(For Bearded Iris)
(Click here to find out your USDA Plant Hardiness Zone)
Care of Rhizomes:
When the box of iris arrives, unpack it right away and spread the plants out to air on newspapers in your house. Make sure they are kept completely dry until after they are planted. Never put them in the refrigerator. They can be held in the house for 2-3 weeks before planting if necessary, but turn them weekly to keep them aired out and check for aphids on the leaves. It's best, however, to PLANT THE RHIZOMES SOON AFTER THEY ARRIVE!
Time To Plant:
It varies according to where you live and should be 4-6 weeks before the first frost to allow for good root development (and to have a good chance of blooming the next spring). In our zone 4, iris need to be into the ground by the end of July. August planting is okay for us, but there will be fewer increases and flowers. August is great for zone 5 and warmer climates. In areas with very hot summers and mild winters, planting in September and October may be preferable to avoid the extreme heat.
Full sun is best, but iris will still bloom with half days of direct sunlight. In very hot zones afternoon shade may be better, but remember, bearded iris don't do as well near a lot of tree roots. It's a plus to plant in ground that is new to iris, and a slope is beneficial for drainage. Avoid low spots and areas where large snowdrifts can cause water to stand on the bed for more than 2 days during spring thaws. Plenty of air circulation will also prevent rot. You can group reblooming iris together, making it easier to give them the extra water and fertilizer that they need.
Bearded iris need to be well-drained! Loose, deep soil can be accomplished by tilling in well-decomposed organic matter & sand before planting. Be careful about the source of compost. Aged horse manure makes a good soil conditioner plus adds phosphorus and micro-nutrients. Using cow manure is questionable because of its higher bacteria count which may lead to rot in the rhizomes. If your soil has too much clay and gets waterlogged, consider planting on a hillside, in a ridged row, or in a raised bed for drainage. The ideal pH for iris is 6.8 (slightly acid), but a neutral pH of 7.0 is also okay. We've heard that having soil too acidic interferes with appendages (horns, spoons or flounces) on Spaceagers.
Cover the iris rhizomes with one inch (1") of soil in zones 4 & 5 to prevent the plants from heaving out of the soil in cold winters. The tops of the rhizomes can be even with the ground level if you live in zones 6 or 7, and should be visible if your soil is extra heavy. In extremely hot areas, however, cover with 1" of dirt to prevent baking.
Planting & Watering:
Space the rhizomes 12-24" apart and firm the soil around them to fill in air pockets. Newly-planted iris need to be kept moist but not soggy. Give them 1" of water the 1st time to settle the dirt, then about 1/2" twice a week until new growth appears. After the iris are established, 1/2" of water (including rain) per week should be enough. Over watering bearded iris invites rot, which is their biggest enemy. The roots need to breathe, so deep watering at long intervals is better than frequent, shallow moisture.
Use a garden fertilizer with numbers such as 5-10-10, 6-10-10, or 5-10-5, or similar proportions. The first number (nitrogen) must be smaller than the second number (phosphorus) to promote bloomstalks and roots. Too much nitrogen results in large fans with few flowers and it also causes rot. It's better if neither fertilizer nor manure touch the rhizomes themselves.
Sorry, but spring and summer mulching is bad for bearded iris. You'll have to keep up with the weeds by hoe or by
Contrary to what your grandmother used to do, DON'T cut back green leaves in the fall. Bearded iris love cool weather and will store energy until the foliage turns completely brown. Dead and diseased leaves can be trimmed at any time. Letting the brown fans cover the rhizomes over cold winters as mulch is helpful in zones 4 & 5, but ALL dead leaves & debris must be removed from iris beds in the EARLY SPRING before new growth begins (March for us, but earlier farther south). Completely disposing of the leaf trash will go a long way towards curbing rot and leafspot.
Removing stalks after blooming can help prevent rhizome rot and keeps unknown seedlings from causing confusion in the iris beds. Unwanted seed pods are a drain on the plant's energy that could be going toward increases.
Dividing or Moving:
Depending on your local conditions, established iris clumps will get overcrowded and need to be dug up bare root and transplanted every 3 or 4 years. The timing of digging is very important. It is recommended to wait at least 3 or 4 weeks after bloom season before dividing iris. Also remember to allow a minimum of 4 weeks before hard frost in the fall for the transplants to root. Cut the rhizomes apart with a sharp knife, rather than tearing them raggedly. Trim the roots and fans to a manageable length. All rhizome cuts should be air-dried overnight to heal; then the sooner the rhizomes are planted back in to the ground, the faster their recovery.
We hope this advise is helpful to you. We've tried to cover many situations, but remember that everybody's microclimate is unique and has its own priorities to be dealt with.
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Blue J Iris, 955 Cody Ave., Alliance, NE, 69301; (308) 762-4420; firstname.lastname@example.org