Planting Your Rhizomes
Prepare The Bed:
Prepare a neutral to slightly alkaline soil bed at least 10" deep; mixing in a 5-10-10 fertilizer at this time is recommended.
Ideally, the soil needs to be firmly packed down yet crumbly for ease of cultivation. Rhizomes planted in soil that is too loose tend
to settle below the soil line which may lead to diminished performance. Soil that is too heavy may lead to stunted growth and health
issues. However, irises are pretty darn tough and often thrive under conditions that are contrary to these recommendations. The
iris will let you know if it doesn't like where it's growing!
Depth To Plant:
In the Pacific Northwest, planting the rhizome so that it is partially exposed (like a duck on water) is recommended. For rhizomes
that have long roots, it is easiest to dig your planting hole, build a mound of soil (peak level with planting bed soil level) in the
center of the hole, place your rhizome on top of the mound, spread the roots over the mound and then fill soil around the roots,
packing it firmly as you go. Newly-set plants should be kept moist until the roots are growing well. Note: freezing weather may cause
"heaving" of the soil. Simply press the rhizome back in to soil level.
In regards to individual plants, the closer the plants are, the sooner dividing will be required (3-4 years) and heavier fertilizer
will be needed. Greater distance between plants will mean more time before dividing is needed (4-6 years) but the bloom impact
will not be as significant for at least 2-3 years. If you are planting for mass impact (3 or more rhizomes; triangular planting
pattern), the same considerations will apply, but chances are division will be needed sooner. For close or mass planting, we
recommend 8" apart for MDBs, 12" apart for SDBs, 18" apart for IBs, BBs and MTBs, and 24" for TBs. The best
planting time is July through August in the Pacific Northwest area; sooner is better to allow the plant to become re-established for
next year. When dividing, dig the plant, remove and discard the old center rhizomes and replant the new fans. You may cut out the old
centers with a knife while they are in the ground if you do not wish to lift the plant. If you choose to follow this procedure be
sure to sterilize the wounds with a 5% bleach solution or a Clorox wipe and allow to dry before soil covers the remaining rhizomes.
First Year Care:
Until the plant is well established, extra care may be necessary. If a bloom stalk is produced the first year, you may want to
consider removing it so the energy will be directed to growing strong roots and increases for the following year. If the plant is
healthy and well established, and you decide to jeep the bloom stalk, staking the stalk is highly recommended to help prevent the
weight of the bloom from uprooting the rhizome if it falls over. Please keep in mind that allowing bloom the first year may lead
to bloom-out, where the rhizome and plant are so taxed that they die or fail to perform well for several years.
The most common questions about bearded irises is when to divide and how to divide. In the Pacific Northwest, dividing of bearded
irises can be done any time of year as long as the ground can be easily worked. However, the best time
to divide is from mid-July to the end of August. This time-frame provides the best conditions for the plant to re-establish itself before the cold
weather sets in; the earlier the dividing and replanting is completed, the better! When dividing, dig the plant, remove and discard
the old center rhizomes and replant the new fans. If the clump is getting crowded, but you don't what to dig and divide yet, you may cut
out the old centers with a knife while they are in the ground. If you choose to follow this procedure be sure to sterilize the wounds with
a 5% bleach solution or a Clorox wipe and allow to dry before soil covers the remaining rhizomes.
- Dig the clump. Trimming the foliage by half before digging will ease handling.
- Knock off as much loose soil as possible. Wash off remaining soil with water.
- Break off healthy rhizomes from old rhizome, or cut off with a sharp, sterile knife. Save only the healthiest for replanting!! Donate or compost the rest!!
- Neatly trim foliage to about 6". A pointed top is traditional.
- Replant in triangular pattern, cut rhizome ends to the inside for a good-sized clump.
- Keep weeds and grass tufts out of the rhizome clumps.
- Cultivate shallowly, since the feeder roots are near the surface.
- While considered to be drought tolerant, established plants benefit from regular watering as this promotes rhizome growth and
helps maintain attractive green foliage.
- Fertilizer should be applied as a side dressing in early spring, and then again after bloom. It can burn rhizomes, so apply
it around, but not on, the plant or rhizome. Too much nitrogen promotes soft, lush growth which is susceptible to rot, so a
5-10-10, super phosphate or similar low-nitrogen formula is best.
- Air circulation and sanitation are the best problem preventatives.
- Remove old iris leaves and other debris from around the base of the plant.
- Aphids, caterpillars, etc. may damage the flowers, but rarely do serious harm to the plant.
- Slug control is essential. Slugs love to nibble at new shoots and will even climb and attack the tall leaves of some varieties.
- Old bloom stalks need to be cut or broken off at ground level once bloom is complete.
- Healthy, green foliage should NOT be cut off. It needs to be left on the plant to promote and support development of new
sprouts (increases) for the next season.
- During the growing season, the plants may be sprayed, along with roses and other perennials, with a combination
insecticide-fungicide spray at regular intervals - usually 10 days to 2 weeks. Leaf spot may flourish in warm, wet years, making
the leaves unsightly. Cutting off the spotted leaves will improve the appearance of the garden and retard the spread of disease.
To help limit the spread of this disease, be sure to sanitize the pruner/scissor blades with a disinfecting wipe when moving
from plant to plant!
- Mulching of bearded iris is to be avoided. If you desire to mulch, do not cover the rhizomes. The sun must reach them to
facilitate development of next year's increases. Freezing weather will not harm the rhizomes, other than causing slight
"heaving" out of the ground. If this occurs, simply cover the exposed roots with additional soil.