"Bearded Iris Growing Cycles" Part 1

Finally found some of the details I was looking for. From the book "Magic of Irises" by Barbara Perry Lawton pp172-173

"Rhizomatous bearded irises should be divided every 3 to 5 years...(more often in some regions)...
Although you can dig and divide bearded irises anytime you can work the ground, the best time for transplanting is when the rhizomes have reached their maximum growth and are semi-dormant -- in July, August, and September in most parts of the US. The point is to divide the rhizomes and replant them in time for them to grow new roots during the fall months.
If you time things right, you may even have significant blooms from the new divisions next year. If you divide bearded irises in the spring, the plants will probably be fine, but you probably will sacrifice the current year's flowers.
If you divide and transplant bearded irises too late in the fall, the plants wont have time to develop new roots and become reanchored in the soil. The result may be that freeze-thaw cycles will heave them out of the ground. Knowing the growing cycles of bearded irises explains the timing of transplanting.
When the soil warms up in the spring, irises begin growing aboveground, developing this year's foliage, buds, and flowers. The roots on last year's old rhizomes decay and disappear during this period. At the same time, the new iris roots on this year's productive rhizomes are growing, supplying nutrients and water to the foliage. Once the plants have flowered, rhizome and root growth continue for about 2 months in this year's blooming rhizomes.
During this stage,nutrients are being stored in the rhizomes for the following season's growth. At this time, the rhizomes develop the new rhizomatous growing ends from which next year's foliage fans and flower buds will arise.
The growing productive parts of the rhizomes look like a Y. The leg of the Y is the older part of the rhizome and the arms are the newer parts where next year's growth will take place.
Once this growing period is over, most of the bearded irises rest until the late-summer rains arrive. The irises are semi-dormant during these weeks. The exceptions are the reblooming irises that grow continuously throughout the summer and so must constantly gather moisture and nutrients for repeated buds, stalks and flowers. The late-summer rains and slightly cooler weather trigger a new round of root growth. Extra water during hot, dry summer months will cause these irises to begin their late-season period of root growth sooner.
(To be continued...)

This message was edited Jun 26, 2006 8:49 PM

Very good info... I have noticed here that if I divide and replant early in the summer - the earlier I replant the better chance I have of bloom next season. In other words... division planted in June will have a better chance of a bloom next year..than ones planted in July/August.

Great information. Thank you. Hurry to page 2 so I can learn more. I have some 80+ hybrid Irises that I have collected over the years. Never had a problem. Even the irises I purchased from Schrieners last year bloomed beautifully this season.

Even though I know how to grow them successfully, I never knew they had a dormant period in the summer. I transplanted a few varieties last year in September last year. Needless to say, I lost a few, and the others didn't bloom. I knew I should not have waited to Sept. Never again. I may start dividing the most crowded now.

I have one question. I noticed when I planed to remove the old flower stems, a lot of them have seed capsules. I have always wanted to try hybridizing irises, now nature did it for me naturally. I am going to let the seeds ripen, then harvest them. Do you have any information on sowing iris seeds, other than they need cold stratification?

Excellent presentation. You have taken a lot of bits and pieces of info discussed on this
forum and put it in one package. Good info for all of us.

I had forgotten about this post! Yes, I can continue it, and add some information from another book related to this subject....

Oh please do,this is absolutely GREAT information.
I have just a few irises which should be dug up ,not divided but moved.So I imagine the same is true the sooner the better ?

I have participated in 3 iris co-ops so far and will have a iris bed soon.So I can share/trade in a few years :-) and repay some kindness to fellow gardeners.

I am so smitten by the beauty of iris now that I am trying my best not to loose any again.

Question once they have bloomed and I want to move them or add soil I can do it now if they have bloomed already or should I what till end of july??

I myself prefer to dig the last part of July first part of August and replant then as well allowing the new rz's time to grow and get some roots after the bloom period. I've dug some before that and the rz's were not as large nor did they have many roots so not again. My rule at least one month after blooming a bit more is better. The time varies with your zone and micro-climates.

GREAT!
Now I have a better idea of what Im Supposed to do to keep these irises happy!

if theyre happy - they'll flower more, bigger, better, etc
thus making me happy too!

Im going to put this info to work this week!
Thanks - Eagerly Awaiting Part 2!

"The probem of not knowing is
Ya' Just dont know!"

Thank you for all the infoneed to keep irises all happy !!!!

Great article here. At first I was confused(nothing new). Read it again and it makes great sense. I really needed to read this and will use the info for sure. Thanks for sharing it.

I am continuing to copy the information from this book on the new thread, "Bearded Iris Growing Cycles" Part 2.