Irises forum: Dutch Iris - a suggestion to improve bloom and hardiness

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Sweden
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William
Jan 13, 2017 9:29 AM CST
In the bulb forum I have previously mentioned a method that can boost hardiness and bloom of the Dutch Iris. As I noted that a few members in colder zones have problems with getting repeat performance from these irises, I though I'd start a discussion here as well. Some may object that I'm in USDA 7b and should have no problems with Dutch Irises, but keep in mind that the USDA zones really aren't relevant for the Scandinavian climate. We are far north and the winters are long and the summers cold and short.

One of the problems with the Dutch Iris is that they starts to grow very early. In a mild winter this may not be much of a problem, but if the foliage is damaged in the winter, it means less energy to build a new bulb and less bloom in subsequent years. The solution to this is quite simple. They need late planting.

Plant them at the same time as tulips should be planted in your area. Wait until the soil temperature is at 10℃/50℉. Here that usually means late October or mid November, your area may differ.The idea is to give them enough time to root, but not allowing too much foliage growth.

I do the same to prevent freeze damaged on fall planted garlic. It's not a 100% certain method as if we are unlucky and the weather turns mild and warm, we could still get some foliage growth, but at least it will be less than if we plant too early.

Come spring they will need to be fertilized lightly a couple of times with a fertilizer suitable to your local conditions. Lower nitrogen numbers is usually a good thing.

Once the foliage yellows the bulbs usually need to be dug. They need warm and dry conditions as this improves winter hardiness and bloom. Moisture will stimulate early root growth. I like to stor mine in dry sand in a covered, ventilated cold frame, however in warmer areas this may prove to be too warm, so then you may need to bring the bulbs inside or in a more shady position. In all cases they should be stored away from ripening fruits and the area must be well ventilated. At this time we should also divide the bulbs as Dutch Iris reproduce like rabbits and leaving them crowded would eventually lead to declining bloom.

The downside to this method is that it's a bit more work with it and unfortunately late plantings means the bloom can be later as well. For reference, last year my Dutch Irises bloomed at the same time as my Tall Bearded. For these reasons I might not keep growing the Dutch Irises as the extra work and the late bloom is a negative for me, but the method as such has been a success so far. I have had much better bloom on my own bulbs, than I had with freshly bought stock. That said, an extra cold winter still may cause problems, so obviously I can't guarantee success.



In summary:
Plant late, at the time it's correct to plant tulips in your area.
Fertilize.
Dig and divide them annually. Store dry and warm
[Last edited by William - Jan 13, 2017 9:30 AM (+)]
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Name: Lilli
Copenhagen, Denmark, EU
Irises Roses Bulbs Hellebores Foliage Fan Cottage Gardener
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IrisLilli
Jan 14, 2017 4:29 AM CST
Thank You! I had that exact problem with mine; pre-winter foliage, frost damage and no bloom! Thumbs down
I keep mine in pots, so they are easier to move to a dry location when they are dormant, but it is a bit of extra work and I'm not sure I want to give them another try, but now I have an idea of what not to do next time! Thumbs up
You don't know if it will grow until you try!
Sweden
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William
Jan 14, 2017 5:34 AM CST
The first year I also had mine in a pot (actually a large bucket), that I placed in the cold greenhouse, as I was uncertain of how hardy they were. However I still only had around 60% bloom on them, despite that there were very little visible frost damage!

When I removed them from the pot in the summer, I noted that many of the bulbs were much larger than when I bought them. This time I planted them directly in the ground, but sorted the bulbs according to size and had 100% bloom on the larger bulbs. These bulbs in turn made even larger offsets. So I have a suspicion that some of the Dutch Iris bulbs sold are too small to flower the first year Thumbs down

Name: Lilli
Copenhagen, Denmark, EU
Irises Roses Bulbs Hellebores Foliage Fan Cottage Gardener
Plant Lover: Loves 'em all! Seed Starter Winter Sowing Bee Lover Dog Lover Region: Europe
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IrisLilli
Jan 14, 2017 6:14 AM CST
I suspect you might be right...
You don't know if it will grow until you try!
Name: Leslie
Durham, NC (Zone 8a)
Region: North Carolina Irises Cat Lover Garden Photography Enjoys or suffers hot summers Celebrating Gardening: 2015
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Lestv
Jan 16, 2017 12:52 PM CST
Mine are buried under grass. I have never thought to dig them up every year. I don't dig up my other bulb flowers either. I do get dutch iris foliage coming up in the fall that dies in the winter then comes back in the spring. It would probably help my bloom to dig them, but then I have to figures out where to store them.
My road calls me, lures me west, east, south & north; most roads lead men homewards, my road leads me forth. - John Masefield
Name: Bonnie Sojourner
Harris Brake Lake, Arkansas (Zone 7a)
Magnolia zone
Region: United States of America Region: Arkansas Master Gardener: Arkansas Irises Plant and/or Seed Trader Moon Gardener
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grannysgarden
Jan 16, 2017 1:37 PM CST
I don't dig mine either. I have stopped digging up plants in the fall to replant in the spring. Mine keep coming back and they bloom each spring. I have purple, yellow and yellow and white tall ones and then several of the smaller varieties like Lion King and Miss Saigon.
Who plants a seed beneath the sod and waits for growth believes in God. ~~Unknown
Sweden
Bulbs Lilies Bee Lover Irises Hellebores Deer
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William
Jan 16, 2017 3:13 PM CST
I had the impression that most that have problems with Dutch Irises are in USDA zone 6 or colder or are in a less favorable area, such as my own, so I find it interesting that you still have your foliage dying back in the winter, Leslie. I guess that even with dieback the bulbs would have more time to replenishing their energy for next season in a warmer climate, so the impact of foliage loss could still be less than in a colder zone.
Name: Leslie
Durham, NC (Zone 8a)
Region: North Carolina Irises Cat Lover Garden Photography Enjoys or suffers hot summers Celebrating Gardening: 2015
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Lestv
Jan 17, 2017 2:06 PM CST
It is problematic for bulbs in my area. After a very hot summer, fall must be just cool enough to send the iris out of dormancy. We can have very mild winters, so the foliage that has already grown from fall gets done in by a stretch of snow or ice, and then starts over. They are pretty rapid with their later growth, from say February to March, since they bloom by late March, early April. My poor neglected Dutch iris having been coming back and blooming for at least 15 years or so.
My road calls me, lures me west, east, south & north; most roads lead men homewards, my road leads me forth. - John Masefield
Sweden
Bulbs Lilies Bee Lover Irises Hellebores Deer
Celebrating Gardening: 2015 Photo Contest Winner: 2016
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William
Jan 17, 2017 3:35 PM CST
Dutch Iris do need a warm summer (or dry, warm storage, sometimes referred to as "baking") to be able to bloom properly, so I would say that at least in this case the hot summers work at your advantage, Leslie Smiling .

In contrast Dutch Iris don't bloom before June in my garden. I do wish they had bloomed a bit earlier.


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