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Starting Bearded Iris In Pots
By Walter Moores

Walter Moores grows and hybridizes irises at his Moores’ Enid Lake Iris Gardens near Enid, Mississippi. Some of his iris introductions include: LEMON CHESS '96 which has won two Exhibition Certificates (1994,1995) and an Honorable Mention in 1998. The dramatically colored ASCII ART is a recently registered hybridization of Walter Moores which was introduced in 1997. Another iris some may be familiar with is his TB intro CONFEDERATE ROYALTY. This article previously appeared in the TB Iris Society’s "Tall Talk Newsletter". Some benefit may be derived from potting iris even in our more northerly Canadian climate.

About ten years ago I wrote an article for the AIS Bulletin in which I described some techniques for starting bearded irises in pots. Also, in the last year, I discussed the process with the Iris-L chat group on the Internet. Bob Stroham of Louisville, KY, followed up with an article on clay pot culture in the Spring 1998 Region 7 Irisarian.

Over the years the reasons for potting irises to give them a head start in growth have remained constant, but the techniques have changed somewhat. What follows is my experience with potting irises for over twenty years.

Why Do I Pot?

I agree with Bob that when the new irises arrive, "It’s over 90 degrees, the ground is too dry and hard to dig, and we’re leaving for a vacation trip tomorrow anyway." So, if you live in the hot, humid South or Southwest and you bought a $45 introduction, you need to think seriously about setting that plant or any other for that matter out in the broiling heat. The alternative is to pot incoming rhizomes and to place the pots in a shady location.

Potting irises has unexpected rewards. While it is so hot at planting time, winter weather and rhizome heaving seem remote. But that extra step of potting back in July and August to protect rhizomes from heat will eliminate rhizome heaving when the ground goes through the freeze/thaw cycles of winter. The root systems developed while the irises were potted will enable the plants to remain where they were planted. Potting does reduce losses during these two susceptible seasons. If bloom is expected on first year plants, potting them and getting them established early makes bloom a sure thing. There are more reasons for potting irises than not, and growth and bloom seem to be the priorities for doing so.

The most desirable month for planting or transplanting irises in hot climates is September, when cooler temperatures make it more bearable to be outside, but it is often difficult to find a commercial source that still has blooming-size rhizomes for sale. Also, it has been my experience that when I have ordered early and requested late delivery, I have received inferior rhizomes. I have also had cancellations or gotten substitutes when I ordered in early spring and requested late August or September delivery. Typically, September is the driest month in the South, and the thirst of newly planted rhizomes can cause an added expense by inflating the water bill. So, to ensure you get quality plants of desired varieties, order early and pot the rhizomes. The boost the rhizomes get while in pots will almost guarantee first year bloom in your garden.

How I Pot

When a box Iris rhizomes arrives, open it immediately and check the rhizomes for mold or rot. If you find any, trim it off. Also, cut or shave off all roots. Then prepare a mixture of one part liquid bleach to nine or ten parts water. Soak the rhizomes for at least thirty minutes. Allow the plants to air dry before planting. The clorox bath is necessary to kill any rot potential that might have developed in transit and to prevent it from forming while the irises are potted. Plants may stay out of the ground indefinitely, but if a good head start is desired, the rhizomes should be planted within a day or two of receiving them.

For years at iris sales or auctions I had always seen a few irises potted in black plastic pots. I used gallon pots when I first started potting irises, for I thought I needed at least a gallon of soil for the plant to survive. I did not trim the roots, nor did I provide a bleach bath. Most of the time I just used garden soil that became as hard as a brick when the pots dried out. At planting time it became a chore to move the heavy pots to their blooming spot and to dig a hole large enough to accommodate the contents of a gallon pot. After experimenting with a few four inch plastic pots, I have decided that they are perfect for the potting procedure. I have not found a rhizome too large to fit in one. If a rhizome has a ‘snout’, an extension of growth on the toe, cut it off and consider it to be a second rhizome and plant it in the same pot with the mother rhizome.

The potting mixture should neither be friable or compact. A happy medium consists of one-third Magic Earth (a potting soil with fertilizer), one-third garden soil, and one-third sand mixed well. No other fertilizer is necessary.

Place soil mixture in four inch pots up to the rim and soak with water. The soil may settle and more may be needed. Set the rootless rhizome half exposed in the soil and firm it with your fingers. Make sure the soil level is at the top of the pot so no water can stand in the pot. It would be almost impossible to place a rhizome in such a small pot if it still had the roots intact. New roots will form quickly and wrap around and around the soil in the pot. Tag or label the plant as usual.

Watering the plants may become necessary depending on the weather. It is best to water the pots from the bottom up. Add water to a level of three inches in a galvanized tub, and place the pots in the tub. Allow the water to be absorbed through the drainage holes. Remove the pots when the soil is damp.

It is important to move the pots occasionally so roots don’t find anchor through the drainage holes. A few weed seeds may sprout, but these are easily removed.

Plants may be left in the pots until October to be planted where they are to bloom. In the meantime, preparations should be made for the iris beds or rows that will accommodate the new plants when it is time to unpot, one tap with a trowel will loosen the soil and root ball. That same trowel should have been used to dig a hole about four inches deep. For an extra boost, alfalfa pellets or a balanced fertilizer might be added to the planting hole. Firm the soil around the plant and water.

In summary, many people would consider potting irises to be double trouble. It really isn’t when one considers the growth and bloom potential of the potted irises over the traditionally planted irises. Losses are almost nonexistent.