Irises forum: My irises have stopped multiplying

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Name: Zuzu
Northern California (Zone 9a)
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zuzu
Oct 26, 2015 6:29 PM CST

Plants Admin

For years and years I had hundreds, if not thousands, of irises. Each year I would set out boxes and boxes marked "Free Irises" in front of my house because I didn't have room for all of them after I divided them. I even (shudder) threw many away.

The gophers never bothered them as long as they had roses and bulbs to eat. After I replanted all of the roses and bulbs in gopher-proof cages, however, the gophers came for the irises and ate more than half of them.

Even in the areas where the gophers have not ventured, however, my irises grow and bloom, but they don't multiply anymore. This doesn't apply only to the older clumps. The new irises don't multiply either. A few years ago, for example, I acquired lots of new irises and planted them in beds that have never been bothered by gophers for a variety of reasons. Those single irises have bloomed every year since then and still look quite healthy, but they're still single rhizomes. Not one of them has multiplied. This is true of every type of iris I grow: tall bearded, median, dwarf, Siberian, Japanese, Pacific Coast hybrid, and various species irises. What could be causing this?
Name: Mary Ann
Kentucky
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Muddymitts
Oct 26, 2015 6:32 PM CST
Boy -- that's a mystery, isn't it? I hope some of the real gurus on the list have some ideas for you, Zuzu.
Thoughts become things -- choose the good ones. ([url=www.tut.com]www.tut.com[/url])
Name: Mary Ann
Kentucky
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Muddymitts
Oct 26, 2015 6:33 PM CST
Just thinking -- is it possible that your soil is worn out? Do you add any fertilizer or amendments to the soil where the Irises are growing?
Thoughts become things -- choose the good ones. ([url=www.tut.com]www.tut.com[/url])
Name: Leslie
Durham, NC (Zone 8a)
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Lestv
Oct 26, 2015 6:35 PM CST
Well they must produce at least one new increase to keep blooming, but it is unusual that they all produce only one. Besides the gophers has anything else changed a lot in your environment? New soil? Anything?
My road calls me, lures me west, east, south & north; most roads lead men homewards, my road leads me forth. - John Masefield
Name: Zuzu
Northern California (Zone 9a)
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zuzu
Oct 26, 2015 6:41 PM CST

Plants Admin

Hi, Mary Ann. Worn-out soil is a possibility because I've been gardening intensively for 30 years in my present garden without doing much amending. I'm gardening in good sandy loam with lots of deciduous trees on the property, so I may have depended too much on the soil's ability to stay good with only the addition of the leaves from those trees. This year I did have several yards of compost delivered to my house and I spread it out fairly evenly in all parts of the garden, so maybe that will make a difference.

It's likely to be due to more than worn-out soil, however, because other plants in the same beds are performing as well as ever.
Name: Zuzu
Northern California (Zone 9a)
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zuzu
Oct 26, 2015 6:43 PM CST

Plants Admin

Hi, Les. Yes, that's the weird thing about it. They produce one, but no more.
Name: Arlyn
Whiteside County, Illinois (Zone 5a)
Irises Beekeeper Region: Illinois Celebrating Gardening: 2015
crowrita1
Oct 26, 2015 6:50 PM CST
Leslie is correct...they are making increase....they only bloom on *new* increase, and if they aren't making very MUCH increase.....do a soil test. My guess is you need a little more fertility. barring that....and if the sun *exposure* hasn't declined do to trees growing larger....my only other guess would only apply if you are using a pre emergent weed control....like Preen. If you use *too much*, it can inhibit root growth , even on established plants, and that , I would think, would cut down on increase. If the soil test shows the N-P-K to be sufficient, and the ph is right, it still *could* be trace mineral deficiency .....try using a foliar fertilizer....like Miracle Grow...they usually have some 8trace elements* not found in the bags of "10-10-10".(or whatever you use)
Name: Arlyn
Whiteside County, Illinois (Zone 5a)
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crowrita1
Oct 26, 2015 6:56 PM CST
We cross-posted ! If you have been adding tree leaves......you should be getting the trace elements you need, but, if you have been adding them to the beds "un composted", that will tie up a lot of the nitrogen in the soil (it's used in "breaking down" the leaves). I still think a soil test is in order......your county extension office can get you the particulars on getting one done, or, there are "on line" places that will do it, or, a simple test kit should be available at your local nursery, or garden center.
Name: Bonnie Sojourner
Harris Brake Lake, Arkansas (Zone 7a)
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grannysgarden
Oct 26, 2015 7:18 PM CST
I would trust your state extension service to do your soil test in their labs. They do a good job but this time of year it may be a bit of a wait for the results. Farmers have their soil tested in the fall to find out what nutrients to add over winter and during the spring soil prep. So the sooner you get the soil sample in to the lab, the better. And Arlyn is exactly right. As well as the big three, nitrogen, phosphorus and potassium, plants need three other major elements, sulfur, calcium and magnesium. They also need minute amounts of trace elements such as iron, manganese, zinc and copper in order to thrive. Everyone should have their soil tested. In my state it is free to gardeners as the farmers are taxed to pay for all soil tests done in the state. Many states do not charge or if they do charge it is a minimal fee. well worth it. Call your state extension service and ask questions. They are a great friend of the gardener.
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Name: Jane H.
Kentucky (Zone 6b)
Irises Birds Region: United States of America Region: Kentucky Clematis
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janielouy
Oct 26, 2015 7:19 PM CST
Another thing I have found is that many of the newer varieties do not increase as prolifically as some of the old historics. It does depend on the cultivar. I agree that adding amendments, compost and fertilizer does help but some just do not increase as freely as old ones.
Name: Zuzu
Northern California (Zone 9a)
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zuzu
Oct 26, 2015 7:20 PM CST

Plants Admin

Hello, Arlyn. I use no pre-emergent weed control or any other chemicals, and I don't really "add" the tree leaves. They just fall off the trees into the beds and I leave them there. I will try testing the soil, although it seems to me that any serious imbalance or deficiency would also affect the other plants (roses, clematises, alstroemerias, etc.) in the beds.
Name: Zuzu
Northern California (Zone 9a)
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zuzu
Oct 26, 2015 7:22 PM CST

Plants Admin

That's interesting, Jane. I may be expecting too much from the newer irises, but the problem is also common to the older ones. I wonder if those crafty gophers are nibbling at every increase but one. Confused
Name: Lucy
Hamilton, MA (Zone 6b)
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irisarian
Oct 26, 2015 9:33 PM CST
A friend has trouble with voles eating the roots, especially over winter.
Name: Sherry Austin
Santa Cruz, CA (Zone 9a)
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Henhouse
Oct 26, 2015 10:19 PM CST
Zuzu, I've wondered if the gophers in my garden nibble at the roots and move on to tastier things.. I've had one area where Iris should do well, but don't. They don't increase much and several have never bloomed. It's adjacent to the orchard, where gophers are around. We don't have free testing in my county. You have to send it to an independent lab.
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Name: Zuzu
Northern California (Zone 9a)
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Clematis Irises Garden Ideas: Level 2 Celebrating Gardening: 2015 Plant Identifier Garden Sages
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zuzu
Oct 26, 2015 10:54 PM CST

Plants Admin

Thanks for your input, Sherry. I'm happy to blame the gophers for any problem in my garden, and I'm usually right. Hilarious! I think they might be nibbling at them just enough to severely compromise them without killing them.
Name: Jan Wax
Mendocino County, N. CA (Zone 9a)
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janwax
Oct 27, 2015 9:16 AM CST
Zuzu, since you're in drought-stricken California, I wonder if a lack of water could be affecting them?
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Name: Richard
Joshua Tree (Zone 9a)
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creativeclover
Oct 27, 2015 9:32 AM CST
Janwax, I am in Southern CA and mine are multiply pretty good. I didn't get much blooms on some as I think its because they are too crowded.
Name: Paul
Utah (Zone 5b)
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Paul2032
Oct 27, 2015 10:51 AM CST
Zuzu......I would guess that the iris have used up the fertility in the soil that they need. Over the years I have rejuvenated several beds with good success. In two beds I dug the iris during the summer and then added lots of organic material like leaves, compost, alfalfa pellets, well aged manure and also 10-10-10 fertilizer and tilled it in. I left the beds empty til the next year. In one I planted seedlings that I had germinated during the winter. They grew like gang busters and nearly 100% bloomed the next spring. In another bed the city had to dig up a few roses to put in a new water line so I worked up the soil and planted some small leftover rhizomes. Only a couple bloomed but the rest are huge with several increase and should be top quality bloom next year. One more comment. I often see it suggested that older iris are more vigorous and grow better than the newer ones. I don't think as a general matter this is true. The older iris with the good reputations were introduced the same year as many iris that are long forgotten....survival of the fittest. I think that in 20 years some recent intros will have proved their vigor and will be widely grown and appreciated and others which didn't grow well will be forgotten.
Paul Smith Pleasant Grove, Utah
Name: Zuzu
Northern California (Zone 9a)
Forum moderator Plant Database Moderator Charter ATP Member Region: California Cat Lover Roses
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zuzu
Oct 27, 2015 1:19 PM CST

Plants Admin

Jan, I don't think the drought is to blame for this. I often worry that the irises in the same beds with roses might be getting too much water, in fact.

Paul, I'm inclined to agree with you and the other people who asked about soil fertility. This morning two more yards of compost were delivered here, so I'll apply more to all the beds and see whether it makes a difference this year.
Name: Lucy
Hamilton, MA (Zone 6b)
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irisarian
Oct 27, 2015 2:13 PM CST
yea for compost! There are irises just as old as some happy historics which didn't make the grade.

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