Beauty and the Beast - Questions on Iris care

I am slowly realizing that growing irises is more complex than I had thought. (Except for the old faithfuls that have grown here for years without care.) Last fall is the first year that I dug, divided, and cut back many irises, looking for iris borer. (Yes, they were there!) Now this year I realize that I planted different varieties too close together, when I first planted them several years ago, and now that they are finally blooming this year, they have all grown together and need the above treatment, but once the bloom is over I won't be able to tell where one variety begins and another ends...
So what should I have done? Start out by planting each separate rhizome 2 feet apart? What to do with all the ground in between? Or maybe start them out closer together, and every fall move every other clump so there is more space? Is later better for moving and de-borering? Is there any hope of bloom next year if I divide them, or do I have to wait several years until they clump up? Guess I need to read a textbook to answer all my questions!
Sharon

The earlier in the year you do your digging and dividing, the better. Conventional wisdom has always been to wait 6-8 weeks after bloom before dividing to give the increases time to mature, but that wisdom does not work to the benefit of folks in cold-winter climates. We in the cold zones need to get our irises in the ground as early in the summer as possible to give them time to root in and establish before winter. Fall planting of bearded irises in the cold zones is risky business.

Early dividing and planting is also beneficial in terms of borer control. If you catch the borers in the rhizomes before they leave to pupate in the surrounding soil, you can cut them out and dispose of them when you divide the clumps and clean up the rzs. You can also treat any secondary rot infections in the rzs before they destroy your irises.

Also, the earlier you get the irises divided and replanted, the better your chance of getting bloom the next spring. Irises don't have to clump up before they'll bloom. They just have to have a decently established root system and at least one mature, blooming size rz.

If you don't want to have to dig and divide every year or every other year, plant your taller medians and talls at 2' spacings. MDBs and SDBs can be planted 1' apart. Most bearded irises require dividing every 3-4 yrs even if they aren't growing into their neighbors. Even a single clump can become overcrowded and lose blooming vigor after several years. I wouldn't recommend digging every other clump every year because you'll never get any large, mature clumps with multiple blooming stalks. Irises just don't clump up as quickly in the short-season Midwest as they do out on the West Coast where iris gardens are dug and divided every year.

You really don't want to fill the spaces between irises with other plants because good air circulation is essential to iris leaf and rhizome health.

Laurie

Laurie,
Thank you so much for your condensed and experienced information on iris care. I'm glad you say that earlier is better, because that is just what I am itching to do!

If I were to dig up just part of a clump of irises (any that are healthy looking) and divide and replant the parts I dig, would that be a way to ensure that there would likely be some in bloom every year? (In other words, leave two thirds of the clump alone. Kind of a rotational division. )

Fot this early digging and dividing, do you still dip in bleach water, and let the rhizomes dry, or just replant? Cut back foliage?
Garden Blessings,
Sharon

Sharon,

Digging and dividing partial clumps is one way of making sure you have at least part of an undisturbed, established clump to hopefully bloom every year, but I think a better strategy is to plant at least two clumps of each cv so that you can divide one clump a year and leave the other(s) untouched. If you leave partial clumps, eventually even those partials will accummulate old dead rzs; overcrowded viable rzs; and will deplete their surrounding soil of essential nutrients. It's best to dig the entire clump so that you can remove the dead rzs, check the health of the remaining ones, and amend the soil properly before replanting.

I don't bleach irises being replanted into my own garden unless they have a specific problem I'm trying to treat like borer damage, rot, or aphid infestations. Usually I just shake off the old dirt, divide, do a quick visual check for any problems, cut back leaves just enough so they aren't top heavy, and replant.

Laurie

Do you mean BUY two plants, or divide as soon as there is more than 1 rhizome?
(Sorry for being such a pest - but it is SO nice to have an expert available at the click of a mouse!)

Thank you truly and greatly,
Sharon

You were asking about dividing clumps, which would imply that you already have more than 1 rz of the irises in question. When it becomes necessary to divide the original clump, replant at least two divisions (either single rzs or small clumps) so you will have two or more clumps that you can then put into a rotational dividing schedule as they mature and need dividing again.

Another tactic I have used here just because my beds are soooooo crowded is to plant 2-4 rzs of the same cv at half the spacing I would use for different cvs. In other words, I plant a row of 4 Immortality rzs at 1' spacings followed by a 2' gap and then another 4 rzs of Superstition at 1' spacings. It really doesn't matter if the Immortality clumps grow into each other or if the Superstition clumps grow into each other, but I don't want Immortality growing into Superstition. That works easiest if the bed is planted in rows as mine all are.

Laurie