On 08/01/2016 13:35, Michael Uplawski wrote:

Good afternoon,

In our domestic wet park (« phytoépuration »), we have combined Iris («
Iris des Marais »), Lythrum salicaria and Scirpus...

The time has come that I have to thin out the Iris for the first time,
as they have become very massive. The rule is to eliminate half of the
plants. Now I have my first encounter with the impressing rhizome of the
aquatic Iris and wonder if I can cut it in half without hurting what
remains of the plant, or if there is any best way to do that.

An alternative would be to take out all the Iris, separate them
carefully (how?) and replant just a few, but this would be quite a
chore.

Please do not respond with the recommendation to get rid of the Iris.
They are isolated from the rest of the terrain in a basin and they are a
huge success as host of water-cleaning bacteria, apart from their
beauty... ;-)


Michael



Hi Michael,

Happy New Year! I'm certainly not going to advise you to get rid of
your Iris (otherwise, and internationally, known as Iris pseudoacorus);
as I think they're excellent plants for nature. As well as helping to
clean water, they provide water-dwelling creatures with somewhere to lay
eggs, plus an escape route for larvae *and* they also attract bees.
Their beauty is certainly a bonus.

They can be divided from midsummer through to autumn, although I divided
mine about April time when the weather was warm and growth starting. You
can be fairly rough with them, indeed, you may have to be!
The hardest part for me was lifting the considerable weight of them from
my pond. As you know, they make a massive raft of solid growth, so you
may need help. I didn't need to cut my rhizomes in half because I divide
them every few years to keep on top of the job, but I'm sure it's
perfectly safe for you to cut a rhizome in two; just make sure that each
piece is healthy and has roots attached. You can then plant them
straight away where you want them to grow.

Please try and find a good home for your spare plants. I received mine
from a generous neighour, and have passed my spares on as well. Do not,
however, dump them by a river or natural wetland without permission as
they can become thuggish and detrimental to that ecosystem.

--
Spider
On high ground in SE London
Gardening on heavy clay