Dig this! Iris

The Sun Country Iris Society (SCIS) has completed digging iris rhizomes from 3 or the 4 gardens that were on the Southwest Region 2009 Trek in April. These rhizomes are now being sent to other iris societies in the region as well as being offered to our members at Iris Auction at our meetings. They will also be sold at a number of public sales throughout the fall.

Digging & preparing:
Iris rhizomes are dug to divide large clumps for replanting. Tall bearded irises are often divided every 3 – 4 years depending on the size of the clump. Optimum time for digging is September in the Valley of the Sun. Then they can be replanted soon afterwards. We prefer to plant in October when weather has started to cool. Carefully dig deep under the clump to avoid damaging rhizomes. The original mother rhizome is in the middle and the increases grow out from the mother. The SCIS recommends throwing the mother rhizome and any bloom stalks (heavy stalks that had blooms). Trim the roots off to about a fistful of roots. Trim the top of the leaves (fans) to a V at the top to the fans. In the Valley we usually trim the roots very close before planting.

Digging tall bearded irises:
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1. Carefully dig deep under the entire clump.
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2. Notice the clump grows out from the original mother rhizome.
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3. Separate the soil from the roots of the rhizomes
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Prepare beds for planting:
Choose a location that has 8 hours of full sun for maximum bloom. Dig soil to a depth of 10 – 12 inches.

Soil:
According to the basic iris handbook, the recommendation of pH is 6.1 to 7.2. As a soil chemist I think it is realistic to have a target of 6.5 to 7.3 for pH. Manures as recommended could be a problem. Desert produced manures contain high soluble salts so I like to stay away from that source of organics. They usually contain weed seeds and are not usually composted enough. Mulch that is formulated and inoculated microbially and composted that has low manure content works the best in Arizona soil conditions.
PH adjustment is necessary for most Arizona soils. Typical soil tests show a pH of 7.8 to 9.0 and above. A soil test is the most accurate method to determine the nutrients and soil amendments needed. The soil test I run comes with a prescription for the correct amount of amendments and fertilizer to correct problems. This usually saves money on cost of fertilizers. To adjust the pH use First Step Soil acidifier from Gardener’s World (more info at http://www.gardenpro.net/ information #1 handout)
Another key factor for good soil is the microbial content. Great Big Plants enhances the microbial content of the soil. Great Big plants is organic and contains 17 different microbes, many of which feed on detrimental fungus such as pythium, rhizoctonia and phytophora. You will also notice an increase in the number of worms in the soil because microbes feed on organic matter that contains microbes.
The handbook recommends aluminum sulfate. That should not be used in Arizona soils because it can cause retardation or mutations on iris.

Planting:
Will be covered in October newsletter, as temperatures are more conducive in the Valley of the Sun.