Planting and Growing Siberian Irises
Your New Plants Arrive
When you receive Siberian irises from a good source, the roots will be wrapped in
some way to keep them moist. Remove the wrappings as soon as you can, and
soak the division in a bucket of water deep enough to cover the roots.
Plants may stay in the bucket of water (Change the water daily if possible.)
for up to a week.
It is critical for there to be adequate moisture during the establishment
period. Make sure the newly arrived plants have soaked at least a few hours.
Plant directly in the new location if you and your weather will be
able to keep the soil wet continuously until new growth appears. Another technique
is available too, and is highly recommended:
a trick of the experts
Pot the new irises in a half-and-half mixture of a good potting soil and
the soil they will eventually grow in, and water well. Place the entire pot
in a saucer of water. If you have many of them, a tub or a child's swimming
pool will work too. Maintain an inch or two of water, and change the water
every couple of days. Roots should develop and you should see new growth in
two to four weeks. Then, the transfer of the plant to its new bed, soil intact,
should be an easy transition.
Most irises will grow and bloom better if planted in a sunny location. Siberian irises prefer a rich soil
with ample organic matter. If the soil is clay, the addition of organic matter will help to loosen it. If
the soil is more sandy, the organic matter will help in water and nutrient retention. Depending on what is
available, till in an ample amount of manure, hay, straw, peat moss, compost, etc. If using hay, straw, or
wood products, you
may need to add high-nitrogen fertilizer to compensate for the nitrogen tied up in the decomposition process.
In a small garden, it works well to add some peat humus (Michigan peat).
The soil should be slightly acid (pH 5.5 to 6.5 is good). If your soil pH is too high, it can be lowered by the addition
of granular ferrous sulphate or agricultural sulphur. Avoid planting Siberians when the soil temperature is too high;
mid or late autumn may be better than early autumn in the warmer zones.
Plant these irises in a naturally moist area, or in an area where you can water the new
plants until they become established. Planting in a small depression (1 to 3 inches below the average soil
level) will help the plant receive extra water during rains or when watered. The roots should at no time
be allowed to dry out during transplanting. Do the planting in the cool of the evening if possible. If the
weather is very hot, it might help to shade new transplants in some way, maybe with a
webbed lawn chair.
Tip for the fanatics
Adding some alfalfa pellets or alfalfa meal to your soil may prove beneficial. Besides its low concentration of
nutrients, the alfalfa contains triacontanol, a natural growth stimulant.
Plants should be fertilized only lightly when planted, if at all. (The later you plant in the fall, the less
fertilizer should be used.)
Follow this advice to keep your new Siberian growing smoothly:
- Siberian irises are moderate feeders. A liberal application of a balanced
fertilizer, such as 10-10-10, in spring and just after bloom is beneficial.
After planting, mulch at 1 to 3 inches. Oat straw, pine needles, rotted sawdust or wood chips are recommended.
The mulch helps conserve moisture as well as reduce weeds. Do not mulch with peat moss or grass clippings as
both can pack down and become impervious to water.
Once established and mulched, most Siberians can get along with as little water as bearded irises, and
are able to withstand droughts with minimal supplemental water. More water, however, is fine too.
After bloom is complete, cut off the stalks near the ground on a dry day. Some people find leaving
the stalks in place a while to be attractive; if you do this, be sure to remove the pods before the
seeds drop and produce seedlings that are not quite true to the variety you planted.
After the foliage has browned in the fall, cut it off an inch or so from the ground.
Vigorous Siberians should be divided after three years, or the task will become more difficult.
Dividing mature clumps can often be accomplished by the two-pitchfork method. More moderately
growing varieties can remain undivided for five years or more.