Thank you to the Society for Louisiana Irises for their notes on cultivation: visit www.louisianas.org for more infomation. We have found their book : The Louisiana Iris: The Taming of a Native American Wildflower excellent and very useful.
Louisiana irises need moisture and can be grown standing in water or in a bog garden or even in ordinary garden situations. They will flower best if not allowed to dry out and need at least 2cms of water per week during the growing season. Like most irises, Louisianas need as much sunlight as possible to bloom best. They will tolerate a wide range of soil types and need a medium high in organic matter and regular feeding with a balanced fertiliser such as 15-15-15 twice a year. Louisianas are heavy feeders! Mulching is import to retain moisture, pine needles, homemade compost or horse manure would be ideal.
We made a bog garden by digging out 50cms of ground, lining with black plastic and filling with a rich mixture of soil. We have experienced a slight problem with chlorosis which was easily remedied with an iron feed. These irises are very vigorous given the right conditions, the rhizomes are very long and each plant can need up to 1sq. metre - we did not take this into account and this autumn will have to dig out the whole lot to split and replant! They clearly will need transplanting and spliting regularly!
Planting: The rhizomes should be planted just below soil level and not allowed to dry out until they have established. New rhizomes can be held for a few weeks in water with a little fertiliser, keeping the leaves high so they can take in oxygen. Louisianas can also be grown in large, wide pots submerged in a pond. Care should be taken with feeding if there are fish in the pond.
We are going to experiment over the next year by planting in different situations to watch how they perform with less water, so we can better advise. At the moment we are learning too! The Society for Louisiana irises is an excellent information source.
If you are lucky enough to have irrigation water and/or damp situations, we strongly recommend growing Louisianas. You will be rewarded by a stunning display of colours!
Louisianas will flower at the same time as the Tall Bearded irises, for us that is early May.