suburban life magazine, may 1908

F.A.Q.

Frequently Asked Questions
about iris cultivation


Compiled by Laurie Frazer, MN



Why are my bearded irises not blooming?
Why did my iris change color?
How do I prepare irises for shipping?


I have no bloom on my bearded irises. Why are they not blooming?

Here are a few reasons why bearded irises may not bloom:
  • Not adequately established -
    Some iris cultivars need a year or more to fully establish in their new locations before blooming. If you relocate them frequently, they may never become well enough established to bloom. Plant irises far enough apart to allow for several years growth before requiring division.

  • Inadequate sun -
    Bearded irises need at least 6 hrs of direct sun a day to bloom well.

  • Nutrient deficiencies -
    Consider having a soil test run to make sure your soil provides all necessary plant nutrients in appropriate amounts and fertilize according to the recommendations returned with the soil analysis. Soil that has been growing irises for many years without amendments or fertilization is probably nutritionally depleted. Avoid high-nitrogen fertilizers. If bearded irises are fed high-nitrogen fertilizers, they may grow lush foliage with little or no bloom.

  • Inappropriate watering -
    Bearded irises might not bloom well if they experience periods of extended drought, though the plants themselves are quite drought-tolerant. Conversely, bearded irises that are overwatered are often susceptible to bacterial soft rot and fungal leaf spot infections. If you provide supplemental water, water deeply no more than once a week. Soaker hoses are preferable to overhead watering to avoid spreading leaf diseases from plant to plant.

  • Planted too deeply -
    Bearded iris rhizomes should be planted so the tops of the rhizomes are at or slightly below the soil surface. If planted too deeply, bearded irises will grow leaves but may not flower. Be careful, also, not to allow mulch to cover the rhizomes. Make sure any mulch is pushed away from the rhizomes.

  • Overcrowding -
    Overcrowded clumps often quit blooming until they are divided, OR irises closely planted with other plants may not bloom well (or at all) if they are struggling to compete for sunlight, water, and soil nutrients.

  • Weeds -
    There are certain weeds and grasses that are so aggressive they can inhibit the performance or even survival of plants they invade (Canada thistle being one of them). Keep the weeds and grasses away from your irises.

  • Ill health -
    Irises that are diseased or under insect attack may not be able to bloom until the problem is eliminated.

  • Late freezes -
    Killing freezes that are severe enough to damage iris foliage within six to eight weeks prior to normal bloom can abort developing stalks even if the stalks are not yet showing above the foliage.

  • Immature rhizome -
    Rhizomes will not bloom until they are mature. If you have planted smaller rzs, you probably need only wait for them to grow a bit before they'll bloom.

  • Irregular bloomer -
    All irises are not created equal. While some irises may bloom very regularly in your garden once established, others may never do any better than blooming once every several years ... or perhaps never blooming at all. The same cultivars that bloom beautifully and reliably for a neighbor down the road or a friend across the country may do nothing more than sulk in your own garden. The only way to discover which irises will perform best for you is to keep trying different cultivars, growing them properly, and replacing those that don't meet expectations within 2-3 years after planting.

My purple iris turned white! Why did my irises change color?
    Irises do not normally change color - not on a permanent basis, anyway. It is possible that herbicide drift can cause temporary changes in iris pigmentation (do you use RoundUp or have a nearby neighbor who does?). If that is what happened to your irises, they will probably return to normal color next year, assuming they are not subjected to herbicide again. I don't believe there are any nutritional factors that can completely change an iris's color pigment, though growing conditions can certainly influence color saturation. It wouldn't hurt to have your soil analyzed for any possible nutrient deficiencies. The amount of available sunlight and ambient temperature can also influence color intensity to some degree, though not to the point of turning one color into an entirely different one i.e. purple irises turning white.

    There are, however, other possible explanations for these apparent flower color changes:

  • Irises often do not bloom every year. It is possible that your dark colored irises neglected to bloom this year, while lighter ones (perhaps left by a previous owner) within the same planting area did bloom.

  • If you dug your original irises from a bed where only purple irises were blooming, perhaps you assumed that you dug only purple irises. However, there may have been a number of other colors of irises in the original bed that weren't blooming at the time you dug but that did bloom later in your own garden.

  • If you dug and replanted a bed within the last several years, it's possible a tiny piece or pieces of a previous iris planting remained in the bed and has now matured to blooming size.

  • An animal or child may have uprooted a rhizome from elsewhere and dropped it into your garden without your knowledge, or a neighbor may have tossed unwanted rhizomes over the fence into your yard where they took root. It happens.

  • Certain cultivars are far more vigorous growers than others, and in closely planted beds, the more vigorous growers will almost inevitably choke out the less aggressive irises over time.

  • Your original irises may have been bee-pollinated within the last few years. The seeds from those crosses may have ripened, dropped, and germinated among the original plants, and now you have a bunch of new seedlings blooming within your original clumps. Iris seed does not grow true to the parent plant and may well have produced some new colors in your iris bed.

  • On extremely rare occasions an iris may "sport", meaning the iris may produce an offset that differs noticeably in appearance from the original plant. HONORABILE is one well-known example of a cultivar that has produced several sports in its long history. The sport offsets, however, do not change the color or appearance of the original plant.

  • The only way to get all of this sorted out is to place a tag around each bloomstalk to identify its color, then dig and divide all of the rhizomes 6-8 weeks after bloom, replanting each color separately about 2' apart so they won't crowd each other too soon. Remove any seed pods that may form before they have a chance to ripen to avoid a repeat of this problem in your garden.

How should I prepare iris for shipping?
    The procedure for preparing iris plants for shipment from one garden to another varies according to the iris variety being shipped. There are essentially four basic categories of irises: bearded (bearded species and cultivars, arils, and arilbreds), crested (cristata, tectorum, japonica, etc.), beardless (Siberian, Japanese, Louisiana, etc.), and bulbous (Dutch, juno, reticulata, etc.).

  • Bearded irises are shipped dry. These irises can be moved at any time during the growing season, though they are traditionally divided about 6 weeks after bloom. It's important to get them replanted into their new garden at least 6-8 weeks before freezing weather to give them time to root in adequately before winter.

    Use a spade or fork to dig up your iris clumps and wash them off well with a hose until you have removed all dirt and can easily see where the rhizomes (rzs) are attached to one another. With a sharp knife, cut through the attachments (or you can break them apart with your hands, but a sharp knife will make a smaller, cleaner wound). Inspect the rzs thoroughly. Discard any rhizomes that are soft or mushy or show any other signs of disease, any that do not have viable roots, and any that are just too tiny to bother with. Many folks also discard any rzs that have already bloomed (they will not bloom again, though they may grow additional increases). Remove any dead, spotted, or unhealthy (brown or yellow) leaves, and wipe off any insects on the remaining leaves. Cut the leaf fan back just enough to accommodate the size of your shipping box without having to bend or fold the leaves. Snip off any dead roots but leave the plump roots intact. As a preventative measure to avoid transmitting any plant pests or diseases to your trader's garden, soak the rzs in a solution of 1 part household bleach to 9 parts water for 20 minutes, then rinse in clear water. Dry the leaves and, using a permanent marker, write the name or description of the plant on a single, central leaf. Avoid writing across several leaves or on the outer leaves of a fan. As leaves dry, they tend to separate from each other, and the outer ones shrivel and die.

    After you have separated, inspected, cleaned, and labeled your rzs, lay them out in a shady, dry area for a couple days to allow the cut wounds to scab over and the plants to dry thoroughly. It is extremely important to ship only completely dry plants, as any dampness (even moisture retained between the leaves) can result in mold and rot developing in transit. Once your plants are completely dry, pack them loosely into a box using a minimal amount of a breathable and absorbable packing material (excelsior, dry wood shavings, crumpled or shredded newspaper - avoid styrofoam packing materials). Punch holes in the box to allow good air circulation, and your irises are ready to travel to their new home.

  • Crested irises may be shipped either dry for larger species such as Iris tectorum, or with the rhizomes and roots kept damp for smaller species such as Iris cristata. These irises can be moved at any time during the growing season, but it's probably best to do so immediately after bloom is finished. It's important to get them replanted into their new garden at least 6-8 weeks before freezing weather to give them time to root in adequately before winter.

    Use a spade or fork to dig up your iris clumps and wash them off well with a hose until you have removed all dirt and can easily see where the rhizomes (rzs) are attached to one another. Depending on the size of the rzs, you may wish to divide them either into small clumps or individual rhizomes. With a sharp knife, cut through the attachments. Place rhizomes of small crested species into a bucket of water to prevent them from drying out. Inspect the rzs thoroughly. Discard any rhizomes that are mushy or show any other signs of disease and any that do not have viable roots. Many folks also discard any rzs that have already bloomed (they will not bloom again, though they may grow additional increases). Remove any dead, spotted, or unhealthy (brown or yellow) leaves, and wipe off any insects on the remaining leaves. Cut the leaf fan of larger crested species back just enough to accommodate the size of your shipping box without having to bend or fold the leaves. Snip off any dead roots but leave the plump roots intact. Dry the leaves and, using a permanent marker, write the name or description of the plant on a single, central leaf. Avoid writing across several leaves or on the outer leaves of a fan. As leaves dry, they tend to separate from each other, and the outer ones shrivel and die.

    After you have separated, inspected, cleaned, and labeled your plants, wrap the rhizomes and roots of smaller crested species in damp (not wet) paper towels or peat moss. Place the wrapped rhizomes and roots in a plastic baggie or plastic wrap, securing snugly around the base of the leaves. Pack the prepared plants loosely into a box using a breathable and absorbable packing material (excelsior, dry wood shavings, crumpled or shredded newspaper - avoid styrofoam packing materials). Punch holes in the box to allow good air circulation. Ship crested irises to arrive as quickly as possible to avoid having the roots and rhizomes of smaller species dry out in transit.

  • Beardless irises are shipped with the rhizomes and roots kept damp. These irises should be transplanted only in early spring or early fall when air temperatures are moderate. It's important to get them replanted into their new garden at least 6-8 weeks before freezing weather to give them time to root in adequately before winter.

    Use a spade or fork to dig up your iris clumps and wash them off well with a hose until you have removed all dirt and can easily see where the rhizomes (rzs) are attached to one another. Depending on the size of the rzs, you may wish to divide them either into small clumps or individual rhizomes. With a sharp knife, cut through the attachments. Place all rhizomes into a bucket of water to prevent them from drying out. Inspect the rzs thoroughly. Discard any rhizomes that are mushy or show any other signs of disease, any that do not have viable roots, and any that are just too tiny to bother with. Many folks also discard any rzs that have already bloomed (they will not bloom again, though they may grow additional increases). Remove any dead, spotted, or unhealthy (brown or yellow) leaves, and wipe off any insects on the remaining leaves. Cut the leaf fan back just enough to accommodate the size of your shipping box without having to bend or fold the leaves. Snip off any dead roots but leave the plump roots intact. Dry the leaves and, using a permanent marker, write the name or description of the plant on a single, central leaf. Avoid writing across several leaves or on the outer leaves of a fan. As leaves dry, they tend to separate from each other, and the outer ones shrivel and die.

    After you have separated, inspected, cleaned, and labeled your plants, soak them overnight in a bucket of clean water to make sure they are fully hydrated for their trip to their new home. After soaking, wrap the rhizomes and roots (not the leaves) in a wet paper towel, damp peat moss, or hydrated polymer crystals. Place the wrapped rhizomes and roots in a plastic baggie or plastic wrap, securing snugly around the base of the leaves. Pack the prepared plants loosely into a box using a breathable and absorbable packing material (excelsior, dry wood shavings, crumpled or shredded newspaper - avoid styrofoam packing materials). Punch holes in the box to allow good air circulation. Ship beardless irises to arrive as quickly as possible to avoid having their roots dry out in transit. Upon receipt, beardless irises should be soaked in a bucket of fresh water overnight before planting.

  • Bulbous irises are shipped dry. Most bulbous irises are handled similarly to tulips or daffodils. Dig dormant, mature bulbs in summer after the foliage has died down. Rinse off all soil and remove dead foliage. Inspect bulbs for signs of disease or insect damage, keeping only healthy bulbs for trading and replanting. Juno irises require a bit of extra care as they have both bulbs and fleshy roots. Care should be taken to dig these irises with the fleshy roots intact and to package them carefully to avoid bruising either bulbs or roots in transit.

    Allow bulbs to dry for a couple days before packaging for shipping. Pack them loosely into a box using a breathable and absorbable packing material (excelsior, dry wood shavings, crumpled or shredded newspaper - avoid styrofoam packing materials). Punch holes in the box to allow good air circulation. Bulbs should be replanted in mid to late autumn.