Now is the time to plant or divide bearded iris. Bearded iris came from the Mediterranean area and once established have low water needs.
Iris (genus of the family Iridaceae) is a varied plant family with up to 300 species. Bearded iris is the crowning glory in the family. In Greek mythology the goddess of the rainbow was named Iris. Bearded iris (once commonly called flags) offer a rainbow of color for the garden with a variety of shades in yellow, orange, pink, wine red, blue, purple, white and almost black. There are even some varieties with brown or a tint of green.
Iris is available in various color combinations: two tones of the same color (bitone), light or medium standards with deeper contrasting falls (bicolor), a combination or two or more colors (blend), random splashes of color (broken color), stippled or stitched margin color (plicata), plus others.
Iris produce six-lobed flowers in multiple numbers on tall strong stems. The three upward pointing petals are called “standards.” The three downward drooping petals (sepals) are called “falls.” These falls expand from a narrow base into a broader expanded portion referred to as a “limb” or “blade.” In the center of the blade is the “beard" tuft of short upright extensions which are the plants filaments. Some iris have appendages extending from the beard that look like “spoons,” which are referred to as tongues. The bearded iris bulb is a rhizome.
Bearded iris is divided into types by size; dwarf varieties grow 3 to 11 inches tall; intermediate varieties reach 1 to 2 feet; while tall bearded iris grows 2 to 4 feet. Some classifications fall between these three types. Bloom time can be early, mid-season or late. All iris bloom in spring to early summer. Some varieties are “re-bloomers” with a second bloom time in early fall.
When planting iris consider the size and bloom time to allow for contrast and an extended bloom period. The size and bloom time is typically indicated on the plant (rhizome) when purchased.
Growing bearded iris: Bearded iris are typically planted in July, August and September and at least six weeks before the first freeze. In very hot weather planting in the later period is advised. Warm weather can also allow for planting in October or even November as long as there is sufficient time before any potential freeze to allow for root development. Iris can even be planted in the late spring when weather warms. However, there may not be a bloom that spring/summer. Sometimes newly planted iris need an extra year to become established in order to bloom. So don’t panic if you don’t get a bloom the first year.
Plants need well-drained soil and at least six hours of sunlight per day. If your soil is heavy or clay, add amendments (compost, humus, coarse sand) to improve water penetration. Creating raised beds or planting on a slope is another way to assure good drainage. Avoid using high nitrogen fertilizers. A low nitrogen fertilizer can be used after fall planting.
Plant iris so the tops of the rhizomes are slightly exposed, and the roots are spread out, facing downwards into the soil. Creating a small mound of soil in the center of a surrounding trench is a good way to plant the rhizome. In very hot areas a shallow cover of very loose soil, no more than 1 inch, can be used over the rhizome to prevent burning. Bearded iris needs room and good air circulation, so plant 16 to 18 inches apart (less for dwarf varieties). Do not mulch because mulching retains moisture. Too much moisture will cause soft rot of the rhizomes.
Once the iris is planted and the label removed, all iris plants look alike. Therefore, if you want to keep track of the variety name and color of each planted iris, make a chart of the iris planting location to refer to when the plants bloom. Or use a permanent garden marker next to the plant indicating variety name and color. These garden labels are available at many nurseries and garden supply stores.
Newly planted iris need moisture to encourage root growth; however, overwatering can encourage rot. After the new iris are planted, water immediately. Specific watering needs depends on your climate and soil. Deep watering at long intervals is better than more frequent watering. Once established iris may not need watering except during our hot summer weather or in arid areas. Over-watering is a common error and can lead to disease.
Divide large clumps of iris every 3-5 years. Carefully dig the clump out, taking care not to chop into the rhizomes more than necessary. Divide the rhizomes by pulling them apart with your hands. A good rhizome will be at least as thick as your thumb, have healthy roots, and have one or two leaf fans. Discard large old rhizomes with no leaf fans, dried out rhizomes, or smelly and mushy rhizomes. Wash off the soil to be able to check the rhizomes for pests or disease (rotting). Clip the leaf blades down to 4 to 6 inches to reduce stress on the plant and allow it to concentrate on growing new roots. Replant the rhizomes as described above.
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Reasons iris don’t bloom: Planting in too much shade. Using animal manure or high nitrogen fertilizer. Depending on soil type, no feeding at all can result in a starved iris that will not flower. Planting too deeply. Mulching which acts as a shade and retains too much moisture. Over or under watering.
Caring for iris beds: Keep beds free and clean of debris and weeds. Bloom stalks should be cut off at the base after all buds have finished blooming. Seed pods should not be allowed to develop. Healthy green leaves should be left undisturbed all summer. Diseased or brown leaves should be removed. Spent blooms on flower stalks can be carefully snapped off to keep blooming plants looking fresh and colorful.
Controlling disease or pests:
Rhizome Rot: Excessive moisture can lead to outbreaks of bacterial rot (smelly and/or mushy). Remove the rotting tissue as soon as possible by removing the soil from the rhizome and scooping out the mushy tissue, or completely dig up the plant to remove all of the rotten tissue. Drench the wound with a 10 percent bleach solution (1-part bleach to 9-parts water). Allow to dry for a few days before replanting.
Leaf spot: Brown circular spots on leaves caused by excessive moisture from irrigation and rainy humid weather. Cut off and destroy any leaf or part of a leaf that is infected. If this becomes a serious problem, spraying with a fungicide 6 weeks before bloom in the spring can be effective.
Slugs and snails: These pests cause streaks of eaten leaf parts. Control with hand picking in the early morning or with snail bait. Read the label to assure bait is not hazardous to mammals or birds.
Aphids, thrips and whiteflies: Insecticidal soaps can be an effective treatment. A variety of insecticides are available at garden centers, but use carefully to avoid harming beneficial insects (such as lady beetles that feed on aphids).
Companion planting: If you have an iris bed and want color beyond the iris bloom season, you can add companion plants to add interest and an extended bloom time. These can be other bulb type flowers that bloom with the iris and/or other flowering plants that have the same sun and low water requirements as the iris. Just make sure not to overcrowd or shade your iris.
Whether you want a specimen item, a full bed or a yard full of color, the rainbow colors of bearded iris won’t disappoint. You can check out the American Iris Society website (www.irises.org) and various suppliers online to tantalize your gardening appetite.
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For answers to all your home gardening questions, call the Master Gardeners in Tulare County at 852-3325. Tuesdays and Thursdays between 9:30 and 11:30 a.m.; or in Kings County at 852-2736, Thursdays only, 9:30-11:30 a.m.; or visit our website to search past articles, find links to UC gardening information, or to email us with your questions: http://ucanr.edu/sites/UC_Master_Gardeneers/