Monday, April 4, 2011

The Iris That Ate The Pond

Nearly every iris we grow needs digging and dividing every few years. There are a few exceptions, siberians only need dividing if they slow in flower production, spurias almost never need division. There is one iris that is so good at self sowing it seems pointless to divide, Iris pseudacorus. Grown in poor dry soil it can behave like a dwarf iris and is shy to flower or set seed. However, if it is growing in moist soil it can be extremely vigorous and produce copious quantities of seed. When it is in its prime habitat of shallow water it becomes a thug. It can seed over an immense area crowding out nearly every other plant. It is happy in anything from moist soil to nearly two feet deep in water.
I foolishly planted a few select Iris pseudacorus in a pond about twenty years ago. A couple white flowered ones, a yellow with extra large flowers, and a giant form. I had previously planted a pseudacorus with variegated leaves that was eaten by muskrats. I assumed the green leaved forms might be just a tasty and did not actually expect them to survive predation by the pond's resident muskrat family.
Not only did they survive they thrived. I suspect the muskrats are farming the Iris pseudacorus. The pond is a glorious sight in Spring covered in golden flowers with an occasional white flower still making an appearance.
The sad part is, I was warned. Nearly everything I had read cautioned against planting Iris pseudacorus near water. So, even if you have the knowledge it is worthless unless applied.
I do not want to discourage anyone from growing the cultivars of Iris pseudacorus in the garden as there are many wonderful selections available. There are also some really cool hybrids that do not set seed and would be perfect at the edge of a pond or lake.


  1. On the positive side if you plant it in a swamp in a few years time you'll have dry land instead of water...if you need to get rid of a wwamo that's the plant for it!...

  2. I disagree with your statement that you "do not want to discourage anyone from growing the cultivars of Iris pseudacorus in the garden ..." Despite your assertion that it can be managed, you only have to become inattentive for a season or two to risk it escaping and establishing itself in a wetland area. The plant is offered for sale every year in nurseries and big box stores throughout the country. Additionally it’s vibrant color and sturdy foliage makes it a favorite with landscapers. Anyone who spends time in wetland areas where the plant has managed to get a foothold can tell you that its habit qualifies it perfectly as an invasive species. 1) It produces large numbers of new plants each season 2) It tolerates many soil types and weather conditions 3) It spread easily and efficiently, usually by wind, water, or animals 4) They grow rapidly, allowing them to displace slower growing plants, and 5) they spread rampantly when they are free of the natural checks and balances found in their native range. Please see the USDA plant profile for Iris pseudocorus and the Invasive Plant Atlas
    In Louisiana it is overtaking our native species. If we didn’t already have a problem with loss of natural habitat for our native irises, the introduction of pseudocorus to the wetlands is crowding out the remaining stands. This is becoming a comparable situation to the lovely Purple Loosestrife Lythrum salicaria which created such a problem for other wetland areas.
    Unless we can guarantee that every seed pod will be removed and destroyed, or rendered sterile, there is no justification for encouraging it further distribution.

  3. It is an attractive plant, but note that several states have banned it or otherwise listed it to limit its use (compiled by the University of Florida):

    Iris pseudacorus
    Connecticut: Invasive, banned
    Massachusetts: Prohibited
    Montana: Category 3 noxious weed
    New Hampshire: Prohibited invasive species
    Oregon: "B" designated weed, quarantine
    Washington: Class C noxious weed

  4. Beautiful photo. Hopefully the seeds won't wander further.

  5. Can they be contained in a small area, container, etc.? Like a bucket or bigger.