Cultivation of Bearded Irises
Bearded Irises, like most garden perennials, will grow in any good garden soil. Choose a sunny, well-drained location. Bearded Irises do not like wet feet! At least 6 to 8 hours of full sun is needed for maximum bloom. At least 2 to 3 weeks before planting, prepare the bed by digging to a depth of 10-12 inches, adding soil conditioners, (organic compost, aged manure) and a low nitrogen fertilizer, and thoroughly water in the bed. A high Nitrogen fertilizer or young manure will lead to rot. The soil ph should be 6.1 to 7.2. The symbol ph expresses the relative acidity or alkalinity of the soil. The neutral point of the scale is 7.0. Soil testing below a ph of 7 is acid, soil testing above ph 7.0 is alkaline. If your soil tests too alkaline, add aluminum sulfate or agricultural sulfur; if the soil tests too acidic, add hydrated lime.
When you receive your rhizomes from the supplier or at the sale, they will look like the illustration for planting below (photo link PG-1). The rhizome should be planted on a ridge with space for the roots on each side. In sandy loam, just cover the rhizome (example PG-2); In heavier soil, the top of the rhizome should be just above the soil level (example PG-3). Be certain that the roots are well seated. Rhizomes should be planted at least 12 to 18 inches apart. Closer planting will require more frequent digging and re-planting. Usually bearded irises are re-planted every 3 to 4 years. If you have 3 or more rhizomes of the same variety, they can be planted in a triangular pattern to give an instant clump effect. Water well, for the first week or so, to establish a good new root system. After that time, the plant should have adjusted.
Fertilizer should be applied as a side dressing about 6 weeks before bloom time (a major growth time) and again in October. Commercial fertilizers supply nitrogen, phosphorus, and potash. 5-10-10, for example is 5% nitrogen, 10% phosphorus, and 10% potash. Irises need all of these nutrients. Organic compost and aged manures supply very little nutrition (usually about 0.8-0.3-0.6) but are excellent soil conditioners. Carefully work the fertilizer into the soil, remembering that irises have shallow feeder roots that should not be disturbed, Be certain that the fertilizers do not rest on the rhizome as this will lead to rot. Alfalfa pellets or meal, well rotted compost or manure can be worked in as a side dressing, in early fall. Always water well, after fertilizing or side dressing, as iris plants cannot use nutrients in solid form.
Bearded irises multiply by vegetative increase with new plants growing from the 'mother' rhizome. There will usually be 3 or more increases each year from each mother rhizome. About every 3 to 4 years, it is necessary to dig and replant the clumps. About 4 to 6 weeks after bloom season (late June to late July) dig the clumps and divide by cutting the new growth from the mother rhizome. Each increase will look like the original plant that you planted. Discard the old mother rhizome. Cut the foliage back into an inverted vee about 4 to 5 inches above the rhizome. These rhizomes are now ready for replanting. Be certain that you dig only one clump at a time so that you can keep the variety name correct. Many gardeners are disappointed to discover that they have purchased an incorrectly labeled variety at a sale or auction. Maintain an up-to-date garden plat for each of your iris plantings and check the garden labels against the plat.
A sunny, well-drained location, moderate feeding, and the removal of weeds and competing plant growth should provide you with a healthy growth of bearded irises that will delight you with the quality and quantity of bloom produced.
-- Main.RPries - 2010-08-03