dividing Japanese and Siberian irises

I just learned that in order to insure blooming, one must divide bearded irises regularly. Mine are now thriving. However, is the same thing true for Siberian and Japanese irises??? Do you take from the center or the edge of the clump??? When??
Any other suggestions??
Thanks,
msmouser

Ensata Gardens - you can google it - has a lot of that sort of information on their website. They are in the Kalamazoo area, where the JI iris national convention is over the 4th of July. I've seen their gardens- marvelous.

For sibs, you can see their info and also check out irisloverdee's at Snowpeak Irises and Daylilies - she has glorious Sibs. You can also dmail irisloverdee. I've seen Dee's sibs in bloom - breathtaking!

Terry Aitken has both JI and Sib at Salmon Creek Iris Gardens. His website may have something on it for culture, though I don't recall if they do. I've seen Terry and Barbara's sibs in bloom - to die for, and have purchased some of their JI introductions.

Another place to look for info in on the American Iris Society website www.irises.org

Siberian irises do not need division as often as the bearded. As long as the clump is doing well, they are OK. When they start to die out in the middle they need to be divided. About every 4-5 years should be good. Sooner if you are intent on increasing them.

Japanese are the same. They may need to be divided a little more often than sibs. About every 3 years.

In your area early spring, when they are up about 4-6 inches is good, as is early fall. Early fall when it's not too hot, but long enough to give them 6 weeks or so to establish roots before freeze. If dividing in the fall cut the leaves back to about 4-5 inches.

Never let either of them dry out when transplanting.

Don't plant Japanese iris in the same soil where other Japanese iris have grown, or alternately you may dig the soil out and replace it. There is supposedly a harmful substance in the Japanese that causes it to poison the soil after many years.

Set the divisions so about 1 inch of the stems is underground. Mulch and water well. Do not feed until you see new growth, and then a foliar feed like Miracle Gro or Miracid, or well cooked compost only for the first year. Keep both Japanese and sibs well watered the first year, and Japanese every spring up until bloom time, thereafter. Siberians can be grown drier after the first season.

Japanese especially are heavy feeders, so after the first season some well rotted manure, or some regular fertilizer should be applied.

Sorry, I didn't see the question if you take from the center or edge of the clump.

Really whatever is easiest. I would completely dig the Japanese up, as you want the new soil. At that point you can pull it apart with your fingers if you can, or divide it into how ever many divisions you want by cutting thru it with a shovel or axe.. The larger the division the sooner it will bloom again. Siberians you can do the same, or if you want just leave it in the ground and cut chunks from it. It will grow back in within a year or so.

pollyk, you raise an issue I've not heard of before - what can you do with the soil you dig out from around/under the JI after you dig it ? Can it be used elsewhere or somehow recycled? is there anything that likes to grow in that substance it leaves behind? can it be put into a compost bin, or will it poison that too?

I don't know the answer to that.

I personally have never had a problem with the JIs. I have had some around the pond I just keep digging up and replanting for about 14 years now, with never a problem, and I believe Pirl has had JIs in the same space with no problems either. But I read in the JI bulletins or round robins about this problem, apparently it is a very big concern.

I thought it was due to my sandy soil, maybe any poison leached out, but Pirl has a heavier soil, so that's not it.

Maybe Dee could chime in, if she knows of anyone who has had problems with the JIs poisoning the soil.

I certainly would not use the soil on other irises, just in case, but I would doubt it would hurt any other perennials.

I never divide either sibs or JIs-too lazy. Haven't had any bad experiences so far (7 summers here) but we'll see. I certainly won't divide till there's a lessening of blooms!

I know that the JI Bullentins say not to plant back in the same spot but back years ago I did not know that you should not and they were planted in the same area again, no problem here what so ever.

I would think that you could recycle dirt by adding to a compost pile and letting it cook for the winter. I do not know for certain. But compost gets pretty hot around here in summer.

D

I now have about 75 varieties and getting more all the time.

I wish I had a few J Iris to divide :( I think they are beautiful! I do have sibs and rarely divide them. I usually just move a shovel full to a new location for more color. If anyone has a few to trade, please send me a Dmail.
Teresa in KY