Dividing Iris and Daylilies
Allan Robinson: Ask a Master
Gardener
Tuesday, September 26, 2017
Q: When should I divide my
irises and daylilies? And how should this be done? Francis R., Tulsa
A: Irises Of the many types of irises, the most commonly grown are hybrids or bearded irises. Bearded irises are the ones that have a hair-like structure on one of their lower flower blades, along with showy, multicolored blossoms.
They usually bloom in spring or
early summer but then go dormant until the fall. These irises should be divided
every three to four years during late summer to early fall.
Irises have a root-like structure
called a rhizome from which they reproduce. It is a slender potato-like
structure. As a plant grows and blooms, it produces small baby rhizomes at the
edge of the mother plant.
It’s these young rhizomes that
produce new plants. The mother rhizome will not bloom again. These new rhizomes
will have small buds where they will produce new plants.
To divide: Dig up the whole structure, trim the iris blades
to 6-8 inches in length and separate out the new rhizomes by cutting or
breaking away from the parent structure. The goal is to get young rhizomes that
have one to three small buds, along with a few healthy leaves and some roots.
Discard the rhizomes that are mushy or appear diseased.
To prepare the soil: The new planting area should be prepared
beforehand. Irises do well in a range of full sun to afternoon shade, but they
must be planted in well-drained soil to prevent rot. If you have a clay soil,
incorporate several inches of organic compost to aid in drainage. A
slow-release fertilizer mixed into the soil is optional, but beware that too
much nitrogen will increase disease susceptibility.
When planting, cover the roots
well, but the rhizome should be shallow, preferably less than 1 inch deep with
the top of the rhizome slightly out of the ground. If planted any deeper, it
likely will not bloom. Do not mulch, as it may cause disease.
Dividing and transplanting
bearded irises will improve health and produce more blossoms, but be aware that
they may not bloom the first year after moving.
Daylilies
Division of daylilies, as well as
hostas, may be done in either the spring or fall. But in our area, fall
division is preferable as replanting will allow for considerable root growth
before next spring.
Before digging, trim the leaves
to 6 inches or so and water the plants to loosen the soil. Dig the plant with a
large root ball and wash the soil from the roots with a hose. This will allow
you to tease out individual plants without cutting them. The goal is to have
plants with three or more leaf fans and a healthy-looking clump of roots. A
large clump of daylilies may yield several new plants for you and your
gardening friends.
When replanting, prepare your
site beforehand by mixing in a generous amount of good organic compost and
making sure the new location will get several hours of sunlight. Adding a
slow-release fertilizer into the soil at planting is optional.
Garden tips
·
Begin preparing
your outdoor plants for a move indoors. Move houseplants indoors when the
outside and indoor temperatures are about the same. For plants in full sun,
move to shade. Begin with light and then heavier shade over a week’s time to
prepare the plant for the low light indoors. If you move the plant from full
sun to a low-light indoor situation, the plant may experience “shock,” lose
leaves and perform poorly inside.
·
Inspect plants
for insects and disease and treat accordingly. In many cases, a few insects can
be controlled by hosing down the plant and removing by hand. Another option is
to use an insecticidal soap spray. This is effective and safe for you and your
plant.
·
Also consider
drenching the pot with 2-3 pot volumes of water to help remove insects and
residual fertilizer salts.
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