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Louisiana irises have unique cultural requirements that apply in most of their growing range, with adaptation for climate and growing conditions.
Ideal growing conditions have a lot to do with the soil acidity and, if in a cold climate, protection during the winter. These irises do not like high alkalinity or excessive acidity, even if wet. The ideal pH range is 6.5 to 7.2, slight acidity to slight alkalinity. At times, people have thought that Louisiana irises needed acidic soil, because some species like I. fulva grow in river deltas or swamps. But this is not the case, which is good news for many gardeners because soil pH can be adjusted. As far as cold climates are concerned, Louisiana irises require mulch and/or snow cover. If the ground freezes and they are not protected, they will not survive into spring. Finally, for those growing in dry areas such as in the southwest, Louisiana irises can be grown in water gardens or under water culture, even if not in the native soil.
Louisiana irises need not be grown in water or under bog conditions, although they do well in both environments. However, there are additional options. They can grow directly in the soil, in containers, in large tubs, in raised beds, and in big barrels or irrigation tanks. Some gardeners experiment with large cement mixing tub containers (with a varied combination of soil and mulch materials) that do not drain. Also, since all irises vegetatively reproduce, consider the space constraints of the location you choose so that the irises have room to grow. For instance, a very small container that is just big enough for one rhizome will not provide room for the iris to reproduce.
Louisiana irises like sunlight. Plant them in areas where they get at least a half day of sun. Dappled sunlight provided by a very tall tree canopy can provide enough sunlight and needed shade in the summer. However, irises do not like to grow directly under trees where they must compete with the roots for water and space, or when they receive too much shade depending on the canopy structure. Irises like full sun. But if they grow in full sun and in a hot summer climate that is dry, they will go dormant unless they have shade cover from other nearby plants.
Irises also need soil high in fertility and organic matter. Add sphagnum peat, compost leaves or rotted manure if necessary. If the soil has a clay texture, adding some sand may help. Prepare the beds a few weeks before planting the irises if they are to be planted in new beds. Add the organic material and a generous amount of commercial fertilizer (8-10 lbs. per 100 sq. feet of a complete fertilizer such as 8-8-8 or 8-24-24) and work in.
The best time to plant and divide Louisiana irises is mid-to-late August and September. Transplanting immediately after blooming is not recommended. If existing beds are to be divided and replanted, dig out all the irises and rework the beds, adding organic materials and a commercial fertilizer as described for new beds. Replant as soon as possible, preferably the same day. Do not allow the newly planted beds to dry out; water every few days until the plants are established. Planted in a triangular format (about 12 inches apart), they can be left 3 to 4 years and will form nice clumps. Irises grow in the direction they face; at least two offsets generally form each year, one on each side of the rhizome. Each rhizome blooms only once; then the offsets bloom the next year. Good growth and offset formation are, therefore, necessary each season for consistent bloom. The offsets represent vegetative reproduction and are identical in every respect to the parent rhizome.
Watering is necessary to have good blooms. The bloom season can last for 6-8 weeks since hybrid irises are either early, middle, or late season bloomers. Once new growth has begun, the beds should not be allowed to dry out. Know the dry periods of the year in your area. Give the iris beds a thorough soaking at least once weekly during those time periods. Modify the watering schedule according to growth.
For new or replanted beds (to which commercial fertilizer and organic material have been added at planting time), a light dressing of a complete fertilizer (2-4 lbs. per 100 square feet) is sufficient about two months prior to bloom (late January in Louisiana). Beds which have not been replanted in late summer are generally given two applications, a fairly heavy application at the start of the growing season (with good watering in), and then the light dressing just before bloom. Complete fertilizers such as 8-8-8 are preferable to high nitrogen fertilizers. High nitrogen can cause the plants to produce leafy growth while suppressing flowering; it can also make the plants more susceptible to disease.
Mulching is essential and serves many purposes, such as maintaining soil moisture and keeping weeds under control. But mulching during the summer dormant period serves one essential function which cannot be met by any other means, except planting the irises in water. The rhizomes lie on or very near the surface; the hot summer sun on the rhizomes (after the foliage has died back) will cause a condition known as sunscald. This causes the rhizome to deteriorate and rot. The tip of the rhizome will continue to grow, but it is almost a certainty that no blooms will be obtained the next season.
The problem is easily solved by applying mulch. About 2-3 inches of rotted or even semi-rotted leaves, bagasse (sugar cane fiber) or pine straw are excellent mulches. So is cotton burr compost. As little as one-half to one inch of soil can also be used if nothing else is available. But by all means, protect the rhizomes from the sun during the dormant period. Keeping mulch on the irises the entire year is best, and it is a necessity in in winter in colder areas. Use what is available in your backyard or commercially in your area.
What to do with spent bloom stalks: Unless you are a hybridizer or want to experiment by planting seeds, it is good practice to cut out spent bloom stalks. If you leave them, the seeds will drop, and rogue seedlings will appear among your irises. If you wish to maintain the identity of your plants, that can’t be allowed to happen. Therefore, cut out bloom stalks to within an inch or two from the ground as soon as the last flower blooms. That way, you remove the seed pods and the stalk on which they now hang. Also, the remaining energy in the rhizome will be able to create offsets or encourage the growth of those already present. Spent bloom stalks also become unattractive, and a clump of foliage will look better through the summer if they have been removed.
Garden clean-up: In the Fall, clear out the brown and yellowed foliage. Even with the best gardening practices, a few leaves in a fan turn yellow from time to time. It is best not to leave those to decompose in the garden, because they can harbor disease such as rust. Rust is one of the relatively few problems to confront irises. If you see a little in the spring, it is best to remove the foliage immediately and put it in the garbage can. You can also spray a fungicide. Generally rust is a problem at the end of the bloom season.
The growing range of Louisiana irises extends throughout much of the United States and even into Ontario, Canada. Some geographic areas are naturally inhospitable or more difficult to grow these irises in—the desert southwest, the Rocky Mountains and adjacent high plains, and specific regions of the northern United States. But this depends on the extent of winter and microclimates. Over time as natural and purposeful hybridization has occurred, Louisiana cultivars have developed a tolerance for weather beyond the norm of the Gulf Coast region, which people tend to associate them with.
Ideal growing conditions have a lot to do with the soil acidity and, if in a cold climate, protection during the winter. These irises do not like high alkalinity or excessive acidity, even if wet. The ideal pH range is 6.5 to 7.2, slight acidity to slight alkalinity. At times, people have thought that Louisiana irises needed acidic soil, because some species like I. fulva grow in river deltas or swamps. But this is not the case, which is good news for many gardeners because soil pH can be adjusted. As far as cold climates are concerned, Louisiana irises require mulch and/or snow cover. If the ground freezes and they are not protected, they will not survive into spring. Finally, for those growing in dry areas such as in the southwest, Louisiana irises can be grown in water gardens or under water culture, even if not in the native soil.
Louisiana irises need not be grown in water or under bog conditions, although they do well in both environments. However, there are additional options. They can grow directly in the soil, in containers, in large tubs, in raised beds, and in big barrels or irrigation tanks. Some gardeners experiment with large cement mixing tub containers (with a varied combination of soil and mulch materials) that do not drain. Also, since all irises vegetatively reproduce, consider the space constraints of the location you choose so that the irises have room to grow. For instance, a very small container that is just big enough for one rhizome will not provide room for the iris to reproduce.
Louisiana irises like sunlight. Plant them in areas where they get at least a half day of sun. Dappled sunlight provided by a very tall tree canopy can provide enough sunlight and needed shade in the summer. However, irises do not like to grow directly under trees where they must compete with the roots for water and space, or when they receive too much shade depending on the canopy structure. Irises like full sun. But if they grow in full sun and in a hot summer climate that is dry, they will go dormant unless they have shade cover from other nearby plants.
Irises also need soil high in fertility and organic matter. Add sphagnum peat, compost leaves or rotted manure if necessary. If the soil has a clay texture, adding some sand may help. Prepare the beds a few weeks before planting the irises if they are to be planted in new beds. Add the organic material and a generous amount of commercial fertilizer (8-10 lbs. per 100 sq. feet of a complete fertilizer such as 8-8-8 or 8-24-24) and work in.
The best time to plant and divide Louisiana irises is mid-to-late August and September. Transplanting immediately after blooming is not recommended. If existing beds are to be divided and replanted, dig out all the irises and rework the beds, adding organic materials and a commercial fertilizer as described for new beds. Replant as soon as possible, preferably the same day. Do not allow the newly planted beds to dry out; water every few days until the plants are established. Planted in a triangular format (about 12 inches apart), they can be left 3 to 4 years and will form nice clumps. Irises grow in the direction they face; at least two offsets generally form each year, one on each side of the rhizome. Each rhizome blooms only once; then the offsets bloom the next year. Good growth and offset formation are, therefore, necessary each season for consistent bloom. The offsets represent vegetative reproduction and are identical in every respect to the parent rhizome.
Watering is necessary to have good blooms. The bloom season can last for 6-8 weeks since hybrid irises are either early, middle, or late season bloomers. Once new growth has begun, the beds should not be allowed to dry out. Know the dry periods of the year in your area. Give the iris beds a thorough soaking at least once weekly during those time periods. Modify the watering schedule according to growth.
For new or replanted beds (to which commercial fertilizer and organic material have been added at planting time), a light dressing of a complete fertilizer (2-4 lbs. per 100 square feet) is sufficient about two months prior to bloom (late January in Louisiana). Beds which have not been replanted in late summer are generally given two applications, a fairly heavy application at the start of the growing season (with good watering in), and then the light dressing just before bloom. Complete fertilizers such as 8-8-8 are preferable to high nitrogen fertilizers. High nitrogen can cause the plants to produce leafy growth while suppressing flowering; it can also make the plants more susceptible to disease.
Mulching is essential and serves many purposes, such as maintaining soil moisture and keeping weeds under control. But mulching during the summer dormant period serves one essential function which cannot be met by any other means, except planting the irises in water. The rhizomes lie on or very near the surface; the hot summer sun on the rhizomes (after the foliage has died back) will cause a condition known as sunscald. This causes the rhizome to deteriorate and rot. The tip of the rhizome will continue to grow, but it is almost a certainty that no blooms will be obtained the next season.
The problem is easily solved by applying mulch. About 2-3 inches of rotted or even semi-rotted leaves, bagasse (sugar cane fiber) or pine straw are excellent mulches. So is cotton burr compost. As little as one-half to one inch of soil can also be used if nothing else is available. But by all means, protect the rhizomes from the sun during the dormant period. Keeping mulch on the irises the entire year is best, and it is a necessity in in winter in colder areas. Use what is available in your backyard or commercially in your area.
What to do with spent bloom stalks: Unless you are a hybridizer or want to experiment by planting seeds, it is good practice to cut out spent bloom stalks. If you leave them, the seeds will drop, and rogue seedlings will appear among your irises. If you wish to maintain the identity of your plants, that can’t be allowed to happen. Therefore, cut out bloom stalks to within an inch or two from the ground as soon as the last flower blooms. That way, you remove the seed pods and the stalk on which they now hang. Also, the remaining energy in the rhizome will be able to create offsets or encourage the growth of those already present. Spent bloom stalks also become unattractive, and a clump of foliage will look better through the summer if they have been removed.
Garden clean-up: In the Fall, clear out the brown and yellowed foliage. Even with the best gardening practices, a few leaves in a fan turn yellow from time to time. It is best not to leave those to decompose in the garden, because they can harbor disease such as rust. Rust is one of the relatively few problems to confront irises. If you see a little in the spring, it is best to remove the foliage immediately and put it in the garbage can. You can also spray a fungicide. Generally rust is a problem at the end of the bloom season.
Louisiana iris growers may never imagine that they want to propagate their plants. Keeping up a garden is plenty of work, but the irises get crowded after several years, and the beds or containers will benefit from dividing the irises and replenishing the soil. And, suddenly, you’re in the propagation business, at least at a modest level.
We are interested in your experiences. Join our Society to meet and learn from others who grow Louisiana irises in your area. Our magazine, the Fleur de Lis, regularly includes stories and advice that show the regional variation in iris cultivation practices.
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