Garden Dilemmas, Delights & Discoveries, Ask Mary Stone, New Jersey Garden blog

Dividing Iris

Purple Siberian Iris in front of a barn

Hello Fellow Readers, Especially now, I encourage you to find respite amongst the miracles of nature. And in our gardens, for those who like to dig in the dirt.  Dividing Iris can be a perfect therapy.

Dividing Purple Siberian Irises in rock garden

It’s a delight when the Siberian Iris emerge in the garden.

It’s a delight when the Siberian Iris (Iris sibirica), planted by the previous owner, emerge in the rock garden and flourish with deep purple flowers. But in the last handful of years, there are not nearly as many blooms. The same is true of the fragrant white Bearded Iris (Iris germanica) hand-me-downs from a dear friend. Yes, dividing them is long overdue. But the task seems daunting, so (here comes a confession) I have never made the great divide.

I’ve divided many other plants, including Hosta which is fun using a small ax to hack the roots apart, which sounds a tad violent perhaps. But Hostas are quick to recover and are very tough plants. Bambi loves them though, so a rotation of my two favorite natural dear sprays, Deer-Off and Dear-Off, keeps them away.

The best time to divide Iris depends on what kind of iris

Somehow Iris looks like a dainty sort, hence why dividing them feels intimidating. Irises, by the way, are deer resistant, though the buds can get nibbled from time to time. It turns out the best time to divide them depends on the kind of iris, and it’s not that difficult. So please don’t let the following “recipe” intimidate you.

Dividing White bearded iris in garden

Bearded Iris hand-me-downs from a dear friend.

But how to divide iris is universal

Bearded Iris should be divided every three to five years. The best time is late July through August so as not to miss out on the spring blooms. (Yay, I’m off the hook, for now, :^) After cutting back the leaves to a third of their height, dig up a clump, then wash off the dirt from the underground stems called rhizomes. Pull them apart by hand or by using a sharp knife, being sure each division has large, firm rhizomes, and two to four fans of leaves with each clump. Toss unhealthy or insect ridden rhizomes. There’s an iris borer, which is a stealth pink caterpillar that feeds inside rhizomes, often leading to bacterial soft rot. So, squeeze the root even if they look okay from the outside.

Plant the divides right away. Dig holes the size to accommodate each split, typically about five inches wide and deep, spacing them sixteen to eighteen inches apart, creating a mound of soil in the middle. Sit the rhizome on the mound and spread out the roots. They prefer full sun and well-drained soil, so add compost to clay soils. Each rhizome should be just below the surface after you cover them with soil. Water them thoroughly and do not add mulch on top, which can retain moisture and encourage rot.

Flower of Purple and White Bearded Iris to be dividedSiberian irises don’t need dividing as often as Bearded Iris.

I think the narrow grass-like leaves of Siberian Iris are more appealing in the garden after flowers are spent compared to the sword-like foliage of Bearded Iris. But both are beautiful in bloom. Siberian irises don’t need dividing as often as Bearded Iris. But when they bloom less, have bare centers, and become crowed like mine, its time. It’s the same technique as their bearded cousins though they are deeper rooted. The best time in colder zones such as ours is early spring, just when the foliage starts to emerge. The second-best time is late summer, but NO MORE PROCRASTINATING Mary.

Besides, dividing Siberian Iris takes some muscle excavating up their deep roots. You may need to bring out your garden spade and jump on it around the outside of your clump before digging it out. But hey, its good exercise and exercise and being outside is good therapy. Stay well, dear friends. Garden Dilemmas? (and now on your favorite Podcast App.)

Click through to learn about Dividing Perennials
Click through to learn about Our Native Irises on the USDA website.

Mary Stone, owner of Stone Associates Landscape Design & Consulting. As a Landscape Designer, I am grateful for the joy of helping others beautify their surroundings which often leads to sharing encouragement and life experiences. These relationships inspired my weekly column published in THE PRESS, 'Garden Dilemmas? Ask Mary', began in 2012. I dream of growing the evolving community of readers into an interactive forum to share encouragement and support in Garden and Personal Recoveries - seeking nature’s inspirations, stimulating growth, weeding undesirables, embracing the unexpected. Thank you for visiting! Mary

Leave a Reply


This site uses Akismet to reduce spam. Learn how your comment data is processed.