Irises forum: How Large should a clump get ?

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Name: Patrick
Toms River, New Jersey (Zone 7a)
Dog Lover Irises Orchids Region: New Jersey Region: Pennsylvania Lilies
Jul 20, 2015 4:11 AM CST
I've seen some photo's here on the forum of some rather large clumps of iris. The visual effect is stunning, but I'm wondering how large should you let them get before you start to divide up the clump ?
Name: Tom
Southern Wisconsin (Zone 5b)
Irises Vegetable Grower Butterflies Region: Wisconsin Keeps Horses Cat Lover
Dog Lover Keeper of Poultry Daylilies Celebrating Gardening: 2015
Jul 20, 2015 6:30 AM CST
If the rhizomes start to grow over the top of each other, they will need to be thinned. Thinning some out every year allows you to maintain a clump for a quite a while without actually dividing it. When you divide, you can replant several of the same kind to give the same appearance of a large clump. Each cultivar seems to have it's own way of growing, and some just seem to grow nice and don't get too crowded for a long time, others seem to grow all over themselves and need thinning more often. So the answer to your question is "It depends on the individual iris" and your preference to how large an area you want covered with one kind of iris. Smiling
I am not afraid of an army of lions led by a sheep; I am afraid of an army of sheep led by a lion. - Alexander the Great

Jul 20, 2015 6:43 AM CST
Good advice, Tom. I planted several rhizomes of Ocelot in a circle, with the growing side out, and every year since I have added soil around the clump and kind of levered up the outside of the clump so the rhizome was back on a level instead of going down the slope. Occasionally I cut out a section with a knife if I see one area is getting too crowded and plant it elsewhere. I think this is a winning method for me.
Name: Lee-Roy
Bilzen, Belgium (Zone 8a)
Irises Lilies Hostas Ferns Composter Region: Belgium
Jul 20, 2015 8:09 AM CST
Depends on the kind of Iris you're referring to. Rhizomatous iris like germanica need to be divided much earlier than let's say sibirica because the inside gets congested/old and because of that don't produce blooms anymore.
Germanica needs to be divided every 3-5 years while sibirica can last up to 10 I've heard.

General rule is if the flowering decreases: divide
Name: Dee Stewart
Willamette Valley OR
Snowpeak Iris
Forum moderator Charter ATP Member Hosted a Not-A-Raffle-Raffle I was one of the first 300 contributors to the plant database! Region: United States of America Region: Pacific Northwest
Hummingbirder Garden Art Birds Dog Lover Cat Lover Region: Oregon
Jul 20, 2015 8:11 AM CST


most commercial growers divide yearly for better crop, my home ones divide every 3 years.

Denise Stewart
Snowpeak <url></http>

Name: Mary Ann
I was one of the first 300 contributors to the plant database! Region: United States of America Hostas Hummingbirder Daylilies Birds
Irises Keeps Horses Region: Kentucky Farmer Container Gardener Celebrating Gardening: 2015
Jul 20, 2015 8:13 AM CST
Yes -- you're referring to Tall Beardeds and Dwarfs, right Dee? I divide at about the three-year mark too. I will try to postpone to four-year if I can.
Thoughts become things -- choose the good ones. (

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