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Growing Irises in EAST GERMANY

It is possible to grow Louisiana irises with fair success in East Germany. They represent a new group of irises in the area, have good colors and substance and large blooms. Knowledge is limited and performance is variable and many varieties are being tried in order to evaluate performance. Some increase and thrive while others do not perform well. This testing has been in progress only a few years and results are not final. Hopefully commercial production can begin soon.

This nursery is located near Augustenhof in the northern part of East Germany, about 10 kilometers (6 miles) east of Schwerin, the largest nearby town. The Baltic Sea is about 30 km. (20 miles) distant and causes the climate to be somewhat milder than more southern locations in East Germany. Mean winter temperature is near 0°C (32°F) and the winter minimum temperature can go as low as -20°C (-5°F). Summer maximum temperature can reach 35°C (95°F). The mean annual temperature is near 8°C (47°F).

The winter of 1985-1986 was very bad in terms of sustained cold and the Louisianas performed poorly. Temperatures reaching -23°C (-9°F) were sustained for two periods, each of about a week duration. The ground remained frozen for a long period. None of the irises died but all leaves and the tops of some rhizomes rotted. All of the plants started new growth in April and made many offsets. However, bloom was very poor and the irises behaved more like foliage plants than flowering plants. Irises hybridized in colder areas of the United States, particularly the hybrids of Morgan and Rowlan, are now being tested.

Annual rainfall is 62 cm. (about 25 inches), most of which occurs in June and July. Snowcover is limited, probably due to proximity to the Baltic. In January and February 12-15 days with snowcover in excess of 1 cm. (one half inch) are experienced. Only very rarely is heavy snow, 20 cm. (8 inches) experienced. This limited snow does not give the cold protection heavy snow provides in parts of the United States.

With normal winters the bloom period for Louisianas is late June through mid July. Stalks are normally as high as the leaves, 80-100 cm. (32-40 inches). Blooms are good and large and substance is unusually good. Unfortunately there are no standards for comparison of blooms with the southern United States.


The irises are grown in normal garden beds and are also being tested in water culture. The garden soil is sandy and only 20-30 cm. (8-12 inches) deep with the lower soil being poor and gravelly. Soil is slightly acidic and no special treatments are required. Soils for Louisiana irises are rich in organic material with cattle or pig manure being added every 2-3 years.


Water culture is experimental. One objective is to determine the effect of fairly deep water for winter protection. During the fall, 1983, irises were planted in standing water about 40 cm. (16 inches) deep. Leaves remained green for some time but died back in later winter after very low temperatures. The pool was drained to a water level of about 5 cm. (2 inches) in early April. New leaves were very chlorotic but turned normal green color in about three weeks without adding iron or sulfur. It is still undetermined if water culture offers advantages over growing irises in beds.


Louisiana irises can be planted either in spring (April-May) or in the fall (September). It is preferred to dig and replant in September. Fall planting should not be too late to allow the plants to become established before very cold weather. Planting is always in full sun. Many varieties grow vigorously and produce many off-shoots. They should be planted about 50 cm. (20 inches) apart to avoid growing into each other, and can be left in the same place for about three years. New plants can be set out in the spring, but old plants look very unhappy in the spring due to the effects of winter and it is preferred not to disturb them.


In addition to manures, commercial acid fertilizers such as 12-4-12 (for Rhododendrons) is applied to the irises every 2-3 weeks during the growing season.


Louisianas get the same watering schedule as the Siberians, I. versicolor and I. pseudacorus. Watering is done daily during dry periods. Mulching is not done in the summer because of the cool summer climate. During the growing period mulching shows little or no difference in plant growth. It is desirable to mulch for winter protection. Useful mulches are straw, leaves, needle leaves and spruce branches. The mulch is put on in late October and remains until the end of March.


Chlorosis of foliage in early spring is the only problem. This generally corrects itself as the weather warms up in two or three weeks and no treatment is given.


Testing is underway in growing Louisiana irises from seed. The first planting of seed (from the United States) was done indoors in February, 1984. Some of the seedlings were chlorotic and died. Others seem to be thriving in the garden. Most were still small in 1986, and had not yet bloomed, but some had off-shoots. Growing later blooming and more cold-resistant plants. There has been only limited hybridizing in the United States with the objective of developing more hardy varieties.