The Backyard Gardener: Divide and conquer the iris
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Hello Mid-Ohio Valley farmers and gardeners! Cooler temperatures prevail this week as we say goodbye to July and hello to August. I want to send a big thank you to all the supporters of our 4-H and FFA livestock program here in Wood County.
We had a successful week at the Wood County 4-H and FFA Summer Showcase where youth display their talents and their animal projects. We appreciate the community support of 4-H and FFA. These programs build lifelong skills in our local youth including responsibility, decision making, self-confidence, people skills, sportsmanship and problem solving.
This week I want to talk about dividing iris plants. Late July and August is also a great time for backyard gardeners to divide other perennials such as daylilies, peonies, purple coneflower, and coreopsis.
Dividing herbaceous perennials has numerous benefits. First, plants will be healthier and live longer. It rejuvenates older, tired plants by stimulating new growth, improving flower production, and encouraging stronger stems.
A major advantage is it helps control a plant's size. Perennials can eventually outgrow the space originally allotted to them, resulting in overcrowding.
Furthermore, division is a reliable vegetative propagation method that results in exact duplicates of the original plant in terms of bloom time, flower color, shape, size, and habit. Finally, the divisions you plant or give to family or friends are free (minus some elbow grease).
Irises are an easy-to-grow, long-lived, and relatively carefree perennial flower. They can be found in a variety of colors, ranging from pink, purple, yellow, peach, green, white, tan, bronze, to almost black, and bicolor.
The most common type of iris grown are bearded irises. They are well adapted to the Mid-Ohio Valley, require minimal maintenance and bloom beautifully each spring.
However, after several years irises will outgrow their allotted space. The center of plants tend to lose vigor and begin to die out. In addition, the overall number of blooms will decrease, primarily only being found on the outside of the clump.
At this point dividing the iris is necessary, the process of splitting a single plant into multiple plants to stimulating new growth and prevent overcrowding.
The frequency of dividing depends on plant growth. However, as a rule of thumb, iris should be divided every 3-5 years to rejuvenate them and increase flowering. Iris should ideally be divided from late July through August.
During this period, iris plants are dormant and will most likely still bloom the following year. If divided too soon after flowering, gardeners will tend to see a reduction in flowers during the next bloom period.
Iris plants have a root system that consists of thick rhizomes and smaller feeder roots. Rhizomes are modified stems that grow just below the soil surface. Plants with thick tuberous roots or rhizomes should be cut apart using a sharp knife. Rhizomatous plants also include dahlias and canna lilies.
Each division must have a growing point or bud. For irises, you must cut or break off the divisions from the "parent" rhizome and replant them so that the roots are spread out and the rhizome is sitting slightly above the surface of the soil.
A few tips before digging up plants. Ideally, divide perennials on a cool, cloudy day. Water the plant the day before you divide it so that it is fully hydrated. Dig up the parent plant by inserting a shovel or spade straight down into the soil at the drip line. Depending on the plant, the drip line can be several inches to a foot or more from the plant crown.
Iris plants are fairly shallow rooted, so it should be easy to dig up the entire clump when dividing. Dig up the entire plant and shake off the excess soil to examine the roots. Look for healthy sections of rhizomes that have a fan of leaves growing from the top side of the rhizome, and feeder roots extending below.
Healthy rhizomes should be firm and at least the width of your thumb. With a sharp knife, or with your hands, break off sections of rhizomes that have the fan of leaves attached to them. Each of these sections is a viable plant that can be replanted in your garden.
Some sections of rhizome may have two fans, and those are great to plant as well. These larger sections will bloom more than the smaller pieces but will also need to be divided sooner too.
Sections of rhizomes without a fan of leaves attached can be discarded. Any pieces of rhizome that are soft and mushy, have holes (caused by iris borer), or with an odor should also be discarded.
Next, trim the leaves of the plant to a length of about 8 inches tall. Cut the fan of leaves in a triangle shape, with each blade being cut at an angle to keep water from collecting in the thick, open leaves. This step will help prevent the plant from falling over while the roots become established.
Plant divisions right away in holes that are 2-3 times wider but no deeper than the root ball and with the crown just slightly above the soil level. Plant rhizomes shallow, making sure the small feeder roots are in contact with the soil, and the rhizomes are only partially covered. The top of the rhizome must be slightly exposed to sunlight when planted.
Firm soil so that there's good contact with the roots and to eliminate any air pockets. Space plants 12 to 18 inches apart in a circle. Direct the cut ends of the rhizomes to the interior of the circle, and the fans pointed out away from the circle so that plants have room to expand.
Water newly planted rhizomes thoroughly once established. Keep in mind it is important to replant irises early enough in the season to allow roots to establish before the first hard frost. It may take one growing season for single fans to build up strength and maximize the number of blooms.
Contact me at the Wood County WVU Extension Office at 304-424-1960 or e-mail me at jj.barrett@mail.wvu.edu with questions. Good luck and until next time, Happy gardening!