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With the help of this question I identified that I have Dutch Iris (Iris X hollandica) in my garden.

As described there the plants came out last autumn (we had a quite warm and dry autumn, following a super-dry spring in the same year). Over the winter the long thin leaves which came out survived (coldest day was -15 C) then some weeks ago some of the plants (6 of ~25) produced a stem where now the flower can be admired.

I have a couple of questions regarding the handling of these:

1) Is it normal that they already come out in autumn? Can I cut those ugly/partially dead leaves in early spring/late winter? (see picture below (taken in autumn))

2) What can I do to encourage more flowering?

3) When is the right time to multiply the plants (dig out the bulbs, stocking them, splitting them)? When do I need to put them back into the soil?

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up vote 2 down vote accepted

Okay, here is my answer:

1) Yes it is normal. They often even stay above ground year round. Any dead or completely yellowed foliage can be removed at any time.

2) Splitting the clump and replanting in rich, well drained topsoil will encourage flowering. Try not to compact the soil, or let it become waterlogged. Also, I've found that mulching with any carbonaceous organic material keeps out weeds better than cultivation, and is good for the plant.

3) The best time of year to divide this is in autumn before the ground freezes, but after the plant has finished with its growth for the year. This gives it time to regrow damaged roots and get established before blooming time next year.

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thanks for your answer. However the Dutch Iris does not have not a clump (I assume you mean a Rhizome), but is bulb-based. Will it produce daughter-bulbs? –  Patrick B. Apr 24 '12 at 5:58
    
@PatrickB. A clump of rhisomes. –  jmusser Apr 25 '12 at 1:47
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