Tuesday, September 26, 2017 By: Ask A Master Gardener

Fall a Good Time to Divide Iris and Lilies

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.
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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