Irises forum→Iris ensata: decline?

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Name: Lee-Roy
Bilzen, Belgium (Zone 8a)
Irises Lilies Hostas Ferns Composter Region: Belgium
Lover of wildlife (Black bear badge) Region: Europe
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Arico
Jun 6, 2020 5:36 PM CST
My iris ensata seem to be declining this year. Last year and the year before that two of them were humongous, very healthy and put on a dazzling floral show as shown in this picture from 2018 (2019 was even better flowering wize):

Thumb of 2020-06-06/Arico/a292f1

This year they're only half as tall, with fewer buds and the flowering stems are also very low. The foliage is also quite bleak (not as vibrant as last year) and alot of brown leaf tops too.
Is it because I haven't divided them since I got them (three years)? Or because of the unusually wet februari (6 weeks of non stop rain) and consecutively dry spring (no rain in march or april with temps well above 20°C for alot of days). I did irrigate them deeply on a few occasions during this dry spell.
Or perhaps the constant nuisance of a mole that has taken up residence in my flower bed, making hills everywhere it can despite my best efforts to capture it? (it has come up right against the crown of the one pictured above; with THREE hills!! THREE!!) Grumbling Grumbling

(I'll try to upload a picture tomorrow of their current state)

Cultivation info: zone 8a, oceanic climate, sandy loam with pH 5.6 (though I doubt this is the problem since there weren't any in the previous seasons....)

Edit: As promised pictures of this year:


Thumb of 2020-06-08/Arico/79e897
Thumb of 2020-06-08/Arico/b42448

[Last edited by Arico - Jun 8, 2020 11:02 AM (+)]
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Name: Tienito
Rhode Island (Zone 6b)
Irises Amaryllis Native Plants and Wildflowers
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Tienito
Jun 6, 2020 6:47 PM CST
I'm no expert, but don't think that early rain is the problem, and your soil's pH would be just right for JIs. JI rhizomes grow UP, so it could be that they're too high in or out of the ground now. I would divide that clump, reset it to its original depth, and it should grow vigorously again. The clump does look congested to me.
Name: daphne
san diego county, ca (Zone 10a)
Million Pollinator Garden Challenge
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shizen
Jun 6, 2020 9:00 PM CST
i was told by some one 50 yr. ago that besides dividing, if the ji's are grown in the same spot year-after-year, the soil needs to taken out and replenished with fertile new soil. they are also heavy feeders so the need lots of nutrients, don't like to stand in water during the winter, and prefer it on the acidic side.

the advice has proven helpful to me where i had mostly clay soil. but, we've moved to an area that's hotter with sandy soil, so i am still experimenting. the first 6 years i grew them successfully in large pots, but it got to be a pain dividing and repotting every year. so three years ago i stuck them in the ground. the ji's bloom larger, but do not increase as well. jury's still out on the conclusion to the experiment. Shrug!

they'll be blooming in a few weeks, so i'll be posting pictures soon.
Name: Tienito
Rhode Island (Zone 6b)
Irises Amaryllis Native Plants and Wildflowers
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Tienito
Jun 6, 2020 9:55 PM CST
Daphne, that is so interesting. I'm new to JIs. Except for Dewa Banri, last year they didn't do much for me in the ground, so in the fall I potted them up and sank them into my veggie bed. This spring I took the pots out and put them in plastic trays that I keep filled with water. The plants seem much happier and are loaded with buds. I can't for them to bloom, to see how the flowers shake out. I also hate the thought of dividing them each year, but they seem so much happier growing this way. It's too hard for me to keep them happy in the ground.
Name: Lee-Roy
Bilzen, Belgium (Zone 8a)
Irises Lilies Hostas Ferns Composter Region: Belgium
Lover of wildlife (Black bear badge) Region: Europe
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Arico
Jun 7, 2020 5:30 AM CST
shizen said:i was told by some one 50 yr. ago that besides dividing, if the ji's are grown in the same spot year-after-year, the soil needs to taken out and replenished with fertile new soil. they are also heavy feeders so the need lots of nutrients, don't like to stand in water during the winter, and prefer it on the acidic side.


Why would you need to replace the soil? This doesn't happen in nature either.. Shrug! Besides, if you mulch anually, the fertility stays constand and the OM will increase.
central ohio (Zone 5b)
PlantingOaks
Jun 7, 2020 5:39 AM CST
I think I've heard in nature they live in delta areas that are constantly getting buried in new soil washed in from upstream. Hence why you have to keep re-burying them. That would also import fertility, yes? But don't look at me for garden advice, I haven't actually kept any alive yet.
Name: Arlyn
Whiteside County, Illinois (Zone 5a)
Irises Beekeeper Region: Illinois Celebrating Gardening: 2015
crowrita1
Jun 7, 2020 7:07 AM CST
I'm certainly no expert in beardless culture, either, but, mine are grown in sandy loam soil (amended pretty heavily at planting time with "peat soil',and "river muck") , mulched with "pine straw" (which helps bring the ph in line, although I still need to add quite a bit of sulfer). I do twice-yearly soil tests for ph, but don't check for nutrients or trace minerals. The pine needles (I think) add quite a bit of organic matter, and trace minerals , as they break down (all stalks and foliage are removed from the plants at the end of the season, and disposed of), and the "new, organic soil" being created "helps" to keep them at the correct depth, and also ties up a lot of nitrogen, while "breaking down"...so I fertilize , quite heavily, twice a year (home made mix of "about" 15-8-4). With "irrigation"..."water out of the hose", vs. 'water that came down the creek", you're more apt to be "nutrient shy", as well as getting the "buffer" ph out of whack, so you need to stay on top of your soil tests, and amendments......with lots of rain, or irrigation, you'll get more "nutrient leaching", so, again, more frequent feeding and amending for ph will probably be needed, as well as seeing if the trace minerals,,,iron, especially ...are sufficient. As to division....mine are starting to show the need for some ! They have been in place 8 years, with the only "division" being the "stealing" of some for sharing!...But, when I do that, I try to "replant" a small chunk to the "inside" (the "bare spot"!), but that is only "delaying the issue " Rolling my eyes. ! Since our soil is so "naturally sandy> and doesn't hold water well, when I "built" the bed, the JI's area was excavated to about 2 feet deep, and a layer of rubber roof membrane was laid out, then the trench was refilled with the "peat, sand, river muck" mix....that gives a barrier to stop the moisture from "leaching down"...the mulch helps keep it from "moving up", so maintain the soil moisture ids much easier.
Name: Leslie
Durham, NC (Zone 8a)
Region: North Carolina Irises Cat Lover Garden Photography Enjoys or suffers hot summers Peonies
Celebrating Gardening: 2015
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Lestv
Jun 7, 2020 9:44 PM CST
Their peak bloom is usually 2 to 3 years after planting. Once they get crowded the bloom will diminish and it is time to dig them up, separate them and replant. Unlike most all other iris Japanese Iris must be replanted in new soil. They deposit secretions into the soil that would retard their growth if planted back in the same spot. You will need to either replant them in a new spot or replace all the soil. I find replanting in a new spot easier. Other iris, beardless or bearded, can be planted in the JI's old location with no ill effects.
"The chimera is a one time happenstance event where the plant has a senior moment and forgets what it is doing." - Paul Black
Name: Tienito
Rhode Island (Zone 6b)
Irises Amaryllis Native Plants and Wildflowers
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Tienito
Jun 8, 2020 10:43 AM CST
Leslie, ditto your advice about dividing JIs. I've seen numerous reliable sources, though, that specifically call out the idea that they secrete some kind of substance into the soil as a myth. People guessed that because they didn't understand the growth pattern of JI rhizomes. Also, JIs are commonly grown in pots, where nutrients are quickly depleted, necessitating that the soil be changed. As long you amend the soil with compost and reset the rhizomes at the right depth, there's no need to move your JIs to another spot. It's only the availability of nutrients and the right planting depth that you need to provide for.
Name: Lee-Roy
Bilzen, Belgium (Zone 8a)
Irises Lilies Hostas Ferns Composter Region: Belgium
Lover of wildlife (Black bear badge) Region: Europe
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Arico
Jun 8, 2020 10:52 AM CST
I also find it hard to believe that JI's (or any other organism for that fact) needs to move because of the substances they exude into the soil (alot of plants do actually to aid in mineral uptake or as defence against pathogens)

But here are the pics:


Thumb of 2020-06-08/Arico/71228f
Thumb of 2020-06-08/Arico/b318a6

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