irises prefer a rich soil with ample organic material. If the soil is clay, the
addition of organic matter will loosen it. If the soil is sandy, the organic
matter will help in water and nutrient retention. Depending on what is
available, till in an ample amount of well-rotted manure, hay, straw, peat
moss, compost, etc. Ideally the soil should be slightly acid, pH 5.2-6.4. If
the soil pH is too high, it can be lowered by the addition of granular ferrous
sulfate, aluminum sulfate, or agricultural sulfur.
irises are best transplanted in the early spring as growth is just beginning,
or in the early fall. Some gardeners succeed by transplanting immediately after
bloom in areas where summers are not hot and dry. Generally, fall transplanting
is best for hot regions and spring transplanting is recommended for areas with
cold winters. The roots must be kept moist while out of the ground. If plants
must be held, they can be placed in a few inches of water to cover the roots.
New transplants must also be kept watered once or twice a week until fully
established. Often the leaves of newly transplanted plants will turn quite
brown. This does not seem to hurt the plant and new green leaves should
Siberian irises in a naturally moist area or in an area where they can be
watered until the new plants become established. Planting in a small depression
(1 to 3 inches below the surrounding soil level) will help the plant receive
extra water during rains or when watered.
in the cool of the evening is best. If the weather is very hot, it might help
to shade the new transplants in some way. Established plantings of
28-chromosome Siberians are very drought tolerant.
should be fertilized only slightly when planted, if at all. (The later they are
planted in the fall, the less fertilizer should be used.) Siberian irises are
heavy feeders. Alfalfa (pellets or meal) has proven an effective soil amendment
or top dressing. A liberal application of a balanced fertilizer, such as
10-10-10, in spring and again just after bloom is beneficial. Foliar feeding
with chemical fertilizers like Miracid may help weak plants to grow better.
After planting, mulch at 1 to 3 inches. Oat straw, pine needles, rotted sawdust
or wood chips are recommended. The mulch conserves moisture as well as inhibits
irises will often set seed in pods. Unless these are grown for dried
arrangements, remove the stalks after bloom is over to save plant energy, to
give a neater appearance and to keep unwanted seeds from falling into the
garden. These could germinate and grow into plants that are generally less
desirable than the original variety. Bloom stalks may be broken off at the top
of the rhizomes by pulling them toward the center of the clump, or they may be
attractive fall golden brown foliage can be cut back after a hard frost, or
before new growth begins in the spring. The old foliage makes a natural mulch
for plants in very cold areas but may also provide a warm shelter for rodents,
which will eat the rhizomes and tender shoots.
irises should be divided about every three to five years or when the center of
the clump begins to die out and quantity of bloom decreases. Dividing a mature
clump of Siberians may present problems as the rhizomes often grow very tightly
together. Dig the entire clump and remove several nice divisions from the outer
part of the clump, replant those, and discard the hard center of the clump. If
more divisions are desired, the clump may be broken apart using very strong fingers
or in some cases a heavy spading fork, shovel, hatchet or ax can be used. The
leaves of new transplants should be trimmed to a length of 6 -10 inches