Perhaps the most widely read information about potting
rhizomes was written almost twenty years ago by Walter Moores, who grows and hybridizes
irises in Yalobusha County, Mississippi. Mr. Moores has introduced almost 90 cultivars
since 1977, and 18 of those have received AIS awards. His earlier work focused on
reblooming irises, some of which can still be found in commercial catalogs today --
almost 40 years later! His recent work focuses more on tall bearded irises and species
crosses. Having written about the subject of potting in an issue of the AIS Bulletin,
Mr. Moores followed up with an article in the Tall Bearded Iris Society's Tall Talk
(September 1998). Demonstrating that this information can prove useful in diverse
climates, the article has been reprinted by many local clubs throughout the United
States and now also appears on the current webpage of the Canadian Iris Society.
Rather than trying to rewrite a classic, Mr. Moores' original article is presented
here, with just a few additional notes at the end.
Starting Bearded Iris In Pots
By Walter Moores
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 Strohman [of Louisville, KY] 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.
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
How I Pot
When a box of 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.
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, 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.
Mr. Moores has given his permission for this article to be
reprinted for educational purposes. The author recently stated that the
one change he would make to the above article is to add this advice:
"When potting rhizomes, remove the leaves as they die to prevent moisture