As boxes of rhizomes arrive at homes around the country, and gardeners talk about their new treasures, the discussion sometimes turns to the practice of potting. Some gardeners view potting rhizomes as an unnecessary extra step. Other gardeners view it as an integral part of their iris gardening. Though the practice was once considered unusual, it appears that many gardeners have added potting to their gardening routine as they learn more about the potential benefits offered. But, just how many? A recent survey of iris enthusiasts showed that 12% of respondents potted all of their newly dug rhizomes each year. Another 10% responded that they potted any rhizomes that required special care. The remaining 78% indicated that they planted all of their rhizomes directly in the garden. With 22% of respondents potting to some extent each year, let’s take a closer look at the “why” and “how” of this practice.
Of that 22%, the majority indicated that they employed potting to help protect newly dug rhizomes from extreme environmental conditions while establishing new roots. In the South and Southwest, gardeners wanted to minimize exposure to excess heat and humidity. In many cases, these gardeners also wanted to delay the chores of reworking the soil and planting until the cooler weather of fall. In the North, gardeners potted rhizomes that arrived late in the season, when planting directly in the garden increased the risk of freeze damage. Gardeners who indicated they employed potting with rhizomes that were small, with rhizomes that appeared to be struggling in some way, and with rhizomes that warranted special care came from all geographic regions.
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.  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 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.
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, 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.
The author has given his permission for this article
to be reprinted for educational purposes. |
Mr. Moores 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 accumulation."
Additional Notes:
Magic Earth is recommended in the article above, but it is no longer
available. Magic Earth had a guaranteed analysis of 9-6-5. As a
substitute, look for an organic potting soil with a similar analysis,
such as Miracle Gro Organic Potting Soil. Do not use Miracle Gro's
standard potting soil, as it typically has too much nitrogen for use
with bearded irises. Once you have selected an appropriate potting soil,
it can be amended to best suit your climate. Common amendments used
when potting bearded irises include Canadian sphagnum moss, coarse sand, horticultural
vermiculite, bone meal, dolomitic lime, Super Phosphate, and granular fungicide. If adding fertilizer, choose one that is slow-releasing and low in nitrogen. Select free-draining pots from 4" to 6" in diameter.
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