborious and expensive. Some say orris root evokes the scent of violets. The soft powdery notes in the chypre perfumes Samsara and Shalimar originally came from orris root. (Now these fragrances are synthetically produced. Orris root is rarely used commercially in perfumery today.)
In modern times, iris have been heavily hybridized through a process known as tetraploid breeding, which doubles their chromesomes. The effect is larger flowers and many unusual color combinations. In my opinion, the results aren’t always lovely. The more extreme examples can be awkward and top-heavy. Many are stiffly upright with thick, brittle stems and clumped-together bud sets. But they do bloom longer, and with more buds per stem, than ever before.
Still, there are plenty of attractive cultivars in all colors, from soft pastels to bright golds and every shade of lavender to deep purple-black. Iris also comes in true blue, a rarity among flowers. There are even cultivars with striped foliage. Many iris are pleasantly fragrant.
Tall Bearded Iris
Bearded iris are named for contrasting fuzzy tufts, or beards, that grow between the standards or top petals, and the falls, the lower petals. Bearded iris need dry, sunny conditions with good fertility and superb drainage. They start blooming in April or May and continue through late June; a few even repeat bloom. (However, my repeater Eternal Bliss waits until November to bud up the second time, when invariably a hard frost ruins the encore.)
How to Use Iris
Irises of all types can be mixed with other perennials in any soil type and garden style, provided the rhizomes are kept exposed and their heads are in the sun. Growing 20″ to 48″ tall with stiff sword-shaped foliage, bearded iris add height and drama to borders, rock gardens, and along foundations.
Slender Siberian iris are especially well-suited for spots near pools, narrow beds and in rain gardens. All iris work well paired with medium shrubs and perennials such as peonies, yarrow, lilies, delphinium, foxgloves and the like throughout the landscape. A contrasting background such as evergreens, a wall or treeline help them stand out even more.
In short, nearly everyone has a spot for iris. They look best in small groups or massed. For instance, an island bed with a mix of small conifers and iris makes an eye-catching focal point.
I find many of the bicolors too garish, but I do like to group several similar tones together or adjacent. A large bed of mixed iris is also very lovely.
Siberian Iris
Siberians are beardless and have a daintier form than bearded iris, with grassier foliage. They make excellent landscape accents. Solid blues, purples, whites and yellows make up the bulk of selections, along with a few veined varieties such as Shaker’s Prayer.
There are numerous hybrid Siberians on the market in all sorts of color combinations now. Unfortunately I find many of them to be rather strange, with unnatural shapes in bizarre shades. But that’s just me. Do check them out. You never know when a particular cultivar will strike your fancy.
One choice I can definitely vouch for is Caesar’s Brother, a tall and hardy solid purple that’s proven its value over the years. The color is so dark it’s hard to reproduce accurately. It blooms reliably year after year, even with benign neglect. Pair it with lighter toned companions for a lovely color statement.
There are a number of light blue and yellow Siberian irises as well. Some will even naturalize, slowly spreading to form small colonies over time. But most don’t spread much and are easily managed.
Siberian iris prefer moist, even wet, feet. They are excellent choices for alongside ponds, streamsides, and wet meadows (but not in standing water). Most do just fine in regular garden soil as long as they aren’t allowed to dry out for prolonged periods. Their smaller blooms make them perfect for rain gardens, flowerbeds inundated by downspout runoff, or anywhere that regularly gets plenty of water.
I don’t have any direct experience with Dutch iris or Japanese forms, so I won’t be covering them here. But if you love iris, check them out. Some of the petite forms are very sweet.
General Care
As noted above, bearded iris prefer neutral soil in sunny, dry conditions, while Siberians like it wet and on the acidic side. Siberian iris can also tolerate a bit of dappled shade. Both are shallow-rooted and grow from rhizomes (a form of swollen stem) which for bearded iris, resemble fingerling potatoes.
Iris are quite easy to grow, but one down side is their susceptibility to fungal leaf spot, crown rot and borers. The best defense is to keep the rhizome tops exposed, provide excellent drainage, remove dead foliage regularly and divide crowded plants to maximize air circulation.
Planting Bearded Iris
Unless they are in nursery pots, most iris are sold “bareroot” as dormant rhizomes. They will already have their tops trimmed. They should be planted as soon as possible after you get them, ideally in July or August.
For actively growing iris that need dividing, cut off the top foliage (called the fan) to within 4 inches of the base. This step will stimulate root production instead of top growth and accelerate establishment. Dig up the rhizome and gently pull apart the roots with your fingers to separate them. Clean up divided plants before replanting, cutting away soft, mushy or dead tissue. If you wish, wash them with a 10% bleach solution if they had soft areas cut away, and leave them to dry for a day before proceeding. Or proceed directly if they seem healthy.
Gently cultivate the soil where the iris will be planted. Ensure it is free-draining with at least 6 hours of sun a day. A southern exposure is great if you have it. Add organic matter if the soil quality is poor. Slightly acidic to neutral ph is ideal. Fortunately iris do just fine in amended clay or sandy soils.
Place the rhizome horizontally on the ground, making a little mound under it, with the top (fan) facing up and roots splayed out to the sides and downward. Cover roots with soil and firm in well. The rhizome itself should be no more than half-buried, with the top visible at all times. If it becomes covered later on, just clear it off from time to time. This step is very important in helping your iris fend off borers and for healthy flower production.
Space bearded iris about 12 inches apart in groups of 3 to 5 rhizomes or more. (Closer spacing will look good immediately, but keep in mind they will need dividing soon if you go this route.) Water frequently at first until you see new growth, then stop watering and allow to establish. A light mulch of pea gravel or sand is helpful in suppressing weeds while discouraging fungal rot.
Newly planted iris will display good fan production by fall. Do not cut off the fans until they naturally start to go dormant from frost, usually in late November here. It’s a myth that fans need cutting earlier.
New iris should bloom modestly the first spring after they’re planted, easily doubling in size and number of blooms by the second year. Check for crowding thereafter; most iris need dividing every 3 to 5 years to keep them vigorous and healthy. Fertilize lightly each spring with a good general granular fertilizer that’s not too high in nitrogen (I like Espoma Flower-tone) and again after flowering. Mulch sparingly, or better yet, use gravel or sand.
Diseases and Pests
Wet humid conditions encourage various fungal diseases, which show up as rusty markings or white-ringed spots on the foliage. Remove affected leaves or cut away the damage to slow down the advance. Clean your tools with a 10% bleach solution to avoid spreading the rot to unaffected plants. Fungal leaf spots are unsightly but not the end of the world. Sometimes simply trimming off the brown tips and pulling off a few leaves is a big help.
For more serious cases, cut off and trash all affected leaves and dead matter; spray with either a commercially formulated antifungal treatment for iris as directed, or use a home remedy that raises the ph level (see tip below). If necessary, dig, clean and divide affected plants. Replace the soil to a depth of six inches, then replant the cleaned and trimmed fans. Make sure they have excellent air circulation and keep weeded.
TIP: Homemade antifungal spray — Add two teaspoons of baking soda and a half-teaspoon of mild dish soap into a one-quart spray bottle and fill with water. Shake. Spray all iris leaves, both affected and unaffected, thoroughly with this solution. Repeat once a week for four to six weeks.
Borers are another story; their larvae are destructive and can kill iris. The borer adult is a brown, night-flying moth. It lays eggs in the fall on dead and dying foliage; the eggs hatch in spring and the pinkish larvae tunnel into the new growth first, eventually moving into the rhizome, where the 2-inch caterpillars chew tunnels and cause major bacterial rot. Check your irises in spring through July to look for signs of borers, such as water-soaked leaves, abnormally dying foliage and mushy rhizomes.
The best treatment is immediate manual removal, and practicing good garden hygiene. Dig up the afflicted iris, scoop away any mushy rhizome tissue with an old spoon, and destroy all affected foliage. Drench the whole thing with 10% bleach solution (1 part bleach to 10 parts water) and allow to dry thoroughtly; then replant the trimmed and disinfected remainder in a new location.
Commercial pesticides designed to kill borer larvae can be applied in early spring; if you wish to use such a pesticide, do your homework as to which one to use, and follow directions carefully.
If you experience rot or borers, don’t despair; you’re not alone. Most iris gardeners have to deal with these problems at some point. Fortunately, most treated iris rebound just fine if caught early enough, going on to recover and provide years more pleasure.
Planting Siberian Iris
Siberians prefer rich, damp, acidic soil. Soak the rhizomes in water for several hours or overnight prior to planting. Add humus or peat moss to acidify the soil, or a product like Holly-tone, if necessary. (Do not plant Siberian iris in standing water. Use iris specifically grown for ponds, which is a different species and not covered here.)
Siberians should be planted more deeply than bearded iris. Cover the rhizomes completely with 2 inches of soil. Space two feet apart, as they will develop into sizable clumps over time. Siberians can handle less frequent dividing, but if flowering and vigor wane after some years, divide them to reinvigorate.
While borers and fungal rots can affect Siberian iris too, they tend to be less prone to diseases and pests overall. Many people prefer Siberian iris because they tend to need less care. It should be noted that their bloom time is more fleeting than the beardeds, so enjoy them as soon as they flower.
Of course, my experience with iris is only one gardener’s account, and a rather limited one at that. But I must say I’ve come to value mine for the color and substance they add in late spring. I do hope you will give iris a second look, and perhaps add a few new ones this year.
