Many years ago I received a flat of Iris rhizomes from a friend when she was dividing clumps that had outgrown the area in which they were planted. I planted them in the flower border that runs across the back of our yard. For many years they have bloomed, each year putting on a larger show. The past two or three years I have thought that it may be time to divide and replant them. Unfortunately that thought happens when the iris is in full bloom. When the appropriate time comes to divide and replant I have usually moved on to the many chores of summer not the least of which are the high demands of the vegetable garden. But not this year. Iris can be divided any time from late July through September so I ask: is September too late to keep a resolution? I don’t think so. This year I divide (and conquer) the iris.

A crowded planting

There are more than 200 species of iris but the most common in our area are the bearded and Siberian iris. Iris are easy to grow hardy perennials but if they become crowded then they are more disease and insect-prone and flower production is reduced.

I already know that the flower bed in our yard is a good spot for the iris as it is receives full sun and is well-drained. Selecting new areas to put the divided rhizomes into is not a problem. It is always best to have the new site ready to go so that the rhizomes aren’t drying out in the sun while a new plot is dug. The new hole should be about 5” deep with a small mound in the middle of the hole (you will see why in a bit).

The new hole, 5

The new hole, 5″ deep with a center mound

Also, have ready a few marked trays or buckets to put the rhizomes into if you would like to keep track of the different varieties/colors. I have plenty of pictures of the Iris in bloom so that I have a good idea of where the colors currently are in the bed even though all that I can see right now are the leaves.

Tools for the job

Tools for the job

So, what are tools needed for this job? A spade or a digging fork, a pair of shears, a sharp knife, and a bucket of 1:10 bleach/water solution. The first step in the actual dividing process is to cut the leaves back to a third of their height using a pair of garden shears, trimming them into a fan shape. Be sure to dip the shears into the bleach solution often to avoid spreading diseases.  

Cutting the leaves

Cutting the leaves

1/3 of the original height

1/3 of the original height

Next, lift out the entire clump that is going to be divided by getting underneath it with the spade or digging fork. You may need to work around it in a few areas to get under it.

Removing the clump

Removing the clump

Place the entire clump on the ground and take a look at it to decide where it should be divided. It is easy to see which rhizomes have new growth  and which are no longer supporting  any foliage. Using the sharp knife cut away each section of rhizome that will be replanted, dipping the knife into the bleach solution often to disinfect it. Each new rhizome section should have plenty of roots and a fan of leaves.

Cutting the new rhizome

Cutting the new rhizome

At this time it is important to check for iris borers and  the bacterial soft rot that often accompanies them. Each rhizome should feel firm when pressure is applied. If the rhizome gives way easily then that is a sign that there may be a borer. The adult iris borer is a brown and grey moth. It lays its eggs on the iris leaves and plant debris at the base of the iris in the fall where they will overwinter and hatch into tiny caterpillars in April and May. The new caterpillars will crawl up the foliage, chew pinprick sized holes and begin to tunnel their way back down toward the rhizome. Signs of their feeding are streaks that appear tan or water-soaked. By mid-summer the borers can be up to 2” in length and have reached the rhizome. Their feeding allows the entry of the bacterial soft rot that turns the rhizome into a smelly, mushy, mess. Late summer will see the borers moving into the soil to pupate, emerging as adult moths in the early fall. There are some varieties of the Siberian iris that are more tolerant to a borer attack.  

Possible borer activity

Possible borer activity

Scouting and sanitation practices can be the most useful controls.  Look for the tell-tale signs of chewing damage and water-soaked streaks in the spring when it is easy to crush the insect while it is still in the leaf or remove the leaf entirely. If the plant has above ground symptoms in July then dig up and examine the rhizome for signs of borer activity, discarding any that are infested. In the fall remove all plant debris where the eggs might overwinter. If you have an infestation that you feel is severe enough to warrant an insecticide then acephate (highly toxic to bees when freshly sprayed and as a residue) and spinosad (non-toxic to bees when it is dry) are generally recommended. Here is a link to the Virginia Cooperative Extension fact sheet which also includes some images: Iris Borer

And now back to the rhizomes. It’s time to place them into the prepared holes, putting one rhizome section on top of the mound in each hole. Spread the roots out and down and fill the hole with soil. Be sure that you don’t bury the rhizome; it should still be visible from the surface.

Iris rhizome in its new hole

Iris rhizome in its new hole

The fans of leaves are usually planted so that they all face in the same direction. Water each plant thoroughly and in years such as this one, more than once. Newly transplanted iris may need a winter cover of straw to keep the newly planted rhizome from coming out of its new location due to  the thawing/freezing cycles that can happen. Just be sure to remove the straw in the spring. These new plants may not bloom much the first year but after that they should be back to their normal, showy selves.

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Susan Pelton

What a cold and wet Memorial Day weekend! I am not sure if it broke any records but it was 37 degrees F Friday night and I was pretty glad that my tomatoes and peppers were still in pots so I could bring them inside! Sometimes being a bit behind in gardening activities may be for the best!

While finishing planting of the vegetable garden has been momentarily put on hold, that actually gave me a bit of time to observe and absorb what is happening in my flower beds and this weekend, irises are beginning to strut their stuff. I think I fell in love with irises when I was about 4 years old and visiting by grandmother in Buffalo. She had the most amazing purple iris in her garden that that smelled just like grape Kool-Aid. Although that was more than a half century ago, I have always planted or nurtured irises everywhere I have lived.

I am not alone in my iris obsession! Irises have played a prominent part in lore, legend and religion for over four thousand years. According to the ancient Greeks, they were the personification of the goddess, Iris, who was the messenger of the gods and the rainbow which linked earth to other worlds. Iris would escort souls to another life along her iridescent bridge. Iris flowers were placed on the tombs of women and later Muslims planted white irises on the graves of fallen soldiers.

Of the 200 plus species, those most commonly grown in New England gardens are the tall bearded, Siberian, Japanese, netted and crested irises. I have had reasonable success with the bulbous Dutch iris and I. bucharica, native to Afghanistan, as well.

Iris blossoms vary greatly in shape, color and size but their overall structure is similar. Each flower consists of three upper petals called standards and three lower or outer sepals referred to as falls. Irises are divided into two major groups; those arising from rhizomes, which are horizontal stems growing at or slightly below the soil surface, and those growing from bulbs.

Birdhouse garden w old irises

Birdhouse garden w old irises

Some gardeners lament the relatively brief annual flowering period of irises. And it is true that even in good years weather-wise you cannot expect more than two or three weeks of a spectacular show. These folks can be comforted to some extent by choosing early, mid-season and late species and varieties of irises so the blooming period is prolonged. I like to think about it more like a special holiday one looks forward to each year. It just wouldn’t be appreciated as much if it occurred more often. And irises are just too magnificent to be taken for granted.

Taller irises make a nice backdrop for lower growing perennials. Shorter species, like the miniature bearded iris, or the crested iris (Iris cristata) look best planted in drifts in the front of the garden.

As far as the tall bearded irises go, your color choice is virtually unlimited. Lovelier shades become available each year. Also known as, German bearded irises, they prefer a sunny, well-drained site with adequate moisture. They reach two to three feet in height (although the stand at our local bank is at least 4 feet tall!) and come into bloom from mid-May through early June.

Iris 'Cinnamon Girl'

Iris ‘Cinnamon Girl’

Siberian irises bloom slightly later than the bearded irises. They also grow from rhizomes but the rhizomes are quite small and they readily form a fibrous root system. Colors of Siberian irises are somewhat limited compared to their bearded cousins. They range from white to blue, purple, violet and wine red. Their foliage is slender, almost grass-like.

Japanese irises flower in early to mid-summer and can grow up to four feet tall. A fallacy concerning Japanese irises is that they need wet conditions to do well. In truth, they will grow in almost any well-drained, organic, slightly acidic soil as long as adequate moisture is supplied.

Japanese Iris in White Garden

Japanese Iris in White Garden

Another fallacy is that irises should not be fertilized. Mine seem quite appreciative of nutrients both during early spring growth and about a month after flowering. The bearded irises go into a resting stage after they bloom which lasts about a month. Then they begin to produce new roots and leaf buds. Each rhizome only produced flowers once and then it retires to function solely as a food reservoir.

Division of bearded irises is best done in late summer. Use a sharp knife to divide the rhizomes making sure each mature rhizome has one or more new leaf buds attached. Fans of leaves should be pointing in the direction you want the plants to grow. I generally cut back the leaves to six inches or so when dividing to make handling the plants easier. Position the plants so the top of the rhizomes are at or slightly below the soil surface.

While Siberian and Japanese irises are rarely bothered by pests, iris borers can be a problem with the bearded iris. Larvae hatching from eggs laid the previous fall will feed on leaves then burrow into the rhizome creating wounds that can then be colonized by bacterial rot. Infected rhizomes will be mushy and foul smelling. Control consists of removal of dead leaves in the fall or early spring. If borer damage is noticed, usually because of zigzag feeding injury on leaves, dig up the clump, find the larvae and dispose of them. It is a good idea to dig and divide bearded irises at least every third year to scout for these pests.

Blue Siberian Irises

Blue Siberian Irises

Few perennials are as hardy as irises and provide you with a rainbow of color in late spring and early summer.

Happy Gardening to You!

Dawn