By Patrick O'Connor
If there’s anything that is generally understood about
Louisiana irises it is that they like water.
As these irises have risen from obscurity to popularity among gardeners,
however, their promoters have had to walk a fine line in describing their water
needs.
On the one hand, it has been important to convince people that
these “swamp plants” do not have to grow in standing water. Gardeners can succeed quite well with them in
a bed alongside annuals and perennials of many kinds. On the other, optimal performance may not be
attained if their Louisiana irises get only the amount of water that the
“average” plant needs.
Louisianas suffer if they get too dry, even for a brief
period. They require consistent
moisture. If they dry out during
an even brief drought, especially from spring through summer, they will begin
to have scruffy foliage and, in the extreme, go essentially dormant. Generally, with insufficient water, they
enter an in-between state in which much of the foliage is just yellowed and
unattractive. This is hardly a fatal
condition, but it is not a pleasing sight.
Ample water is the preventative.
(Soil fertility is also critical, but that is mostly another story).
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| The thirstiest Louisiana, Iris giganticaerulea, in a swamp in Jean Lafitte, LA. |
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| I. brevicaulis, the least thirsty of the species, growing in Gary Babin's Baton Rouge backyard, nowhere near standing water. |
Different Louisiana irises may have a greater or lesser
tolerance for insufficient moisture. In
a separate series of blogs, Joe Musacchia is describing the background and characteristics
of the species that are the foundation of today’s cultivars. For present purposes, it is enough to say
that some of the species (
Iris
giganticaerulea and
I. nelsonii)
are indeed swamp dwellers, found growing in standing water. (The East Coast species
I. hexagona appears to like the same or similar conditions as
I. giganticaerulea, but this iris has
been used only rarely in developing the modern cultivars.) At the other extreme,
I. brevicaulis is an inhabitant of low, damp spots, but is not
generally found in anything beyond the mucky edges of water.
I.
fulva is intermediate in this regard, often the inhabitant of wet ditches
and sloughs that may hold water all or most of the year. The water requirements of a cultivar will
depend upon the often obscure or unknown genetic mix of these species in its
background.
The issue is how to deal with the water needs of Louisiana
irises so that they are respectable citizens of the garden when not in bloom,
as well as how to encourage plentiful and beautiful flowers. There are any number of approaches that will
work so long as the result is that the irises remain consistently wet. One could drag out a hose and attend to their
thirsty cravings by hand watering. Not
many of us would elect that course, at least for very long. I once used a sprinkler placed around the
garden on a rotating basis, but even that got old, and I was not really as
consistent as necessary. I had reasoned
that in the New Orleans area where there are 60 inches of rainfall annually and
where the irises are native, it should not be necessary to take herculean steps
to water these plants. I was wrong, and
I was never satisfied with the way my irises looked in the hot summer months.
A switch to a series of sprinklers each on a timer was a
huge improvement. That arrangement
created the consistency of moisture that the irises require, and for the first
time, the foliage on my irises remained green and attractive right through the
summer heat. Only in the fall when the
new growth cycle began did I have to apply serious work to clean up the iris
foliage.
The weeds responded well to this approach also. I found it difficult to keep up with the
weeding, especially with some noxious non-native perennials, such as alligator
weed.
When I operated a nursery, Zydeco Louisiana Iris Garden, I
had grown many plants in half barrels with no drain holes. That worked well generally, but most of those
barrels were at another location, not in my home garden. My primary objective at home has been to
maintain an attractive landscape and not have it look like a production farm,
even though I did use much of the yard space for nursery operations. I was in the market for water-holding containers
without an industrial appearance.
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| A mortar mixing tub from Home Depot, a future home for Louisiana irises. |
The solution came to me in an email from Wayland
Rudkin. A California hybridizer, Wayland
sent me a picture of his ‘Ginny’s Choice’, later a Debaillon Award winner,
growing in a shallow tub of the kind
sold in the construction sections at Home Depot and Lowe’s for mixing mortar. The tub in Wayland’s picture was packed with
happy, healthy looking irises.
These mixing tubs are sold in two sizes, one about six
inches deep that measures 18 by 24 inches and the other two inches deeper and
slightly longer and wider. There are no
drain holes. The smaller size sells for
between six and seven dollars and the larger between twelve and thirteen
dollars. They are black and made of some
sort of thick plastic material. They
will crack if hit hard, stepped on, or lifted while full of soil, but they otherwise
seem sturdy and probably are reasonably long lasting. These trays can be sunk into the ground or
placed on the surface.
I opted for the smaller, shallower tubs for reasons of
economy and to maximize the number of cultivars I can grow. I have replaced most of my iris beds with
these mixing tubs set one next to the other on the soil surface or on
landscape fabric in a few areas. The
rims of the tubs can be overlapped to prevent weeds from growing between them. I have found that the tubs currently sold by
Home Depot work better for overlapping than the ones from Lowe’s because of a
flatter rim. The tubs can be angled
slightly to accommodate curved beds or walkways.
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| Mixing tubs in place but not yet mulched. |
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| A garden path with tubs cleverly disguised by rows of bricks and Live Oak leaf mulch. |
If the tubs are not dug into the soil, it is necessary to
resort to camouflage for an unobtrusive look.
In my case, I lined the paths in my garden with bricks stacked two or
three high. When mulch is added and the
irises are growing well, the tubs are essentially hidden, and the look, to me,
appears natural.
After two and a half years, I consider growing Louisiana
irises in these tubs to be a successful experiment. The irises so far have grown very well and
bloomed beautifully. Like irises in
beds, I anticipate that the tubs will have to be reworked periodically. The soil undoubtedly will have to be
replenished, although I have added an inch or so each year. Either there is a bit of subsidence or some
soil washes out, but in either case I try to keep the soil level near the top
in order to allow maximum room for root development and to prevent too much
standing water. If the trays are full or
nearly full of soil, evaporation quickly takes care of any surface moisture
that might attract mosquitoes.
I did worry when I began using the mixing tubs that six
inches of soil would not be sufficient for good growth of the irises. I have found only a few varieties with roots
so long that they hit the bottom of the tubs and then flatten across the
bottom. Even with those, the irises
appear to grow happily. Except for cost,
I probably would have opted for tubs two inches deeper, but I have not detected
any problem with the shallower model.
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| Garden scenes during the first and second seasons with the tubs in place. |
I will not go so far as to say that weeding has become a delight,
but it is much easier to pluck a weed from a mucky bog than from garden
soil. Many common weeds do not like the
bogs, although one can expect a few new ones to appear. The iris bogs are no replacement for
diligence, though, and they will look bad if unattended. Of course, any perennial weeds growing
beneath the tubs will be entirely frustrated.
This gives me great pleasure.
A bog replacement for normal beds does not require a
landscape of uninterrupted Louisiana irises.
There are many interesting plants not often found in the garden that can
be grown in the tubs with the irises.
Marsh Fern (Thelypteris palustris)
and various forms of papyrus thrive under these conditions. I devote one entire tub to a
Royal Fern (Osmunda regalis), which provides great
texture that contrasts nicely with iris foliage.
Pickerel Weed (Pontederia cordata) has beautiful blue-purple flowers and also a
nice contrast of foliage texture. The
deep red foliage of the hybrid
Crinum‘Menehune’, Red Bog Lily, is a wonderful accent, also. The use of little bogs for irises opens up a
new palette of companion plants.
There are some issues that must be dealt with if employing
bog culture. I have found a few
cultivars that do not thrive in the tubs.
These seem prefer a good garden bed but with ample moisture. There are not many, however, and trial and
error is the only way I know of to discover this preference.
The shallow tubs will dry out quickly if not watered. I had thought that this approach would be a
better way to reduce the amount of water I use.
That has not been the case. When
I apply water, however, the irises get to grow in boggy conditions, and almost
all varieties thrive year round.
I have never been sure how to fertilize irises grown in
containers that do not drain. Fertilization
is the second key to success with Louisianas.
All the fertilizer rate recommendations assume beds or containers
through which water drains rather than accumulates. I have no idea what happens with the
chemistry in those tubs. I have used
mainly time release fertilizers applied as if the tubs were containers with
drain holes. It has seemed to work, but
I am sure there is a much more refined and informed approach that would be
preferable. I suppose a container system
would be better that more closely emulated a real bog in which there is some
natural, albeit very slow, movement of water.
There are many other approaches through which the thirst of
Louisiana irises can be satisfied. For
example, Benny Trahan in Slidell, Louisiana, creates “iris paddies”, which
essentially are retention ponds with a few inches of water into which he places
potted irises. The plants are able to
suck up as much water as they want. Eileen
Hollander in New Orleans is also using mixing tubs, and has written an account
of her experience in the Spring 2014 issue of SLI’s publication
Fleur de Lis. Robert Treadway, from Carlisle, Arkansas,
wrote of his development of plastic lined beds in an article that can be found
on the SLI website at:
Development of Plastic Lined Beds
While I regard the creation of iris bogs using mixing tubs to be a
successful experiment, it undoubtedly is not one that should be tried without
modification in all parts of the country.
The weather in, say, Montana, may argue for a different approach. But a
key to success with Louisiana irises is water, regardless of how it is
delivered.
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