Monday, July 13, 2015

Satisfying Louisiana Irises’ Craving for Water

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).

The thirstiest Louisiana, Iris giganticaerulea, in a swamp in Jean Lafitte, LA.
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.
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. 

Mixing tubs in place but not yet mulched.
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.

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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