SITE AND PLANTING TIME
Bearded irises require a sunny, well-drained location -
raised beds or mounds are ideal. For good bloom, a minimum of six hours of full sun is
needed. The best planting time is mid-July through the first part of September to give
time for good root development before winter (see planting instructons below.) If you must
plant later in the fall, place a half brick (or a stone about that size) on top of the rhizome
(the fleshy bulb-like structure to which both roots and fans, or the foliage,
are attached) before the first freeze This will keep the rhizome from heaving with the
freezes and thaws of winter. Remove the brick in early spring.
SOIL AND PLANTING
Irises will grow in any good garden soil. The pH should be
close to neutral (7.0). when planting, place the top of the rhizome even with
the soil surface with the roots spread out and deeper than the rhizome. An easy way
to accomplish this is to dig a hole about 12 inches deep and 12 inches wide; make a mound
of soil in the center of the hole to just above ground level; place the rhizome on top of
the mound and spread the roots down over the mound; fill in with soil, covering the roots
and rhizome, and water in well. exposing the top of the rhizome to the sun.
A massed effect can be achieved sooner by planting three
rhizomes of the same cultivar (the cultivated hybrid variety) together.
Place them about 8 to 12 inches apart in a circle with the "toes" (the ends
opposite the fans) of the rhizomes facing inward. Each clump of three rhizomes should be
spaced about two feet apart. Irises planted in this manner will probably need to be
divided after their second bloom season. Planted singly, they should be eighteen to
twenty-four inches apart and will probably need to be divided every three to four years.
To divide irises, dig the whole clump with a spading
fork. As you dig, keep each cultivar together to avoid mismatched replanted clumps. (You
can write the name or color on the fans with a permanent marker. It will soon disappear
after replanting.) Separate the new rhizomes (the ones attached to the "mother
rhizome," the central rhizome that produced a bloom stalk this year) from
the "mother." Trim back the fans, leaving 6 to 10 inches above the rhizome. (NOTE:
In years when you do not divide your Irises, most irisarians leave the fins at their full
length. However, if they are unsightly due to leaf spot or other damage, cut them
back, leaving as much of the fan as possible.) Replant as directed above. Most irisarians
discard the mother rhizome since it will not bloom again. If you have the space and it is
still viable, you can replant it - it will sometimes grow more "babies."
Newly planted rhizomes need moisture to help their root
systems become established. Keep in mind that deep watering at long intervals is better
than more frequent shallow waterings. Once bearded irises are established, they normally
don't need to be watered in the Louisville area. (An exception is the remnontant,
or reblooming iris. These should get a total of about an inch of water per week
during the summer to promote good fall bloom.)
Specific fertilizer recommendations depend on your soil
type, but a light application of a low nitrogen formula such as 5-10-5 or 5-10-10, or just
superpHospHate, applied around (not on) the rhizomes in early spring will promote good
bloom and not encourage rhizome rot. Remontant irises may be fertilized lightly after the
spring bloom to encourage good fall bloom.