You should cut them back right after they finish blooming . Onlt cut back the stem that the flowers were on , unless you have any tattered
or dead leaves ...
In general, iris rhizomes can be planted or moved at any time the ground can be dug. Digging within a month to six weeks of bloom time is likely to adversely affect the bloom but the plant will do fine. The conventional time to dig, divide and plant rhizomes is from four weeks after bloom to four weeks before first killing frost. Commercial gardens like to start digging and shipping in July and August. California's commercial gardens usually start their replanting in September and in some cases have continued into January.
Prepare the bed or spot for the iris by loosening the soil to at least 8 inches (deeper is better). Use raised rows or beds if drainage is a problem. Compost and other soil ammendments can be incorporated at this time. Manure based compost may cause rhizome rot unless it is very well aged so I recommend non manure based composts. The soil loosening process is an ideal time to apply either balanced or phosphorus fertilizer as phosphorus tends to stay where it is applied. In an ideal situation, the bed preparation would take place a month before the bed was planted in order for the microorganisms to start their action and for the soil to settle. However, I have planted within 15 minutes of preparing the bed and everything turned out fine. Not that I am recommending the immediate planting.
planting directionsThe recommended planting technique is shown to the left. Another good technique is to make the soil into mud and press the rhizome into the mud. With any method, the bottom of the rhizome should be in good contact with the soil and the top of the rhizome just under the surface of the soil. In hot climates, it is important to have some cover over the rhizome to prevent damage by the hot sun. Plant 6" to 24" apart. Groups of three of the same cultivar can be planted in an 10" to 15" triangle for an instant clump. Rhizomes planted between 6" and 12" apart should be thinned or divided every year. Rhizomes 18" to 24" apart should be dug and divided after two to four years.
I have successfully used liquid formulations containing Surflan (the active ingredient in various preemergent herbicides) immediately after planting to minimize the growth of weeds. There have been reports by others of significant to fatal damage to irises when using preemergents. If you elect to use a preemergent, I strongly recommend carefully following the manufacturer's instructions and testing the system to be used on a limited area or number of rhizomes before using it on the entire iris planting.
Part of the minimal care is to clean the iris beds of dead leaves and other debris in the spring before bloom time and again in the fall before winter. The cleaning makes the bed look better and is a key part in minimizing pest and disease problems. Conventional wisdom says to destroy the material removed from the beds by burning or putting it in the trash to get rid of the pests, their eggs and disease organisms. For environmental reasons, these two techniques are being discouraged by the regulatory agencies. If the waste material has to be composted on site, it needs to be composting by a process that achieves internal temperatures of 140 degrees for all of the material being composed.
When the clumps are finished blooming, removing the bloom stalks is recommended. Apparently there is a controversy about the best way to remove the bloom stalks. The easiest way is to bend the stalk in such a way that it snaps off the rhizome. I have found that bending the stalk back and on a line down the length of the rhizome works best for me. Feel free to experiment a little, just do it gently at first. The other technique is to cut the stalks with a sharp knife just above the rhizome.
Irises will do very well with 1" of water per week. Preferably in one soaking that gets 10" to 20" deep. Overhead watering is not recommended even though that is exactly what rain is, for those parts of the county where it rains in the summer. Irises can survive, increase and bloom satisfactorily with less water than 1 inch per week but the foliage is not likely to be as attractive and bloom may not be as impressive. Do not mulch irises during the summer. The high moisture and warm temperatures at the rhizome level are ideal conditions for rot or insect entry. Sunlight to the rhizome is useful for good performance and disease prevention. Drying out does not hurt a rhizome unless taken to the extreme. Mulching during the winter to prevent freeze/thaw heaving may be necessary in those parts of the country where snow cover is inadequate.
|There are a lot of regional differences in the recommendations for fertilization. The absolute best way is to have the soil analyzed and use the results to tailor the fertilizer to your combination of soil and climate. Iris are heavy feeders and will need some supplemental nutrients after the first year in new ground. Compost incorporated into the soil prior to planting can supply some nutrients. Fertilizer will probably be needed for the rest. A balanced fertilizer (like 10-10-10) or lower nitrogen fertilizer (like 5-10-10) are the two most common recommendations. A universal recommendation is to avoid the high nitrogen lawn type fertilizer (like 23-3-3). Potassium (the final number of the N-P-K) is generally not necessary. For long term plantings, most soils will also require calcium. Lime for acid soils or gypsum for alkaline soils are the usual recommendations for supplying calcium. Timing of fertilizer application has historically been late winter/early spring and again in late summer/early fall. More California gardeners are now fertilizing after bloom, some instead of before bloom. Put the fertilizer around the outside of the clump and avoid getting granules on the rhizome as the granule may damage the surface and allow the entry of pests or rot. Foliar fertilizers are acceptable but some small scale experiments are recommended before doing the entire planting
Courtesy of my garden group " Playing in the Dirt "
· 1 decade ago