Karen Mullen wrote:

I bot sweet flag for the first time and was wondering... it needs replanting,
should I do it now before winter or wait til spring. Also, should it be cut
down to the soil when cold sets in or leave it's stalk after they've died until
new growth appears in spring. And does the same apply to water iris.

Karen
Zone 5
Ashland, OH

We're in a slightly warmer zone (USDA Zone 7) so our experience with
these plants may not be the same. Our sweet flag doesn't die back in the
winter, even when we've had snow and ice. If I want to divide it, I cut
it with a sharp knife or shovel into 3-4 pieces and repot in early
spring. At the same time, I cut last year's foliage back. When I don't,
it tends to get ragged and sometimes borers (plant pest) overwinter in
the old foliage. (By the way, green lacewings are great natural predator
for borers, spit bugs, aphids and soft scale.)

The water iris dies back in the fall. I pull off or cut the old foliage.
This I also divide in the spring; just remove old rhizomes and replant
4-5 new sections per 5 gallon pot.

I plant all our pond plants in lava rock or river rock that is 1-3
inches diameter, then top with 3-6 inch rocks to keep the koi out of the
pot (they'll suck out the 1-3 inch rocks and empty a pot within a few
days!!)
--
Zk (sig compliments of BV)
3500gal pond, 13 pond piggies
Oregon, USDA Zone 7